diff mbox series

[v4] pseries/hotplug-memory: hot-add: skip redundant LMB lookup

Message ID 20200916145122.3408129-1-cheloha@linux.ibm.com (mailing list archive)
State Accepted
Commit 72cdd117c449896c707fc6cfe5b90978160697d0
Headers show
Series [v4] pseries/hotplug-memory: hot-add: skip redundant LMB lookup | expand

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Context Check Description
snowpatch_ozlabs/apply_patch success Successfully applied on branch powerpc/merge (27e2fbcd815a088d7d83c7158f76b6e95ab07c50)
snowpatch_ozlabs/build-ppc64le warning Upstream build failed, couldn't test patch
snowpatch_ozlabs/build-ppc64be warning Upstream build failed, couldn't test patch
snowpatch_ozlabs/build-ppc64e warning Upstream build failed, couldn't test patch
snowpatch_ozlabs/build-pmac32 warning Upstream build failed, couldn't test patch
snowpatch_ozlabs/checkpatch warning total: 0 errors, 1 warnings, 0 checks, 29 lines checked
snowpatch_ozlabs/needsstable success Patch has no Fixes tags

Commit Message

Scott Cheloha Sept. 16, 2020, 2:51 p.m. UTC 
During memory hot-add, dlpar_add_lmb() calls memory_add_physaddr_to_nid()
to determine which node id (nid) to use when later calling __add_memory().

This is wasteful.  On pseries, memory_add_physaddr_to_nid() finds an
appropriate nid for a given address by looking up the LMB containing the
address and then passing that LMB to of_drconf_to_nid_single() to get the
nid.  In dlpar_add_lmb() we get this address from the LMB itself.

In short, we have a pointer to an LMB and then we are searching for
that LMB *again* in order to find its nid.

If we call of_drconf_to_nid_single() directly from dlpar_add_lmb() we
can skip the redundant lookup.  The only error handling we need to
duplicate from memory_add_physaddr_to_nid() is the fallback to the
default nid when drconf_to_nid_single() returns -1 (NUMA_NO_NODE) or
an invalid nid.

Skipping the extra lookup makes hot-add operations faster, especially
on machines with many LMBs.

Consider an LPAR with 126976 LMBs.  In one test, hot-adding 126000
LMBs on an upatched kernel took ~3.5 hours while a patched kernel
completed the same operation in ~2 hours:

Unpatched (12450 seconds):
Sep  9 04:06:31 ltc-brazos1 drmgr[810169]: drmgr: -c mem -a -q 126000
Sep  9 04:06:31 ltc-brazos1 kernel: pseries-hotplug-mem: Attempting to hot-add 126000 LMB(s)
[...]
Sep  9 07:34:01 ltc-brazos1 kernel: pseries-hotplug-mem: Memory at 20000000 (drc index 80000002) was hot-added

Patched (7065 seconds):
Sep  8 21:49:57 ltc-brazos1 drmgr[877703]: drmgr: -c mem -a -q 126000
Sep  8 21:49:57 ltc-brazos1 kernel: pseries-hotplug-mem: Attempting to hot-add 126000 LMB(s)
[...]
Sep  8 23:27:42 ltc-brazos1 kernel: pseries-hotplug-mem: Memory at 20000000 (drc index 80000002) was hot-added

It should be noted that the speedup grows more substantial when
hot-adding LMBs at the end of the drconf range.  This is because we
are skipping a linear LMB search.

To see the distinction, consider smaller hot-add test on the same
LPAR.  A perf-stat run with 10 iterations showed that hot-adding 4096
LMBs completed less than 1 second faster on a patched kernel:

Unpatched:
 Performance counter stats for 'drmgr -c mem -a -q 4096' (10 runs):

