[0/9] RISC-V: Apply Zicboz to clear_page and memset

Message ID	20221027130247.31634-1-ajones@ventanamicro.com
Headers	show Return-Path: <kvm-riscv-bounces+incoming=patchwork.ozlabs.org@lists.infradead.org> From: Andrew Jones <ajones@ventanamicro.com> To: linux-riscv@lists.infradead.org, kvm-riscv@lists.infradead.org Cc: Paul Walmsley <paul.walmsley@sifive.com>, Palmer Dabbelt <palmer@dabbelt.com>, Albert Ou <aou@eecs.berkeley.edu>, Anup Patel <apatel@ventanamicro.com>, Heiko Stuebner <heiko@sntech.de>, Conor Dooley <conor.dooley@microchip.com>, Atish Patra <atishp@rivosinc.com>, Jisheng Zhang <jszhang@kernel.org> Subject: [PATCH 0/9] RISC-V: Apply Zicboz to clear_page and memset Date: Thu, 27 Oct 2022 15:02:38 +0200 Message-Id: <20221027130247.31634-1-ajones@ventanamicro.com> MIME-Version: 1.0 preview: When the Zicboz extension is available we can more rapidly zero naturally aligned Zicboz block sized chunks of memory. As pages are always page aligned and are larger than any Zicboz block size will b [...] Content analysis details: (-0.2 points, 5.0 required) pts rule name description ---- ---------------------- -------------------------------------------------- -0.0 RCVD_IN_DNSWL_NONE RBL: Sender listed at https://www.dnswl.org/, no trust [2a00:1450:4864:20:0:0:0:42e listed in] [list.dnswl.org] -0.0 SPF_PASS SPF: sender matches SPF record 0.0 SPF_HELO_NONE SPF: HELO does not publish an SPF Record -0.1 DKIM_VALID_AU Message has a valid DKIM or DK signature from author's domain -0.1 DKIM_VALID Message has at least one valid DKIM or DK signature 0.1 DKIM_SIGNED Message has a DKIM or DK signature, not necessarily valid -0.1 DKIM_VALID_EF Message has a valid DKIM or DK signature from envelope-from domain Precedence: list Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "kvm-riscv" <kvm-riscv-bounces@lists.infradead.org> Errors-To: kvm-riscv-bounces+incoming=patchwork.ozlabs.org@lists.infradead.org
Series	RISC-V: Apply Zicboz to clear_page and memset \| expand [0/9] RISC-V: Apply Zicboz to clear_page and memset [1/9] RISC-V: Factor out body of riscv_init_cbom_blocksize loop [2/9] RISC-V: Add Zicboz detection and block size parsing [3/9] RISC-V: insn-def: Define cbo.zero [4/9] RISC-V: Use Zicboz in clear_page when available [5/9] RISC-V: KVM: Provide UAPI for Zicboz block size [6/9] RISC-V: KVM: Expose Zicboz to the guest [7/9] RISC-V: lib: Improve memset assembler formatting [8/9] RISC-V: lib: Use named labels in memset [9/9] RISC-V: Use Zicboz in memset when available

Andrew Jones Oct. 27, 2022, 1:02 p.m. UTC

When the Zicboz extension is available we can more rapidly zero naturally
aligned Zicboz block sized chunks of memory. As pages are always page
aligned and are larger than any Zicboz block size will be, then
clear_page() appears to be a good candidate for the extension. While cycle
count and energy consumption should also be considered, we can be pretty
certain that implementing clear_page() with the Zicboz extension is a win
by comparing the new dynamic instruction count with its current count[1].
Doing so we see that the new count is less than half the old count (see
patch4's commit message for more details). Another candidate for the
extension is memset(), but, since memset() isn't just used for zeroing
memory and it accepts arbitrarily aligned addresses and arbitrary sizes,
it's not as obvious if adding support for Zicboz will be an overall win.
In order to make a determination, I've done some analysis and wrote my
conclusions in the bullets below.

* When compiling the kernel without CONFIG_RISCV_ISA_ZICBOZ, memset()
  doesn't change, so that's fine.

* The overhead added to memset() when the Zicboz extension isn't present,
  but CONFIG_RISCV_ISA_ZICBOZ is selected, is 3 jumps to known targets,
  which I believe is fine.

* The overhead added to a memset() invocation which is not zeroing memory
  is 7 instructions, where 3 are branches. This seems fine and,
  furthermore, memset() is almost always invoked to zero memory (99% [2]).

* When memset() is invoked to zero memory, the proposed Zicboz extended
  memset() always has a lower dynamic instruction count than the current
  memset() as long as the input address is Zicboz block aligned and the
  length is >= the block size.

* When memset() is invoked to zero memory, the proposed Zicboz extended
  memset() is always worse for unaligned or too small inputs than the
  current memset(), but it's only at most a few dozen instructions worse.
  I think this is probably fine, especially considering the large majority
  of zeroing invocations are 64 bytes or larger and are aligned to a
  power-of-2 boundary, 64-byte or larger (77% [2]).

[1] I ported the functions under test to userspace and linked them with
    a test program. Then, I ran them under gdb with a script[3] which
    counted instructions by single stepping.

[2] I wrote bpftrace scripts[4] to count memset() invocations to see the
    frequency of it being used to zero memory and have block size aligned
    input addresses with block size or larger lengths. The workload was
    just random desktop stuff including streaming video and compiling.
    While I did run this on my x86 notebook, I still expect the data to
    be representative on RISC-V. Note, x86 has clear_page() so the
    memset() data regarding alignment and size weren't over inflated by
    page zeroing invocations. Grepping also shows the large majority of
    memset() calls are to zero memory (93%).

[3] https://gist.github.com/jones-drew/487791c956ceca8c18adc2847eec9c60
[4] https://gist.github.com/jones-drew/1e860692cf6fc0fb2a82a04c9ce720fe

These patches are based on the following pending series

1. "[PATCH v2 0/3] RISC-V: Ensure Zicbom has a valid block size"
   20221024091309.406906-1-ajones@ventanamicro.com

2. "[PATCH 0/8] riscv: improve boot time isa extensions handling"
   20221006070818.3616-1-jszhang@kernel.org
   Also including the additional patch proposed here
   20221013162038.ehseju2neic2xu5z@kamzik

The patches are also available here
https://github.com/jones-drew/linux/commits/riscv/zicboz

To test over QEMU this branch may be used to enable Zicboz
https://gitlab.com/jones-drew/qemu/-/commits/riscv/zicboz

To test running a KVM guest with Zicboz this kvmtool branch may be used
https://github.com/jones-drew/kvmtool/commits/riscv/zicboz

