Patchwork powerpc: Fix "attempt to move .org backwards" error

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Submitter Paul Mackerras
Date April 26, 2013, 3:51 a.m.
Message ID <20130426035140.GA5796@drongo>
Download mbox | patch
Permalink /patch/239649/
State Accepted
Commit a485c70989fc6e1b002ea8c323bc3fc2f1eab722
Delegated to: Benjamin Herrenschmidt
Headers show

Comments

Paul Mackerras - April 26, 2013, 3:51 a.m.
Building a 64-bit powerpc kernel with PR KVM enabled currently gives
this error:

  AS      arch/powerpc/kernel/head_64.o
arch/powerpc/kernel/exceptions-64s.S: Assembler messages:
arch/powerpc/kernel/exceptions-64s.S:258: Error: attempt to move .org backwards
make[2]: *** [arch/powerpc/kernel/head_64.o] Error 1

This happens because the MASKABLE_EXCEPTION_PSERIES macro turns into
33 instructions, but we only have space for 32 at the decrementer
interrupt vector (from 0x900 to 0x980).

In the code generated by the MASKABLE_EXCEPTION_PSERIES macro, we
currently have two instances of the HMT_MEDIUM macro, which has the
effect of setting the SMT thread priority to medium.  One is the
first instruction, and is overwritten by a no-op on processors where
we save the PPR (processor priority register), that is, POWER7 or
later.  The other is after we have saved the PPR.

In order to reduce the code at 0x900 by one instruction, we omit the
first HMT_MEDIUM.  On processors without SMT this will have no effect
since HMT_MEDIUM is a no-op there.  On POWER5 and RS64 machines this
will mean that the first few instructions take a little longer in the
case where a decrementer interrupt occurs when the hardware thread is
running at low SMT priority.  On POWER6 and later machines, the
hardware automatically boosts the thread priority when a decrementer
interrupt is taken if the thread priority was below medium, so this
change won't make any difference.

The alternative would be to branch out of line after saving the CFAR.
However, that would incur an extra overhead on all processors, whereas
the approach adopted here only adds overhead on older threaded processors.

Signed-off-by: Paul Mackerras <paulus@samba.org>
---
 arch/powerpc/include/asm/exception-64s.h |    2 +-
 arch/powerpc/kernel/exceptions-64s.S     |    7 ++++++-
 2 files changed, 7 insertions(+), 2 deletions(-)
Chen Gang - April 26, 2013, 4:13 a.m.
On 2013年04月26日 11:51, Paul Mackerras wrote:
> Building a 64-bit powerpc kernel with PR KVM enabled currently gives
> this error:
> 
>   AS      arch/powerpc/kernel/head_64.o
> arch/powerpc/kernel/exceptions-64s.S: Assembler messages:
> arch/powerpc/kernel/exceptions-64s.S:258: Error: attempt to move .org backwards
> make[2]: *** [arch/powerpc/kernel/head_64.o] Error 1
> 
> This happens because the MASKABLE_EXCEPTION_PSERIES macro turns into
> 33 instructions, but we only have space for 32 at the decrementer
> interrupt vector (from 0x900 to 0x980).
> 
> In the code generated by the MASKABLE_EXCEPTION_PSERIES macro, we
> currently have two instances of the HMT_MEDIUM macro, which has the
> effect of setting the SMT thread priority to medium.  One is the
> first instruction, and is overwritten by a no-op on processors where
> we save the PPR (processor priority register), that is, POWER7 or
> later.  The other is after we have saved the PPR.
> 
> In order to reduce the code at 0x900 by one instruction, we omit the
> first HMT_MEDIUM.  On processors without SMT this will have no effect
> since HMT_MEDIUM is a no-op there.  On POWER5 and RS64 machines this
> will mean that the first few instructions take a little longer in the
> case where a decrementer interrupt occurs when the hardware thread is
> running at low SMT priority.  On POWER6 and later machines, the
> hardware automatically boosts the thread priority when a decrementer
> interrupt is taken if the thread priority was below medium, so this
> change won't make any difference.
> 
> The alternative would be to branch out of line after saving the CFAR.
> However, that would incur an extra overhead on all processors, whereas
> the approach adopted here only adds overhead on older threaded processors.
> 
> Signed-off-by: Paul Mackerras <paulus@samba.org>
> ---

Hello Mike:

Please try Paul's patch, firstly.