        104,753.42 msec task-clock                #    0.992 CPUs utilized            ( +-  0.55% )
             4,708      context-switches          #    0.045 K/sec                    ( +-  0.69% )
             2,444      cpu-migrations            #    0.023 K/sec                    ( +-  1.25% )
               394      page-faults               #    0.004 K/sec                    ( +-  0.22% )
   445,902,503,057      cycles                    #    4.257 GHz                      ( +-  0.55% )  (66.67%)
     8,558,376,740      stalled-cycles-frontend   #    1.92% frontend cycles idle     ( +-  0.88% )  (49.99%)
   300,346,181,651      stalled-cycles-backend    #   67.36% backend cycles idle      ( +-  0.76% )  (50.01%)
   258,091,488,691      instructions              #    0.58  insn per cycle
                                                  #    1.16  stalled cycles per insn  ( +-  0.22% )  (66.67%)
    70,568,169,256      branches                  #  673.660 M/sec                    ( +-  0.17% )  (50.01%)
     3,100,725,426      branch-misses             #    4.39% of all branches          ( +-  0.20% )  (49.99%)

           105.583 +- 0.589 seconds time elapsed  ( +-  0.56% )

Patched:
 Performance counter stats for 'drmgr -c mem -a -q 4096' (10 runs):

        104,055.69 msec task-clock                #    0.993 CPUs utilized            ( +-  0.32% )
             4,606      context-switches          #    0.044 K/sec                    ( +-  0.20% )
             2,463      cpu-migrations            #    0.024 K/sec                    ( +-  0.93% )
               394      page-faults               #    0.004 K/sec                    ( +-  0.25% )
   442,951,129,921      cycles                    #    4.257 GHz                      ( +-  0.32% )  (66.66%)
     8,710,413,329      stalled-cycles-frontend   #    1.97% frontend cycles idle     ( +-  0.47% )  (50.06%)
   299,656,905,836      stalled-cycles-backend    #   67.65% backend cycles idle      ( +-  0.39% )  (50.02%)
   252,731,168,193      instructions              #    0.57  insn per cycle
                                                  #    1.19  stalled cycles per insn  ( +-  0.20% )  (66.66%)
    68,902,851,121      branches                  #  662.173 M/sec                    ( +-  0.13% )  (49.94%)
     3,100,242,882      branch-misses             #    4.50% of all branches          ( +-  0.15% )  (49.98%)

           104.829 +- 0.325 seconds time elapsed  ( +-  0.31% )

This is consistent.  An add-by-count hot-add operation adds LMBs
greedily, so LMBs near the start of the drconf range are considered
first.  On an otherwise idle LPAR with so many LMBs we would expect to
find the LMBs we need near the start of the drconf range, hence the
smaller speedup.

Signed-off-by: Scott Cheloha <cheloha@linux.ibm.com>
---
Changelog:

v1: https://lore.kernel.org/linuxppc-dev/20200910175637.2865160-1-cheloha@linux.ibm.com/

v2:
- Move prototype for of_drconf_to_nid_single() to topology.h.
  Requested by Michael Ellerman.

v3:
- Send the right patch.  v2 is from the wrong branch, my mistake.

v4:
- Fix checkpatch.pl warnings.  Reported by Laurent Dufour.

 arch/powerpc/include/asm/topology.h             | 3 +++
 arch/powerpc/mm/numa.c                          | 2 +-
 arch/powerpc/platforms/pseries/hotplug-memory.c | 6 ++++--
 3 files changed, 8 insertions(+), 3 deletions(-)