Thanks,
drew

Andrew Jones (9):
  RISC-V: Factor out body of riscv_init_cbom_blocksize loop
  RISC-V: Add Zicboz detection and block size parsing
  RISC-V: insn-def: Define cbo.zero
  RISC-V: Use Zicboz in clear_page when available
  RISC-V: KVM: Provide UAPI for Zicboz block size
  RISC-V: KVM: Expose Zicboz to the guest
  RISC-V: lib: Improve memset assembler formatting
  RISC-V: lib: Use named labels in memset
  RISC-V: Use Zicboz in memset when available

 arch/riscv/Kconfig                  |  13 ++
 arch/riscv/include/asm/cacheflush.h |   3 +-
 arch/riscv/include/asm/hwcap.h      |   1 +
 arch/riscv/include/asm/insn-def.h   |  50 ++++++
 arch/riscv/include/asm/page.h       |   6 +-
 arch/riscv/include/uapi/asm/kvm.h   |   2 +
 arch/riscv/kernel/cpu.c             |   1 +
 arch/riscv/kernel/cpufeature.c      |  10 ++
 arch/riscv/kernel/setup.c           |   2 +-
 arch/riscv/kvm/vcpu.c               |  11 ++
 arch/riscv/lib/Makefile             |   1 +
 arch/riscv/lib/clear_page.S         |  28 ++++
 arch/riscv/lib/memset.S             | 241 +++++++++++++++++++---------
 arch/riscv/mm/cacheflush.c          |  64 +++++---
 14 files changed, 325 insertions(+), 108 deletions(-)
 create mode 100644 arch/riscv/lib/clear_page.S

Andrew Jones Oct. 29, 2022, 9:59 a.m. UTC | #1

On Thu, Oct 27, 2022 at 03:02:38PM +0200, Andrew Jones wrote:
> When the Zicboz extension is available we can more rapidly zero naturally
> aligned Zicboz block sized chunks of memory. As pages are always page
> aligned and are larger than any Zicboz block size will be, then
> clear_page() appears to be a good candidate for the extension. While cycle
> count and energy consumption should also be considered, we can be pretty
> certain that implementing clear_page() with the Zicboz extension is a win
> by comparing the new dynamic instruction count with its current count[1].
> Doing so we see that the new count is less than half the old count (see
> patch4's commit message for more details). Another candidate for the
> extension is memset(), but, since memset() isn't just used for zeroing
> memory and it accepts arbitrarily aligned addresses and arbitrary sizes,
> it's not as obvious if adding support for Zicboz will be an overall win.
> In order to make a determination, I've done some analysis and wrote my
> conclusions in the bullets below.
> 
> * When compiling the kernel without CONFIG_RISCV_ISA_ZICBOZ, memset()
>   doesn't change, so that's fine.
> 
> * The overhead added to memset() when the Zicboz extension isn't present,
>   but CONFIG_RISCV_ISA_ZICBOZ is selected, is 3 jumps to known targets,
>   which I believe is fine.
> 
> * The overhead added to a memset() invocation which is not zeroing memory
>   is 7 instructions, where 3 are branches. This seems fine and,
>   furthermore, memset() is almost always invoked to zero memory (99% [2]).
> 
> * When memset() is invoked to zero memory, the proposed Zicboz extended
>   memset() always has a lower dynamic instruction count than the current
>   memset() as long as the input address is Zicboz block aligned and the
>   length is >= the block size.
> 
> * When memset() is invoked to zero memory, the proposed Zicboz extended
>   memset() is always worse for unaligned or too small inputs than the
>   current memset(), but it's only at most a few dozen instructions worse.
>   I think this is probably fine, especially considering the large majority
>   of zeroing invocations are 64 bytes or larger and are aligned to a
>   power-of-2 boundary, 64-byte or larger (77% [2]).
> 
> [1] I ported the functions under test to userspace and linked them with
>     a test program. Then, I ran them under gdb with a script[3] which
>     counted instructions by single stepping.
> 
> [2] I wrote bpftrace scripts[4] to count memset() invocations to see the
>     frequency of it being used to zero memory and have block size aligned
>     input addresses with block size or larger lengths. The workload was
>     just random desktop stuff including streaming video and compiling.
>     While I did run this on my x86 notebook, I still expect the data to
>     be representative on RISC-V. Note, x86 has clear_page() so the
>     memset() data regarding alignment and size weren't over inflated by
>     page zeroing invocations. Grepping also shows the large majority of
>     memset() calls are to zero memory (93%).
> 
> [3] https://gist.github.com/jones-drew/487791c956ceca8c18adc2847eec9c60
> [4] https://gist.github.com/jones-drew/1e860692cf6fc0fb2a82a04c9ce720fe
> 
> These patches are based on the following pending series
> 
> 1. "[PATCH v2 0/3] RISC-V: Ensure Zicbom has a valid block size"
>    20221024091309.406906-1-ajones@ventanamicro.com
> 
> 2. "[PATCH 0/8] riscv: improve boot time isa extensions handling"
>    20221006070818.3616-1-jszhang@kernel.org
>    Also including the additional patch proposed here
>    20221013162038.ehseju2neic2xu5z@kamzik
> 
> The patches are also available here
> https://github.com/jones-drew/linux/commits/riscv/zicboz
> 
> To test over QEMU this branch may be used to enable Zicboz
> https://gitlab.com/jones-drew/qemu/-/commits/riscv/zicboz
> 
> To test running a KVM guest with Zicboz this kvmtool branch may be used
> https://github.com/jones-drew/kvmtool/commits/riscv/zicboz
> 
> Thanks,
> drew
> 
> Andrew Jones (9):
>   RISC-V: Factor out body of riscv_init_cbom_blocksize loop
>   RISC-V: Add Zicboz detection and block size parsing
>   RISC-V: insn-def: Define cbo.zero
>   RISC-V: Use Zicboz in clear_page when available
>   RISC-V: KVM: Provide UAPI for Zicboz block size
>   RISC-V: KVM: Expose Zicboz to the guest
>   RISC-V: lib: Improve memset assembler formatting
>   RISC-V: lib: Use named labels in memset
>   RISC-V: Use Zicboz in memset when available
> 
>  arch/riscv/Kconfig                  |  13 ++
>  arch/riscv/include/asm/cacheflush.h |   3 +-
>  arch/riscv/include/asm/hwcap.h      |   1 +
>  arch/riscv/include/asm/insn-def.h   |  50 ++++++
>  arch/riscv/include/asm/page.h       |   6 +-
>  arch/riscv/include/uapi/asm/kvm.h   |   2 +
>  arch/riscv/kernel/cpu.c             |   1 +
>  arch/riscv/kernel/cpufeature.c      |  10 ++
>  arch/riscv/kernel/setup.c           |   2 +-
>  arch/riscv/kvm/vcpu.c               |  11 ++
>  arch/riscv/lib/Makefile             |   1 +
>  arch/riscv/lib/clear_page.S         |  28 ++++
>  arch/riscv/lib/memset.S             | 241 +++++++++++++++++++---------
>  arch/riscv/mm/cacheflush.c          |  64 +++++---
>  14 files changed, 325 insertions(+), 108 deletions(-)
>  create mode 100644 arch/riscv/lib/clear_page.S
> 
> -- 
> 2.37.3
>