:-)

Thanks.


>  arch/powerpc/include/asm/exception-64s.h |    2 +-
>  arch/powerpc/kernel/exceptions-64s.S     |    7 ++++++-
>  2 files changed, 7 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/powerpc/include/asm/exception-64s.h b/arch/powerpc/include/asm/exception-64s.h
> index 05e6d2e..8e5fae8 100644
> --- a/arch/powerpc/include/asm/exception-64s.h
> +++ b/arch/powerpc/include/asm/exception-64s.h
> @@ -414,7 +414,6 @@ label##_relon_hv:						\
>  #define SOFTEN_NOTEST_HV(vec)		_SOFTEN_TEST(EXC_HV, vec)
>  
>  #define __MASKABLE_EXCEPTION_PSERIES(vec, label, h, extra)		\
> -	HMT_MEDIUM_PPR_DISCARD;						\
>  	SET_SCRATCH0(r13);    /* save r13 */				\
>  	EXCEPTION_PROLOG_0(PACA_EXGEN);					\
>  	__EXCEPTION_PROLOG_1(PACA_EXGEN, extra, vec);			\
> @@ -427,6 +426,7 @@ label##_relon_hv:						\
>  	. = loc;							\
>  	.globl label##_pSeries;						\
>  label##_pSeries:							\
> +	HMT_MEDIUM_PPR_DISCARD;						\
>  	_MASKABLE_EXCEPTION_PSERIES(vec, label,				\
>  				    EXC_STD, SOFTEN_TEST_PR)
>  
> diff --git a/arch/powerpc/kernel/exceptions-64s.S b/arch/powerpc/kernel/exceptions-64s.S
> index 56bd923..574db3f 100644
> --- a/arch/powerpc/kernel/exceptions-64s.S
> +++ b/arch/powerpc/kernel/exceptions-64s.S
> @@ -235,6 +235,7 @@ instruction_access_slb_pSeries:
>  	.globl hardware_interrupt_hv;
>  hardware_interrupt_pSeries:
>  hardware_interrupt_hv:
> +	HMT_MEDIUM_PPR_DISCARD
>  	BEGIN_FTR_SECTION
>  		_MASKABLE_EXCEPTION_PSERIES(0x502, hardware_interrupt,
>  					    EXC_HV, SOFTEN_TEST_HV)
> @@ -254,7 +255,11 @@ hardware_interrupt_hv:
>  	STD_EXCEPTION_PSERIES(0x800, 0x800, fp_unavailable)
>  	KVM_HANDLER_PR(PACA_EXGEN, EXC_STD, 0x800)
>  
> -	MASKABLE_EXCEPTION_PSERIES(0x900, 0x900, decrementer)
> +	. = 0x900
> +	.globl decrementer_pSeries
> +decrementer_pSeries:
> +	_MASKABLE_EXCEPTION_PSERIES(0x900, decrementer, EXC_STD, SOFTEN_TEST_PR)
> +
>  	STD_EXCEPTION_HV(0x980, 0x982, hdecrementer)
>  
>  	MASKABLE_EXCEPTION_PSERIES(0xa00, 0xa00, doorbell_super)
>
Mike Qiu - April 27, 2013, 9:34 a.m.
于 2013/4/26 11:51, Paul Mackerras 写道:
> Building a 64-bit powerpc kernel with PR KVM enabled currently gives
> this error:
>
>    AS      arch/powerpc/kernel/head_64.o
> arch/powerpc/kernel/exceptions-64s.S: Assembler messages:
> arch/powerpc/kernel/exceptions-64s.S:258: Error: attempt to move .org backwards
> make[2]: *** [arch/powerpc/kernel/head_64.o] Error 1
>
> This happens because the MASKABLE_EXCEPTION_PSERIES macro turns into
> 33 instructions, but we only have space for 32 at the decrementer
> interrupt vector (from 0x900 to 0x980).
>
> In the code generated by the MASKABLE_EXCEPTION_PSERIES macro, we
> currently have two instances of the HMT_MEDIUM macro, which has the
> effect of setting the SMT thread priority to medium.  One is the
> first instruction, and is overwritten by a no-op on processors where
> we save the PPR (processor priority register), that is, POWER7 or
> later.  The other is after we have saved the PPR.
>