Comments

Laurent Dufour Sept. 17, 2020, 2:34 p.m. UTC | #1 
Le 16/09/2020 à 16:51, Scott Cheloha a écrit :
> During memory hot-add, dlpar_add_lmb() calls memory_add_physaddr_to_nid()
> to determine which node id (nid) to use when later calling __add_memory().
> 
> This is wasteful.  On pseries, memory_add_physaddr_to_nid() finds an
> appropriate nid for a given address by looking up the LMB containing the
> address and then passing that LMB to of_drconf_to_nid_single() to get the
> nid.  In dlpar_add_lmb() we get this address from the LMB itself.
> 
> In short, we have a pointer to an LMB and then we are searching for
> that LMB *again* in order to find its nid.
> 
> If we call of_drconf_to_nid_single() directly from dlpar_add_lmb() we
> can skip the redundant lookup.  The only error handling we need to
> duplicate from memory_add_physaddr_to_nid() is the fallback to the
> default nid when drconf_to_nid_single() returns -1 (NUMA_NO_NODE) or
> an invalid nid.
> 
> Skipping the extra lookup makes hot-add operations faster, especially
> on machines with many LMBs.
> 
> Consider an LPAR with 126976 LMBs.  In one test, hot-adding 126000
> LMBs on an upatched kernel took ~3.5 hours while a patched kernel
> completed the same operation in ~2 hours:
> 
> Unpatched (12450 seconds):
> Sep  9 04:06:31 ltc-brazos1 drmgr[810169]: drmgr: -c mem -a -q 126000
> Sep  9 04:06:31 ltc-brazos1 kernel: pseries-hotplug-mem: Attempting to hot-add 126000 LMB(s)
> [...]
> Sep  9 07:34:01 ltc-brazos1 kernel: pseries-hotplug-mem: Memory at 20000000 (drc index 80000002) was hot-added
> 
> Patched (7065 seconds):
> Sep  8 21:49:57 ltc-brazos1 drmgr[877703]: drmgr: -c mem -a -q 126000
> Sep  8 21:49:57 ltc-brazos1 kernel: pseries-hotplug-mem: Attempting to hot-add 126000 LMB(s)
> [...]
> Sep  8 23:27:42 ltc-brazos1 kernel: pseries-hotplug-mem: Memory at 20000000 (drc index 80000002) was hot-added
> 
> It should be noted that the speedup grows more substantial when
> hot-adding LMBs at the end of the drconf range.  This is because we
> are skipping a linear LMB search.
> 
> To see the distinction, consider smaller hot-add test on the same
> LPAR.  A perf-stat run with 10 iterations showed that hot-adding 4096
> LMBs completed less than 1 second faster on a patched kernel:
> 
> Unpatched:
>   Performance counter stats for 'drmgr -c mem -a -q 4096' (10 runs):
> 
>          104,753.42 msec task-clock                #    0.992 CPUs utilized            ( +-  0.55% )
>               4,708      context-switches          #    0.045 K/sec                    ( +-  0.69% )
>               2,444      cpu-migrations            #    0.023 K/sec                    ( +-  1.25% )
>                 394      page-faults               #    0.004 K/sec                    ( +-  0.22% )
>     445,902,503,057      cycles                    #    4.257 GHz                      ( +-  0.55% )  (66.67%)
>       8,558,376,740      stalled-cycles-frontend   #    1.92% frontend cycles idle     ( +-  0.88% )  (49.99%)
>     300,346,181,651      stalled-cycles-backend    #   67.36% backend cycles idle      ( +-  0.76% )  (50.01%)
>     258,091,488,691      instructions              #    0.58  insn per cycle
>                                                    #    1.16  stalled cycles per insn  ( +-  0.22% )  (66.67%)
>      70,568,169,256      branches                  #  673.660 M/sec                    ( +-  0.17% )  (50.01%)
>       3,100,725,426      branch-misses             #    4.39% of all branches          ( +-  0.20% )  (49.99%)
> 
>             105.583 +- 0.589 seconds time elapsed  ( +-  0.56% )
> 
> Patched:
>   Performance counter stats for 'drmgr -c mem -a -q 4096' (10 runs):
> 
>          104,055.69 msec task-clock                #    0.993 CPUs utilized            ( +-  0.32% )
>               4,606      context-switches          #    0.044 K/sec                    ( +-  0.20% )
>               2,463      cpu-migrations            #    0.024 K/sec                    ( +-  0.93% )
>                 394      page-faults               #    0.004 K/sec                    ( +-  0.25% )
>     442,951,129,921      cycles                    #    4.257 GHz                      ( +-  0.32% )  (66.66%)
>       8,710,413,329      stalled-cycles-frontend   #    1.97% frontend cycles idle     ( +-  0.47% )  (50.06%)
>     299,656,905,836      stalled-cycles-backend    #   67.65% backend cycles idle      ( +-  0.39% )  (50.02%)
>     252,731,168,193      instructions              #    0.57  insn per cycle
>                                                    #    1.19  stalled cycles per insn  ( +-  0.20% )  (66.66%)
>      68,902,851,121      branches                  #  662.173 M/sec                    ( +-  0.13% )  (49.94%)
>       3,100,242,882      branch-misses             #    4.50% of all branches          ( +-  0.15% )  (49.98%)
> 
>             104.829 +- 0.325 seconds time elapsed  ( +-  0.31% )
> 
> This is consistent.  An add-by-count hot-add operation adds LMBs
> greedily, so LMBs near the start of the drconf range are considered
> first.  On an otherwise idle LPAR with so many LMBs we would expect to
> find the LMBs we need near the start of the drconf range, hence the
> smaller speedup.
> 
> Signed-off-by: Scott Cheloha <cheloha@linux.ibm.com>