FYI, I just tried this with clang. It compiles but doesn't boot when
Zicboz is present (it does boot when Zicboz is disabled in QEMU). I'm
suspicious of the ALTERNATIVE() stuff, but I'll debug more on Monday.
Also, I see building with LLVM=1 doesn't work, but that appears to be
an issue introduced with "[PATCH 0/8] riscv: improve boot time isa
extensions handling" which this series is based on.

drew

Conor Dooley Oct. 30, 2022, 8:23 p.m. UTC | #2

On Sat, Oct 29, 2022 at 11:59:53AM +0200, Andrew Jones wrote:
> On Thu, Oct 27, 2022 at 03:02:38PM +0200, Andrew Jones wrote:
> > When the Zicboz extension is available we can more rapidly zero naturally
> > aligned Zicboz block sized chunks of memory. As pages are always page
> > aligned and are larger than any Zicboz block size will be, then
> > clear_page() appears to be a good candidate for the extension. While cycle
> > count and energy consumption should also be considered, we can be pretty
> > certain that implementing clear_page() with the Zicboz extension is a win
> > by comparing the new dynamic instruction count with its current count[1].
> > Doing so we see that the new count is less than half the old count (see
> > patch4's commit message for more details). Another candidate for the
> > extension is memset(), but, since memset() isn't just used for zeroing
> > memory and it accepts arbitrarily aligned addresses and arbitrary sizes,
> > it's not as obvious if adding support for Zicboz will be an overall win.
> > In order to make a determination, I've done some analysis and wrote my
> > conclusions in the bullets below.
> > 
> > * When compiling the kernel without CONFIG_RISCV_ISA_ZICBOZ, memset()
> >   doesn't change, so that's fine.
> > 
> > * The overhead added to memset() when the Zicboz extension isn't present,
> >   but CONFIG_RISCV_ISA_ZICBOZ is selected, is 3 jumps to known targets,
> >   which I believe is fine.
> > 
> > * The overhead added to a memset() invocation which is not zeroing memory
> >   is 7 instructions, where 3 are branches. This seems fine and,
> >   furthermore, memset() is almost always invoked to zero memory (99% [2]).
> > 
> > * When memset() is invoked to zero memory, the proposed Zicboz extended
> >   memset() always has a lower dynamic instruction count than the current
> >   memset() as long as the input address is Zicboz block aligned and the
> >   length is >= the block size.
> > 
> > * When memset() is invoked to zero memory, the proposed Zicboz extended
> >   memset() is always worse for unaligned or too small inputs than the
> >   current memset(), but it's only at most a few dozen instructions worse.
> >   I think this is probably fine, especially considering the large majority
> >   of zeroing invocations are 64 bytes or larger and are aligned to a
> >   power-of-2 boundary, 64-byte or larger (77% [2]).
> > 
> > [1] I ported the functions under test to userspace and linked them with
> >     a test program. Then, I ran them under gdb with a script[3] which
> >     counted instructions by single stepping.
> > 
> > [2] I wrote bpftrace scripts[4] to count memset() invocations to see the
> >     frequency of it being used to zero memory and have block size aligned
> >     input addresses with block size or larger lengths. The workload was
> >     just random desktop stuff including streaming video and compiling.
> >     While I did run this on my x86 notebook, I still expect the data to
> >     be representative on RISC-V. Note, x86 has clear_page() so the
> >     memset() data regarding alignment and size weren't over inflated by
> >     page zeroing invocations. Grepping also shows the large majority of
> >     memset() calls are to zero memory (93%).
> > 
> > [3] https://gist.github.com/jones-drew/487791c956ceca8c18adc2847eec9c60
> > [4] https://gist.github.com/jones-drew/1e860692cf6fc0fb2a82a04c9ce720fe
> > 
> > These patches are based on the following pending series
> > 
> > 1. "[PATCH v2 0/3] RISC-V: Ensure Zicbom has a valid block size"
> >    20221024091309.406906-1-ajones@ventanamicro.com
> > 
> > 2. "[PATCH 0/8] riscv: improve boot time isa extensions handling"
> >    20221006070818.3616-1-jszhang@kernel.org
> >    Also including the additional patch proposed here
> >    20221013162038.ehseju2neic2xu5z@kamzik
> > 
> > The patches are also available here
> > https://github.com/jones-drew/linux/commits/riscv/zicboz
> > 
> > To test over QEMU this branch may be used to enable Zicboz
> > https://gitlab.com/jones-drew/qemu/-/commits/riscv/zicboz
> > 
> > To test running a KVM guest with Zicboz this kvmtool branch may be used
> > https://github.com/jones-drew/kvmtool/commits/riscv/zicboz
> > 
> > Thanks,
> > drew
> > 
> > Andrew Jones (9):
> >   RISC-V: Factor out body of riscv_init_cbom_blocksize loop
> >   RISC-V: Add Zicboz detection and block size parsing
> >   RISC-V: insn-def: Define cbo.zero
> >   RISC-V: Use Zicboz in clear_page when available
> >   RISC-V: KVM: Provide UAPI for Zicboz block size
> >   RISC-V: KVM: Expose Zicboz to the guest
> >   RISC-V: lib: Improve memset assembler formatting
> >   RISC-V: lib: Use named labels in memset
> >   RISC-V: Use Zicboz in memset when available
> > 
> >  arch/riscv/Kconfig                  |  13 ++
> >  arch/riscv/include/asm/cacheflush.h |   3 +-
> >  arch/riscv/include/asm/hwcap.h      |   1 +
> >  arch/riscv/include/asm/insn-def.h   |  50 ++++++
> >  arch/riscv/include/asm/page.h       |   6 +-
> >  arch/riscv/include/uapi/asm/kvm.h   |   2 +
> >  arch/riscv/kernel/cpu.c             |   1 +
> >  arch/riscv/kernel/cpufeature.c      |  10 ++
> >  arch/riscv/kernel/setup.c           |   2 +-
> >  arch/riscv/kvm/vcpu.c               |  11 ++
> >  arch/riscv/lib/Makefile             |   1 +
> >  arch/riscv/lib/clear_page.S         |  28 ++++
> >  arch/riscv/lib/memset.S             | 241 +++++++++++++++++++---------
> >  arch/riscv/mm/cacheflush.c          |  64 +++++---
> >  14 files changed, 325 insertions(+), 108 deletions(-)
> >  create mode 100644 arch/riscv/lib/clear_page.S
> > 
> > -- 
> > 2.37.3
> >
> 
> FYI, I just tried this with clang. It compiles but doesn't boot when
> Zicboz is present (it does boot when Zicboz is disabled in QEMU). I'm
> suspicious of the ALTERNATIVE() stuff, but I'll debug more on Monday.
> Also, I see building with LLVM=1 doesn't work, but that appears to be
> an issue introduced with "[PATCH 0/8] riscv: improve boot time isa
> extensions handling" which this series is based on.