> In order to reduce the code at 0x900 by one instruction, we omit the
> first HMT_MEDIUM.  On processors without SMT this will have no effect
> since HMT_MEDIUM is a no-op there.  On POWER5 and RS64 machines this
> will mean that the first few instructions take a little longer in the
> case where a decrementer interrupt occurs when the hardware thread is
> running at low SMT priority.  On POWER6 and later machines, the
> hardware automatically boosts the thread priority when a decrementer
> interrupt is taken if the thread priority was below medium, so this
> change won't make any difference.
>
> The alternative would be to branch out of line after saving the CFAR.
> However, that would incur an extra overhead on all processors, whereas
> the approach adopted here only adds overhead on older threaded processors.
>
> Signed-off-by: Paul Mackerras <paulus@samba.org>
> ---
>   arch/powerpc/include/asm/exception-64s.h |    2 +-
>   arch/powerpc/kernel/exceptions-64s.S     |    7 ++++++-
>   2 files changed, 7 insertions(+), 2 deletions(-)
>
> diff --git a/arch/powerpc/include/asm/exception-64s.h b/arch/powerpc/include/asm/exception-64s.h
> index 05e6d2e..8e5fae8 100644
> --- a/arch/powerpc/include/asm/exception-64s.h
> +++ b/arch/powerpc/include/asm/exception-64s.h
> @@ -414,7 +414,6 @@ label##_relon_hv:						\
>   #define SOFTEN_NOTEST_HV(vec)		_SOFTEN_TEST(EXC_HV, vec)
>
>   #define __MASKABLE_EXCEPTION_PSERIES(vec, label, h, extra)		\
> -	HMT_MEDIUM_PPR_DISCARD;						\
>   	SET_SCRATCH0(r13);    /* save r13 */				\
>   	EXCEPTION_PROLOG_0(PACA_EXGEN);					\
>   	__EXCEPTION_PROLOG_1(PACA_EXGEN, extra, vec);			\
> @@ -427,6 +426,7 @@ label##_relon_hv:						\
>   	. = loc;							\
>   	.globl label##_pSeries;						\
>   label##_pSeries:							\
> +	HMT_MEDIUM_PPR_DISCARD;						\
>   	_MASKABLE_EXCEPTION_PSERIES(vec, label,				\
>   				    EXC_STD, SOFTEN_TEST_PR)
>
> diff --git a/arch/powerpc/kernel/exceptions-64s.S b/arch/powerpc/kernel/exceptions-64s.S
> index 56bd923..574db3f 100644
> --- a/arch/powerpc/kernel/exceptions-64s.S
> +++ b/arch/powerpc/kernel/exceptions-64s.S
> @@ -235,6 +235,7 @@ instruction_access_slb_pSeries:
>   	.globl hardware_interrupt_hv;
>   hardware_interrupt_pSeries:
>   hardware_interrupt_hv:
> +	HMT_MEDIUM_PPR_DISCARD
>   	BEGIN_FTR_SECTION
>   		_MASKABLE_EXCEPTION_PSERIES(0x502, hardware_interrupt,
>   					    EXC_HV, SOFTEN_TEST_HV)
> @@ -254,7 +255,11 @@ hardware_interrupt_hv:
>   	STD_EXCEPTION_PSERIES(0x800, 0x800, fp_unavailable)
>   	KVM_HANDLER_PR(PACA_EXGEN, EXC_STD, 0x800)
>
> -	MASKABLE_EXCEPTION_PSERIES(0x900, 0x900, decrementer)
> +	. = 0x900
> +	.globl decrementer_pSeries
> +decrementer_pSeries:
> +	_MASKABLE_EXCEPTION_PSERIES(0x900, decrementer, EXC_STD, SOFTEN_TEST_PR)
> +
>   	STD_EXCEPTION_HV(0x980, 0x982, hdecrementer)
>
>   	MASKABLE_EXCEPTION_PSERIES(0xa00, 0xa00, doorbell_super)
test-by: Mike Qiu <qiudayu@linux.vnet.ibm.com>
It's workable for me. but I just use this patch to compile and boot up 
the machine. not do any performance test:)