Reviewed-by: Laurent Dufour <ldufour@linux.ibm.com>

> ---
> Changelog:
> 
> v1: https://lore.kernel.org/linuxppc-dev/20200910175637.2865160-1-cheloha@linux.ibm.com/
> 
> v2:
> - Move prototype for of_drconf_to_nid_single() to topology.h.
>    Requested by Michael Ellerman.
> 
> v3:
> - Send the right patch.  v2 is from the wrong branch, my mistake.
> 
> v4:
> - Fix checkpatch.pl warnings.  Reported by Laurent Dufour.
> 
>   arch/powerpc/include/asm/topology.h             | 3 +++
>   arch/powerpc/mm/numa.c                          | 2 +-
>   arch/powerpc/platforms/pseries/hotplug-memory.c | 6 ++++--
>   3 files changed, 8 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/powerpc/include/asm/topology.h b/arch/powerpc/include/asm/topology.h
> index f0b6300e7dd3..ae19b19f9d44 100644
> --- a/arch/powerpc/include/asm/topology.h
> +++ b/arch/powerpc/include/asm/topology.h
> @@ -86,6 +86,9 @@ static inline int cpu_distance(__be32 *cpu1_assoc, __be32 *cpu2_assoc)
> 
>   #endif /* CONFIG_NUMA */
> 
> +struct drmem_lmb;
> +int of_drconf_to_nid_single(struct drmem_lmb *lmb);
> +
>   #if defined(CONFIG_NUMA) && defined(CONFIG_PPC_SPLPAR)
>   extern int find_and_online_cpu_nid(int cpu);
>   #else
> diff --git a/arch/powerpc/mm/numa.c b/arch/powerpc/mm/numa.c
> index 1f61fa2148b5..63507b47164d 100644
> --- a/arch/powerpc/mm/numa.c
> +++ b/arch/powerpc/mm/numa.c
> @@ -430,7 +430,7 @@ static int of_get_assoc_arrays(struct assoc_arrays *aa)
>    * This is like of_node_to_nid_single() for memory represented in the
>    * ibm,dynamic-reconfiguration-memory node.
>    */
> -static int of_drconf_to_nid_single(struct drmem_lmb *lmb)
> +int of_drconf_to_nid_single(struct drmem_lmb *lmb)
>   {
>   	struct assoc_arrays aa = { .arrays = NULL };
>   	int default_nid = NUMA_NO_NODE;
> diff --git a/arch/powerpc/platforms/pseries/hotplug-memory.c b/arch/powerpc/platforms/pseries/hotplug-memory.c
> index 0ea976d1cac4..9a533acf8ad0 100644
> --- a/arch/powerpc/platforms/pseries/hotplug-memory.c
> +++ b/arch/powerpc/platforms/pseries/hotplug-memory.c
> @@ -611,8 +611,10 @@ static int dlpar_add_lmb(struct drmem_lmb *lmb)
> 
>   	block_sz = memory_block_size_bytes();
> 
> -	/* Find the node id for this address. */
> -	nid = memory_add_physaddr_to_nid(lmb->base_addr);
> +	/* Find the node id for this LMB.  Fake one if necessary. */
> +	nid = of_drconf_to_nid_single(lmb);
> +	if (nid < 0 || !node_possible(nid))
> +		nid = first_online_node;
> 
>   	/* Add the memory */
>   	rc = __add_memory(nid, lmb->base_addr, block_sz);
>
Michael Ellerman Oct. 7, 2020, 3:21 a.m. UTC | #2 
On Wed, 16 Sep 2020 09:51:22 -0500, Scott Cheloha wrote:
> During memory hot-add, dlpar_add_lmb() calls memory_add_physaddr_to_nid()
> to determine which node id (nid) to use when later calling __add_memory().
> 
> This is wasteful.  On pseries, memory_add_physaddr_to_nid() finds an
> appropriate nid for a given address by looking up the LMB containing the
> address and then passing that LMB to of_drconf_to_nid_single() to get the
> nid.  In dlpar_add_lmb() we get this address from the LMB itself.
> 
> [...]