Yeah, I was hitting the LLVM failures when I gave it a go the other day,
thanks for passing it on to Jisheng.. I meant to do that and forgot.
FWIW, I did find a build error with gcc too:

riscv64-unknown-linux-gnu-ld: arch/riscv/purgatory/purgatory.ro: in function `.L3␂1':
ctype.c:(.text+0x215a): undefined reference to `riscv_cboz_block_size'

defconfig should be:
https://gist.github.com/ConchuOD/e14293a28b04dca2125bdcc0d97d366a
& toolchain stuff:
CONFIG_CC_VERSION_TEXT="riscv64-unknown-linux-gnu-gcc (g5964b5cd727) 11.1.0"
CONFIG_CC_IS_GCC=y
CONFIG_GCC_VERSION=110100
CONFIG_AS_IS_GNU=y
CONFIG_AS_VERSION=23700
CONFIG_LD_IS_BFD=y
CONFIG_LD_VERSION=23700

My toolchain predates zicbo* being introduced & I set the config option.
I didn't do any specific digging as to the cause.

Thanks,
Conor.

Andrew Jones Oct. 31, 2022, 8:39 a.m. UTC | #3

On Sun, Oct 30, 2022 at 08:23:27PM +0000, Conor Dooley wrote:
> On Sat, Oct 29, 2022 at 11:59:53AM +0200, Andrew Jones wrote:
> > On Thu, Oct 27, 2022 at 03:02:38PM +0200, Andrew Jones wrote:
> > > When the Zicboz extension is available we can more rapidly zero naturally
> > > aligned Zicboz block sized chunks of memory. As pages are always page
> > > aligned and are larger than any Zicboz block size will be, then
> > > clear_page() appears to be a good candidate for the extension. While cycle
> > > count and energy consumption should also be considered, we can be pretty
> > > certain that implementing clear_page() with the Zicboz extension is a win
> > > by comparing the new dynamic instruction count with its current count[1].
> > > Doing so we see that the new count is less than half the old count (see
> > > patch4's commit message for more details). Another candidate for the
> > > extension is memset(), but, since memset() isn't just used for zeroing
> > > memory and it accepts arbitrarily aligned addresses and arbitrary sizes,
> > > it's not as obvious if adding support for Zicboz will be an overall win.
> > > In order to make a determination, I've done some analysis and wrote my
> > > conclusions in the bullets below.
> > > 
> > > * When compiling the kernel without CONFIG_RISCV_ISA_ZICBOZ, memset()
> > >   doesn't change, so that's fine.
> > > 
> > > * The overhead added to memset() when the Zicboz extension isn't present,
> > >   but CONFIG_RISCV_ISA_ZICBOZ is selected, is 3 jumps to known targets,
> > >   which I believe is fine.
> > > 
> > > * The overhead added to a memset() invocation which is not zeroing memory
> > >   is 7 instructions, where 3 are branches. This seems fine and,
> > >   furthermore, memset() is almost always invoked to zero memory (99% [2]).
> > > 
> > > * When memset() is invoked to zero memory, the proposed Zicboz extended
> > >   memset() always has a lower dynamic instruction count than the current
> > >   memset() as long as the input address is Zicboz block aligned and the
> > >   length is >= the block size.
> > > 
> > > * When memset() is invoked to zero memory, the proposed Zicboz extended
> > >   memset() is always worse for unaligned or too small inputs than the
> > >   current memset(), but it's only at most a few dozen instructions worse.
> > >   I think this is probably fine, especially considering the large majority
> > >   of zeroing invocations are 64 bytes or larger and are aligned to a
> > >   power-of-2 boundary, 64-byte or larger (77% [2]).
> > > 
> > > [1] I ported the functions under test to userspace and linked them with
> > >     a test program. Then, I ran them under gdb with a script[3] which
> > >     counted instructions by single stepping.
> > > 
> > > [2] I wrote bpftrace scripts[4] to count memset() invocations to see the
> > >     frequency of it being used to zero memory and have block size aligned
> > >     input addresses with block size or larger lengths. The workload was
> > >     just random desktop stuff including streaming video and compiling.
> > >     While I did run this on my x86 notebook, I still expect the data to
> > >     be representative on RISC-V. Note, x86 has clear_page() so the
> > >     memset() data regarding alignment and size weren't over inflated by
> > >     page zeroing invocations. Grepping also shows the large majority of
> > >     memset() calls are to zero memory (93%).
> > > 
> > > [3] https://gist.github.com/jones-drew/487791c956ceca8c18adc2847eec9c60
> > > [4] https://gist.github.com/jones-drew/1e860692cf6fc0fb2a82a04c9ce720fe
> > > 
> > > These patches are based on the following pending series
> > > 
> > > 1. "[PATCH v2 0/3] RISC-V: Ensure Zicbom has a valid block size"
> > >    20221024091309.406906-1-ajones@ventanamicro.com
> > > 
> > > 2. "[PATCH 0/8] riscv: improve boot time isa extensions handling"
> > >    20221006070818.3616-1-jszhang@kernel.org
> > >    Also including the additional patch proposed here
> > >    20221013162038.ehseju2neic2xu5z@kamzik
> > > 
> > > The patches are also available here
> > > https://github.com/jones-drew/linux/commits/riscv/zicboz
> > > 
> > > To test over QEMU this branch may be used to enable Zicboz
> > > https://gitlab.com/jones-drew/qemu/-/commits/riscv/zicboz
> > > 
> > > To test running a KVM guest with Zicboz this kvmtool branch may be used
> > > https://github.com/jones-drew/kvmtool/commits/riscv/zicboz
> > > 
> > > Thanks,
> > > drew
> > > 
> > > Andrew Jones (9):
> > >   RISC-V: Factor out body of riscv_init_cbom_blocksize loop
> > >   RISC-V: Add Zicboz detection and block size parsing
> > >   RISC-V: insn-def: Define cbo.zero
> > >   RISC-V: Use Zicboz in clear_page when available
> > >   RISC-V: KVM: Provide UAPI for Zicboz block size
> > >   RISC-V: KVM: Expose Zicboz to the guest
> > >   RISC-V: lib: Improve memset assembler formatting
> > >   RISC-V: lib: Use named labels in memset
> > >   RISC-V: Use Zicboz in memset when available
> > > 
> > >  arch/riscv/Kconfig                  |  13 ++
> > >  arch/riscv/include/asm/cacheflush.h |   3 +-
> > >  arch/riscv/include/asm/hwcap.h      |   1 +
> > >  arch/riscv/include/asm/insn-def.h   |  50 ++++++
> > >  arch/riscv/include/asm/page.h       |   6 +-
> > >  arch/riscv/include/uapi/asm/kvm.h   |   2 +
> > >  arch/riscv/kernel/cpu.c             |   1 +
> > >  arch/riscv/kernel/cpufeature.c      |  10 ++
> > >  arch/riscv/kernel/setup.c           |   2 +-
> > >  arch/riscv/kvm/vcpu.c               |  11 ++
> > >  arch/riscv/lib/Makefile             |   1 +
> > >  arch/riscv/lib/clear_page.S         |  28 ++++
> > >  arch/riscv/lib/memset.S             | 241 +++++++++++++++++++---------
> > >  arch/riscv/mm/cacheflush.c          |  64 +++++---
> > >  14 files changed, 325 insertions(+), 108 deletions(-)
> > >  create mode 100644 arch/riscv/lib/clear_page.S
> > > 
> > > -- 
> > > 2.37.3
> > >
> > 
> > FYI, I just tried this with clang. It compiles but doesn't boot when
> > Zicboz is present (it does boot when Zicboz is disabled in QEMU). I'm
> > suspicious of the ALTERNATIVE() stuff, but I'll debug more on Monday.
> > Also, I see building with LLVM=1 doesn't work, but that appears to be
> > an issue introduced with "[PATCH 0/8] riscv: improve boot time isa
> > extensions handling" which this series is based on.
> 
> Yeah, I was hitting the LLVM failures when I gave it a go the other day,
> thanks for passing it on to Jisheng.. I meant to do that and forgot.
> FWIW, I did find a build error with gcc too:
> 
> riscv64-unknown-linux-gnu-ld: arch/riscv/purgatory/purgatory.ro: in function `.L3␂1':
> ctype.c:(.text+0x215a): undefined reference to `riscv_cboz_block_size'