Patch

diff --git a/arch/powerpc/include/asm/exception-64s.h b/arch/powerpc/include/asm/exception-64s.h
index 05e6d2e..8e5fae8 100644
--- a/arch/powerpc/include/asm/exception-64s.h
+++ b/arch/powerpc/include/asm/exception-64s.h
@@ -414,7 +414,6 @@  label##_relon_hv:						\
 #define SOFTEN_NOTEST_HV(vec)		_SOFTEN_TEST(EXC_HV, vec)
 
 #define __MASKABLE_EXCEPTION_PSERIES(vec, label, h, extra)		\
-	HMT_MEDIUM_PPR_DISCARD;						\
 	SET_SCRATCH0(r13);    /* save r13 */				\
 	EXCEPTION_PROLOG_0(PACA_EXGEN);					\
 	__EXCEPTION_PROLOG_1(PACA_EXGEN, extra, vec);			\
@@ -427,6 +426,7 @@  label##_relon_hv:						\
 	. = loc;							\
 	.globl label##_pSeries;						\
 label##_pSeries:							\
+	HMT_MEDIUM_PPR_DISCARD;						\
 	_MASKABLE_EXCEPTION_PSERIES(vec, label,				\
 				    EXC_STD, SOFTEN_TEST_PR)
 
diff --git a/arch/powerpc/kernel/exceptions-64s.S b/arch/powerpc/kernel/exceptions-64s.S
index 56bd923..574db3f 100644
--- a/arch/powerpc/kernel/exceptions-64s.S
+++ b/arch/powerpc/kernel/exceptions-64s.S
@@ -235,6 +235,7 @@  instruction_access_slb_pSeries:
 	.globl hardware_interrupt_hv;
 hardware_interrupt_pSeries:
 hardware_interrupt_hv:
+	HMT_MEDIUM_PPR_DISCARD
 	BEGIN_FTR_SECTION
 		_MASKABLE_EXCEPTION_PSERIES(0x502, hardware_interrupt,
 					    EXC_HV, SOFTEN_TEST_HV)
@@ -254,7 +255,11 @@  hardware_interrupt_hv:
 	STD_EXCEPTION_PSERIES(0x800, 0x800, fp_unavailable)
 	KVM_HANDLER_PR(PACA_EXGEN, EXC_STD, 0x800)
 
-	MASKABLE_EXCEPTION_PSERIES(0x900, 0x900, decrementer)
+	. = 0x900
+	.globl decrementer_pSeries
+decrementer_pSeries:
+	_MASKABLE_EXCEPTION_PSERIES(0x900, decrementer, EXC_STD, SOFTEN_TEST_PR)
+
 	STD_EXCEPTION_HV(0x980, 0x982, hdecrementer)
 
 	MASKABLE_EXCEPTION_PSERIES(0xa00, 0xa00, doorbell_super)