Applied to powerpc/next.

[1/1] pseries/hotplug-memory: hot-add: skip redundant LMB lookup
      https://git.kernel.org/powerpc/c/72cdd117c449896c707fc6cfe5b90978160697d0

cheers
Michael Ellerman Oct. 7, 2020, 3:25 a.m. UTC | #3 
On Wed, 16 Sep 2020 09:51:22 -0500, Scott Cheloha wrote:
> During memory hot-add, dlpar_add_lmb() calls memory_add_physaddr_to_nid()
> to determine which node id (nid) to use when later calling __add_memory().
> 
> This is wasteful.  On pseries, memory_add_physaddr_to_nid() finds an
> appropriate nid for a given address by looking up the LMB containing the
> address and then passing that LMB to of_drconf_to_nid_single() to get the
> nid.  In dlpar_add_lmb() we get this address from the LMB itself.
> 
> [...]

Applied to powerpc/next.

[1/1] pseries/hotplug-memory: hot-add: skip redundant LMB lookup
      https://git.kernel.org/powerpc/c/72cdd117c449896c707fc6cfe5b90978160697d0

cheers
diff mbox series

Patch

diff --git a/arch/powerpc/include/asm/topology.h b/arch/powerpc/include/asm/topology.h
index f0b6300e7dd3..ae19b19f9d44 100644
--- a/arch/powerpc/include/asm/topology.h
+++ b/arch/powerpc/include/asm/topology.h
@@ -86,6 +86,9 @@  static inline int cpu_distance(__be32 *cpu1_assoc, __be32 *cpu2_assoc)
 
 #endif /* CONFIG_NUMA */
 
+struct drmem_lmb;
+int of_drconf_to_nid_single(struct drmem_lmb *lmb);
+
 #if defined(CONFIG_NUMA) && defined(CONFIG_PPC_SPLPAR)
 extern int find_and_online_cpu_nid(int cpu);
 #else
diff --git a/arch/powerpc/mm/numa.c b/arch/powerpc/mm/numa.c
index 1f61fa2148b5..63507b47164d 100644
--- a/arch/powerpc/mm/numa.c
+++ b/arch/powerpc/mm/numa.c
@@ -430,7 +430,7 @@  static int of_get_assoc_arrays(struct assoc_arrays *aa)
  * This is like of_node_to_nid_single() for memory represented in the
  * ibm,dynamic-reconfiguration-memory node.
  */
-static int of_drconf_to_nid_single(struct drmem_lmb *lmb)
+int of_drconf_to_nid_single(struct drmem_lmb *lmb)
 {
 	struct assoc_arrays aa = { .arrays = NULL };
 	int default_nid = NUMA_NO_NODE;
diff --git a/arch/powerpc/platforms/pseries/hotplug-memory.c b/arch/powerpc/platforms/pseries/hotplug-memory.c
index 0ea976d1cac4..9a533acf8ad0 100644
--- a/arch/powerpc/platforms/pseries/hotplug-memory.c
+++ b/arch/powerpc/platforms/pseries/hotplug-memory.c
@@ -611,8 +611,10 @@  static int dlpar_add_lmb(struct drmem_lmb *lmb)
 
 	block_sz = memory_block_size_bytes();
 
-	/* Find the node id for this address. */
-	nid = memory_add_physaddr_to_nid(lmb->base_addr);
+	/* Find the node id for this LMB.  Fake one if necessary. */
+	nid = of_drconf_to_nid_single(lmb);
+	if (nid < 0 || !node_possible(nid))
+		nid = first_online_node;
 
 	/* Add the memory */
 	rc = __add_memory(nid, lmb->base_addr, block_sz);