Oh, I didn't see that with my toolchain
 - gcc 12.1.0 (g1ea978e3066a)
 - binutils 2.39

I'll see if I can reproduce it.

Thanks,
drew

> 
> defconfig should be:
> https://gist.github.com/ConchuOD/e14293a28b04dca2125bdcc0d97d366a
> & toolchain stuff:
> CONFIG_CC_VERSION_TEXT="riscv64-unknown-linux-gnu-gcc (g5964b5cd727) 11.1.0"
> CONFIG_CC_IS_GCC=y
> CONFIG_GCC_VERSION=110100
> CONFIG_AS_IS_GNU=y
> CONFIG_AS_VERSION=23700
> CONFIG_LD_IS_BFD=y
> CONFIG_LD_VERSION=23700
> 
> My toolchain predates zicbo* being introduced & I set the config option.
> I didn't do any specific digging as to the cause.
> 
> Thanks,
> Conor.
>

Andrew Jones Nov. 1, 2022, 10:37 a.m. UTC | #4

On Thu, Oct 27, 2022 at 03:02:38PM +0200, Andrew Jones wrote:
> When the Zicboz extension is available we can more rapidly zero naturally
> aligned Zicboz block sized chunks of memory. As pages are always page
> aligned and are larger than any Zicboz block size will be, then
> clear_page() appears to be a good candidate for the extension. While cycle
> count and energy consumption should also be considered, we can be pretty
> certain that implementing clear_page() with the Zicboz extension is a win
> by comparing the new dynamic instruction count with its current count[1].
> Doing so we see that the new count is less than half the old count (see
> patch4's commit message for more details). Another candidate for the
> extension is memset(), but, since memset() isn't just used for zeroing
> memory and it accepts arbitrarily aligned addresses and arbitrary sizes,
> it's not as obvious if adding support for Zicboz will be an overall win.
> In order to make a determination, I've done some analysis and wrote my
> conclusions in the bullets below.
> 
> * When compiling the kernel without CONFIG_RISCV_ISA_ZICBOZ, memset()
>   doesn't change, so that's fine.
> 
> * The overhead added to memset() when the Zicboz extension isn't present,
>   but CONFIG_RISCV_ISA_ZICBOZ is selected, is 3 jumps to known targets,
>   which I believe is fine.
> 
> * The overhead added to a memset() invocation which is not zeroing memory
>   is 7 instructions, where 3 are branches. This seems fine and,
>   furthermore, memset() is almost always invoked to zero memory (99% [2]).
> 
> * When memset() is invoked to zero memory, the proposed Zicboz extended
>   memset() always has a lower dynamic instruction count than the current
>   memset() as long as the input address is Zicboz block aligned and the
>   length is >= the block size.
> 
> * When memset() is invoked to zero memory, the proposed Zicboz extended
>   memset() is always worse for unaligned or too small inputs than the
>   current memset(), but it's only at most a few dozen instructions worse.
>   I think this is probably fine, especially considering the large majority
>   of zeroing invocations are 64 bytes or larger and are aligned to a
>   power-of-2 boundary, 64-byte or larger (77% [2]).

FYI, I spotted a bug in the bpf script used for this result, so I fixed it
and reran it. The new result is 67%, which is no longer a large majority,
but still a solid majority.

> 
> [1] I ported the functions under test to userspace and linked them with
>     a test program. Then, I ran them under gdb with a script[3] which
>     counted instructions by single stepping.
> 
> [2] I wrote bpftrace scripts[4] to count memset() invocations to see the
>     frequency of it being used to zero memory and have block size aligned
>     input addresses with block size or larger lengths. The workload was
>     just random desktop stuff including streaming video and compiling.
>     While I did run this on my x86 notebook, I still expect the data to
>     be representative on RISC-V. Note, x86 has clear_page() so the
>     memset() data regarding alignment and size weren't over inflated by
>     page zeroing invocations. Grepping also shows the large majority of
>     memset() calls are to zero memory (93%).
> 
> [3] https://gist.github.com/jones-drew/487791c956ceca8c18adc2847eec9c60
> [4] https://gist.github.com/jones-drew/1e860692cf6fc0fb2a82a04c9ce720fe
> 
> These patches are based on the following pending series
> 
> 1. "[PATCH v2 0/3] RISC-V: Ensure Zicbom has a valid block size"
>    20221024091309.406906-1-ajones@ventanamicro.com
> 
> 2. "[PATCH 0/8] riscv: improve boot time isa extensions handling"
>    20221006070818.3616-1-jszhang@kernel.org
>    Also including the additional patch proposed here
>    20221013162038.ehseju2neic2xu5z@kamzik
> 
> The patches are also available here
> https://github.com/jones-drew/linux/commits/riscv/zicboz
> 
> To test over QEMU this branch may be used to enable Zicboz
> https://gitlab.com/jones-drew/qemu/-/commits/riscv/zicboz
> 
> To test running a KVM guest with Zicboz this kvmtool branch may be used
> https://github.com/jones-drew/kvmtool/commits/riscv/zicboz
> 
> Thanks,
> drew
> 
> Andrew Jones (9):
>   RISC-V: Factor out body of riscv_init_cbom_blocksize loop
>   RISC-V: Add Zicboz detection and block size parsing
>   RISC-V: insn-def: Define cbo.zero
>   RISC-V: Use Zicboz in clear_page when available
>   RISC-V: KVM: Provide UAPI for Zicboz block size
>   RISC-V: KVM: Expose Zicboz to the guest
>   RISC-V: lib: Improve memset assembler formatting
>   RISC-V: lib: Use named labels in memset
>   RISC-V: Use Zicboz in memset when available
> 
>  arch/riscv/Kconfig                  |  13 ++
>  arch/riscv/include/asm/cacheflush.h |   3 +-
>  arch/riscv/include/asm/hwcap.h      |   1 +
>  arch/riscv/include/asm/insn-def.h   |  50 ++++++
>  arch/riscv/include/asm/page.h       |   6 +-
>  arch/riscv/include/uapi/asm/kvm.h   |   2 +
>  arch/riscv/kernel/cpu.c             |   1 +
>  arch/riscv/kernel/cpufeature.c      |  10 ++
>  arch/riscv/kernel/setup.c           |   2 +-
>  arch/riscv/kvm/vcpu.c               |  11 ++
>  arch/riscv/lib/Makefile             |   1 +
>  arch/riscv/lib/clear_page.S         |  28 ++++
>  arch/riscv/lib/memset.S             | 241 +++++++++++++++++++---------
>  arch/riscv/mm/cacheflush.c          |  64 +++++---
>  14 files changed, 325 insertions(+), 108 deletions(-)
>  create mode 100644 arch/riscv/lib/clear_page.S
> 
> -- 
> 2.37.3
>

Andrew Jones Nov. 1, 2022, 10:53 a.m. UTC | #5

On Tue, Nov 01, 2022 at 11:37:11AM +0100, Andrew Jones wrote:
> On Thu, Oct 27, 2022 at 03:02:38PM +0200, Andrew Jones wrote:
> > When the Zicboz extension is available we can more rapidly zero naturally
> > aligned Zicboz block sized chunks of memory. As pages are always page
> > aligned and are larger than any Zicboz block size will be, then
> > clear_page() appears to be a good candidate for the extension. While cycle
> > count and energy consumption should also be considered, we can be pretty
> > certain that implementing clear_page() with the Zicboz extension is a win
> > by comparing the new dynamic instruction count with its current count[1].
> > Doing so we see that the new count is less than half the old count (see
> > patch4's commit message for more details). Another candidate for the
> > extension is memset(), but, since memset() isn't just used for zeroing
> > memory and it accepts arbitrarily aligned addresses and arbitrary sizes,
> > it's not as obvious if adding support for Zicboz will be an overall win.
> > In order to make a determination, I've done some analysis and wrote my
> > conclusions in the bullets below.
> > 
> > * When compiling the kernel without CONFIG_RISCV_ISA_ZICBOZ, memset()
> >   doesn't change, so that's fine.
> > 
> > * The overhead added to memset() when the Zicboz extension isn't present,
> >   but CONFIG_RISCV_ISA_ZICBOZ is selected, is 3 jumps to known targets,
> >   which I believe is fine.
> > 
> > * The overhead added to a memset() invocation which is not zeroing memory
> >   is 7 instructions, where 3 are branches. This seems fine and,
> >   furthermore, memset() is almost always invoked to zero memory (99% [2]).
> > 
> > * When memset() is invoked to zero memory, the proposed Zicboz extended
> >   memset() always has a lower dynamic instruction count than the current
> >   memset() as long as the input address is Zicboz block aligned and the
> >   length is >= the block size.
> > 
> > * When memset() is invoked to zero memory, the proposed Zicboz extended
> >   memset() is always worse for unaligned or too small inputs than the
> >   current memset(), but it's only at most a few dozen instructions worse.
> >   I think this is probably fine, especially considering the large majority
> >   of zeroing invocations are 64 bytes or larger and are aligned to a
> >   power-of-2 boundary, 64-byte or larger (77% [2]).
> 
> FYI, I spotted a bug in the bpf script used for this result, so I fixed it
> and reran it. The new result is 67%, which is no longer a large majority,
> but still a solid majority.

Additionally, I've now seen on a mostly idle system that at least half the
objects getting zeroed were too small (< 64 bytes). Considering the memset
profile is workload dependent, it's difficult to say with certainty that
we should patch it. More experiments are likely necessary.

> 
> > 
> > [1] I ported the functions under test to userspace and linked them with
> >     a test program. Then, I ran them under gdb with a script[3] which
> >     counted instructions by single stepping.
> > 
> > [2] I wrote bpftrace scripts[4] to count memset() invocations to see the
> >     frequency of it being used to zero memory and have block size aligned
> >     input addresses with block size or larger lengths. The workload was
> >     just random desktop stuff including streaming video and compiling.
> >     While I did run this on my x86 notebook, I still expect the data to
> >     be representative on RISC-V. Note, x86 has clear_page() so the
> >     memset() data regarding alignment and size weren't over inflated by
> >     page zeroing invocations. Grepping also shows the large majority of
> >     memset() calls are to zero memory (93%).
> > 
> > [3] https://gist.github.com/jones-drew/487791c956ceca8c18adc2847eec9c60
> > [4] https://gist.github.com/jones-drew/1e860692cf6fc0fb2a82a04c9ce720fe
> > 
> > These patches are based on the following pending series
> > 
> > 1. "[PATCH v2 0/3] RISC-V: Ensure Zicbom has a valid block size"
> >    20221024091309.406906-1-ajones@ventanamicro.com
> > 
> > 2. "[PATCH 0/8] riscv: improve boot time isa extensions handling"
> >    20221006070818.3616-1-jszhang@kernel.org
> >    Also including the additional patch proposed here
> >    20221013162038.ehseju2neic2xu5z@kamzik
> > 
> > The patches are also available here
> > https://github.com/jones-drew/linux/commits/riscv/zicboz
> > 
> > To test over QEMU this branch may be used to enable Zicboz
> > https://gitlab.com/jones-drew/qemu/-/commits/riscv/zicboz
> > 
> > To test running a KVM guest with Zicboz this kvmtool branch may be used
> > https://github.com/jones-drew/kvmtool/commits/riscv/zicboz
> > 
> > Thanks,
> > drew
> > 
> > Andrew Jones (9):
> >   RISC-V: Factor out body of riscv_init_cbom_blocksize loop
> >   RISC-V: Add Zicboz detection and block size parsing
> >   RISC-V: insn-def: Define cbo.zero
> >   RISC-V: Use Zicboz in clear_page when available
> >   RISC-V: KVM: Provide UAPI for Zicboz block size
> >   RISC-V: KVM: Expose Zicboz to the guest
> >   RISC-V: lib: Improve memset assembler formatting
> >   RISC-V: lib: Use named labels in memset
> >   RISC-V: Use Zicboz in memset when available
> > 
> >  arch/riscv/Kconfig                  |  13 ++
> >  arch/riscv/include/asm/cacheflush.h |   3 +-
> >  arch/riscv/include/asm/hwcap.h      |   1 +
> >  arch/riscv/include/asm/insn-def.h   |  50 ++++++
> >  arch/riscv/include/asm/page.h       |   6 +-
> >  arch/riscv/include/uapi/asm/kvm.h   |   2 +
> >  arch/riscv/kernel/cpu.c             |   1 +
> >  arch/riscv/kernel/cpufeature.c      |  10 ++
> >  arch/riscv/kernel/setup.c           |   2 +-
> >  arch/riscv/kvm/vcpu.c               |  11 ++
> >  arch/riscv/lib/Makefile             |   1 +
> >  arch/riscv/lib/clear_page.S         |  28 ++++
> >  arch/riscv/lib/memset.S             | 241 +++++++++++++++++++---------
> >  arch/riscv/mm/cacheflush.c          |  64 +++++---
> >  14 files changed, 325 insertions(+), 108 deletions(-)
> >  create mode 100644 arch/riscv/lib/clear_page.S
> > 
> > -- 
> > 2.37.3
> >

Conor Dooley Dec. 20, 2022, 12:55 p.m. UTC | #6

Hey Drew,

I assume you're not gonna respin this one before the xmas holidays etc,
but a v2 is on the cards, right?

Thanks,
Conor.

On Thu, Oct 27, 2022 at 03:02:38PM +0200, Andrew Jones wrote:
> When the Zicboz extension is available we can more rapidly zero naturally
> aligned Zicboz block sized chunks of memory. As pages are always page
> aligned and are larger than any Zicboz block size will be, then
> clear_page() appears to be a good candidate for the extension. While cycle
> count and energy consumption should also be considered, we can be pretty
> certain that implementing clear_page() with the Zicboz extension is a win
> by comparing the new dynamic instruction count with its current count[1].
> Doing so we see that the new count is less than half the old count (see
> patch4's commit message for more details). Another candidate for the
> extension is memset(), but, since memset() isn't just used for zeroing
> memory and it accepts arbitrarily aligned addresses and arbitrary sizes,
> it's not as obvious if adding support for Zicboz will be an overall win.
> In order to make a determination, I've done some analysis and wrote my
> conclusions in the bullets below.
> 
> * When compiling the kernel without CONFIG_RISCV_ISA_ZICBOZ, memset()
>   doesn't change, so that's fine.
> 
> * The overhead added to memset() when the Zicboz extension isn't present,
>   but CONFIG_RISCV_ISA_ZICBOZ is selected, is 3 jumps to known targets,
>   which I believe is fine.
> 
> * The overhead added to a memset() invocation which is not zeroing memory
>   is 7 instructions, where 3 are branches. This seems fine and,
>   furthermore, memset() is almost always invoked to zero memory (99% [2]).
> 
> * When memset() is invoked to zero memory, the proposed Zicboz extended
>   memset() always has a lower dynamic instruction count than the current
>   memset() as long as the input address is Zicboz block aligned and the
>   length is >= the block size.
> 
> * When memset() is invoked to zero memory, the proposed Zicboz extended
>   memset() is always worse for unaligned or too small inputs than the
>   current memset(), but it's only at most a few dozen instructions worse.
>   I think this is probably fine, especially considering the large majority
>   of zeroing invocations are 64 bytes or larger and are aligned to a
>   power-of-2 boundary, 64-byte or larger (77% [2]).
> 
> [1] I ported the functions under test to userspace and linked them with
>     a test program. Then, I ran them under gdb with a script[3] which
>     counted instructions by single stepping.
> 
> [2] I wrote bpftrace scripts[4] to count memset() invocations to see the
>     frequency of it being used to zero memory and have block size aligned
>     input addresses with block size or larger lengths. The workload was
>     just random desktop stuff including streaming video and compiling.
>     While I did run this on my x86 notebook, I still expect the data to
>     be representative on RISC-V. Note, x86 has clear_page() so the
>     memset() data regarding alignment and size weren't over inflated by
>     page zeroing invocations. Grepping also shows the large majority of
>     memset() calls are to zero memory (93%).
> 
> [3] https://gist.github.com/jones-drew/487791c956ceca8c18adc2847eec9c60
> [4] https://gist.github.com/jones-drew/1e860692cf6fc0fb2a82a04c9ce720fe
> 
> These patches are based on the following pending series
> 
> 1. "[PATCH v2 0/3] RISC-V: Ensure Zicbom has a valid block size"
>    20221024091309.406906-1-ajones@ventanamicro.com
> 
> 2. "[PATCH 0/8] riscv: improve boot time isa extensions handling"
>    20221006070818.3616-1-jszhang@kernel.org
>    Also including the additional patch proposed here
>    20221013162038.ehseju2neic2xu5z@kamzik
> 
> The patches are also available here
> https://github.com/jones-drew/linux/commits/riscv/zicboz
> 
> To test over QEMU this branch may be used to enable Zicboz
> https://gitlab.com/jones-drew/qemu/-/commits/riscv/zicboz
> 
> To test running a KVM guest with Zicboz this kvmtool branch may be used
> https://github.com/jones-drew/kvmtool/commits/riscv/zicboz
> 
> Thanks,
> drew
> 
> Andrew Jones (9):
>   RISC-V: Factor out body of riscv_init_cbom_blocksize loop
>   RISC-V: Add Zicboz detection and block size parsing
>   RISC-V: insn-def: Define cbo.zero
>   RISC-V: Use Zicboz in clear_page when available
>   RISC-V: KVM: Provide UAPI for Zicboz block size
>   RISC-V: KVM: Expose Zicboz to the guest
>   RISC-V: lib: Improve memset assembler formatting
>   RISC-V: lib: Use named labels in memset
>   RISC-V: Use Zicboz in memset when available
> 
>  arch/riscv/Kconfig                  |  13 ++
>  arch/riscv/include/asm/cacheflush.h |   3 +-
>  arch/riscv/include/asm/hwcap.h      |   1 +
>  arch/riscv/include/asm/insn-def.h   |  50 ++++++
>  arch/riscv/include/asm/page.h       |   6 +-
>  arch/riscv/include/uapi/asm/kvm.h   |   2 +
>  arch/riscv/kernel/cpu.c             |   1 +
>  arch/riscv/kernel/cpufeature.c      |  10 ++
>  arch/riscv/kernel/setup.c           |   2 +-
>  arch/riscv/kvm/vcpu.c               |  11 ++
>  arch/riscv/lib/Makefile             |   1 +
>  arch/riscv/lib/clear_page.S         |  28 ++++
>  arch/riscv/lib/memset.S             | 241 +++++++++++++++++++---------
>  arch/riscv/mm/cacheflush.c          |  64 +++++---
>  14 files changed, 325 insertions(+), 108 deletions(-)
>  create mode 100644 arch/riscv/lib/clear_page.S
> 
> -- 
> 2.37.3
> 
> 
> _______________________________________________
> linux-riscv mailing list
> linux-riscv@lists.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-riscv
>

Andrew Jones Dec. 26, 2022, 6:56 p.m. UTC | #7

On Tue, Dec 20, 2022 at 12:55:07PM +0000, Conor Dooley wrote:
> Hey Drew,
> 
> I assume you're not gonna respin this one before the xmas holidays etc,
> but a v2 is on the cards, right?

Hi Conor,

A v2 is definitely on my TODO. I'll try to get one out soon.

Thanks,
drew

> 
> Thanks,
> Conor.
> 
> On Thu, Oct 27, 2022 at 03:02:38PM +0200, Andrew Jones wrote:
> > When the Zicboz extension is available we can more rapidly zero naturally
> > aligned Zicboz block sized chunks of memory. As pages are always page
> > aligned and are larger than any Zicboz block size will be, then
> > clear_page() appears to be a good candidate for the extension. While cycle
> > count and energy consumption should also be considered, we can be pretty
> > certain that implementing clear_page() with the Zicboz extension is a win
> > by comparing the new dynamic instruction count with its current count[1].
> > Doing so we see that the new count is less than half the old count (see
> > patch4's commit message for more details). Another candidate for the
> > extension is memset(), but, since memset() isn't just used for zeroing
> > memory and it accepts arbitrarily aligned addresses and arbitrary sizes,
> > it's not as obvious if adding support for Zicboz will be an overall win.
> > In order to make a determination, I've done some analysis and wrote my
> > conclusions in the bullets below.
> > 
> > * When compiling the kernel without CONFIG_RISCV_ISA_ZICBOZ, memset()
> >   doesn't change, so that's fine.
> > 
> > * The overhead added to memset() when the Zicboz extension isn't present,
> >   but CONFIG_RISCV_ISA_ZICBOZ is selected, is 3 jumps to known targets,
> >   which I believe is fine.
> > 
> > * The overhead added to a memset() invocation which is not zeroing memory
> >   is 7 instructions, where 3 are branches. This seems fine and,
> >   furthermore, memset() is almost always invoked to zero memory (99% [2]).
> > 
> > * When memset() is invoked to zero memory, the proposed Zicboz extended
> >   memset() always has a lower dynamic instruction count than the current
> >   memset() as long as the input address is Zicboz block aligned and the
> >   length is >= the block size.
> > 
> > * When memset() is invoked to zero memory, the proposed Zicboz extended
> >   memset() is always worse for unaligned or too small inputs than the
> >   current memset(), but it's only at most a few dozen instructions worse.
> >   I think this is probably fine, especially considering the large majority
> >   of zeroing invocations are 64 bytes or larger and are aligned to a
> >   power-of-2 boundary, 64-byte or larger (77% [2]).
> > 
> > [1] I ported the functions under test to userspace and linked them with
> >     a test program. Then, I ran them under gdb with a script[3] which
> >     counted instructions by single stepping.
> > 
> > [2] I wrote bpftrace scripts[4] to count memset() invocations to see the
> >     frequency of it being used to zero memory and have block size aligned
> >     input addresses with block size or larger lengths. The workload was
> >     just random desktop stuff including streaming video and compiling.
> >     While I did run this on my x86 notebook, I still expect the data to
> >     be representative on RISC-V. Note, x86 has clear_page() so the
> >     memset() data regarding alignment and size weren't over inflated by
> >     page zeroing invocations. Grepping also shows the large majority of
> >     memset() calls are to zero memory (93%).
> > 
> > [3] https://gist.github.com/jones-drew/487791c956ceca8c18adc2847eec9c60
> > [4] https://gist.github.com/jones-drew/1e860692cf6fc0fb2a82a04c9ce720fe
> > 
> > These patches are based on the following pending series
> > 
> > 1. "[PATCH v2 0/3] RISC-V: Ensure Zicbom has a valid block size"
> >    20221024091309.406906-1-ajones@ventanamicro.com
> > 
> > 2. "[PATCH 0/8] riscv: improve boot time isa extensions handling"
> >    20221006070818.3616-1-jszhang@kernel.org
> >    Also including the additional patch proposed here
> >    20221013162038.ehseju2neic2xu5z@kamzik
> > 
> > The patches are also available here
> > https://github.com/jones-drew/linux/commits/riscv/zicboz
> > 
> > To test over QEMU this branch may be used to enable Zicboz
> > https://gitlab.com/jones-drew/qemu/-/commits/riscv/zicboz
> > 
> > To test running a KVM guest with Zicboz this kvmtool branch may be used
> > https://github.com/jones-drew/kvmtool/commits/riscv/zicboz
> > 
> > Thanks,
> > drew
> > 
> > Andrew Jones (9):
> >   RISC-V: Factor out body of riscv_init_cbom_blocksize loop
> >   RISC-V: Add Zicboz detection and block size parsing
> >   RISC-V: insn-def: Define cbo.zero
> >   RISC-V: Use Zicboz in clear_page when available
> >   RISC-V: KVM: Provide UAPI for Zicboz block size
> >   RISC-V: KVM: Expose Zicboz to the guest
> >   RISC-V: lib: Improve memset assembler formatting
> >   RISC-V: lib: Use named labels in memset
> >   RISC-V: Use Zicboz in memset when available
> > 
> >  arch/riscv/Kconfig                  |  13 ++
> >  arch/riscv/include/asm/cacheflush.h |   3 +-
> >  arch/riscv/include/asm/hwcap.h      |   1 +
> >  arch/riscv/include/asm/insn-def.h   |  50 ++++++
> >  arch/riscv/include/asm/page.h       |   6 +-
> >  arch/riscv/include/uapi/asm/kvm.h   |   2 +
> >  arch/riscv/kernel/cpu.c             |   1 +
> >  arch/riscv/kernel/cpufeature.c      |  10 ++
> >  arch/riscv/kernel/setup.c           |   2 +-
> >  arch/riscv/kvm/vcpu.c               |  11 ++
> >  arch/riscv/lib/Makefile             |   1 +
> >  arch/riscv/lib/clear_page.S         |  28 ++++
> >  arch/riscv/lib/memset.S             | 241 +++++++++++++++++++---------
> >  arch/riscv/mm/cacheflush.c          |  64 +++++---
> >  14 files changed, 325 insertions(+), 108 deletions(-)
> >  create mode 100644 arch/riscv/lib/clear_page.S
> > 
> > -- 
> > 2.37.3
> > 
> > 
> > _______________________________________________
> > linux-riscv mailing list
> > linux-riscv@lists.infradead.org
> > http://lists.infradead.org/mailman/listinfo/linux-riscv
> >

[0/9] RISC-V: Apply Zicboz to clear_page and memset

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