linux-kernel - Re: [PATCH 1/3 v2] slub: prefetch next freelist pointer in __slab

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Date:	Wed, 4 Jul 2012 23:30:14 +0900
From:	JoonSoo Kim <js1304@...il.com>
To:	Pekka Enberg <penberg@...nel.org>
Cc:	Christoph Lameter <cl@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Eric Dumazet <eric.dumazet@...il.com>
Subject: Re: [PATCH 1/3 v2] slub: prefetch next freelist pointer in __slab_alloc()

2012/7/4 Pekka Enberg <penberg@...nel.org>:
> Well, can you show improvement in any benchmark or workload?
> Prefetching is not always an obvious win and the reason we merged
> Eric's patch was that he was able to show an improvement in hackbench.

I thinks that this patch is perfectly same effect as Eric's patch, so
doesn't include benchmark result.
Eric's patch which add "prefetch instruction" in fastpath works for
second ~ last object of cpu slab.
This patch which add "prefetch instrunction" in slowpath works for
first object of cpu slab.

But, I do test "./perf stat -r 20 ./hackbench 50 process 4000 >
/dev/null" and gain following outputs.

***** vanilla *****

 Performance counter stats for './hackbench 50 process 4000' (20 runs):

     114189.571311 task-clock                #    7.924 CPUs utilized
          ( +-  0.29% )
         2,978,515 context-switches          #    0.026 M/sec
          ( +-  3.45% )
           102,635 CPU-migrations            #    0.899 K/sec
          ( +-  5.63% )
           123,948 page-faults               #    0.001 M/sec
          ( +-  0.16% )
   422,477,120,134 cycles                    #    3.700 GHz
          ( +-  0.29% )
   <not supported> stalled-cycles-frontend
   <not supported> stalled-cycles-backend
   251,943,851,074 instructions              #    0.60  insns per
cycle          ( +-  0.14% )
    46,214,207,979 branches                  #  404.715 M/sec
          ( +-  0.15% )
       215,342,095 branch-misses             #    0.47% of all
branches          ( +-  0.53% )

      14.409990448 seconds time elapsed
          ( +-  0.30% )

 Performance counter stats for './hackbench 50 process 4000' (20 runs):

     114576.053284 task-clock                #    7.921 CPUs utilized
          ( +-  0.35% )
         2,810,138 context-switches          #    0.025 M/sec
          ( +-  3.21% )
            85,641 CPU-migrations            #    0.747 K/sec
          ( +-  5.05% )
           124,299 page-faults               #    0.001 M/sec
          ( +-  0.18% )
   423,906,539,517 cycles                    #    3.700 GHz
          ( +-  0.35% )
   <not supported> stalled-cycles-frontend
   <not supported> stalled-cycles-backend
   251,354,351,283 instructions              #    0.59  insns per
cycle          ( +-  0.13% )
    46,098,601,012 branches                  #  402.341 M/sec
          ( +-  0.13% )
       213,448,657 branch-misses             #    0.46% of all
branches          ( +-  0.50% )

      14.464325969 seconds time elapsed
          ( +-  0.34% )


***** patch applied *****

 Performance counter stats for './hackbench 50 process 4000' (20 runs):

     112935.199731 task-clock                #    7.926 CPUs utilized
          ( +-  0.29% )
         2,810,157 context-switches          #    0.025 M/sec
          ( +-  2.95% )
           104,278 CPU-migrations            #    0.923 K/sec
          ( +-  6.83% )
           123,999 page-faults               #    0.001 M/sec
          ( +-  0.17% )
   417,834,406,420 cycles                    #    3.700 GHz
          ( +-  0.29% )
   <not supported> stalled-cycles-frontend
   <not supported> stalled-cycles-backend
   251,291,523,926 instructions              #    0.60  insns per
cycle          ( +-  0.11% )
    46,083,091,476 branches                  #  408.049 M/sec
          ( +-  0.12% )
       213,714,228 branch-misses             #    0.46% of all
branches          ( +-  0.43% )

      14.248980376 seconds time elapsed
          ( +-  0.29% )

 Performance counter stats for './hackbench 50 process 4000' (20 runs):

     113640.944855 task-clock                #    7.926 CPUs utilized
          ( +-  0.28% )
         2,776,983 context-switches          #    0.024 M/sec
          ( +-  5.66% )
            95,962 CPU-migrations            #    0.844 K/sec
          ( +- 10.69% )
           123,849 page-faults               #    0.001 M/sec
          ( +-  0.15% )
   420,446,572,595 cycles                    #    3.700 GHz
          ( +-  0.28% )
   <not supported> stalled-cycles-frontend
   <not supported> stalled-cycles-backend
   251,174,259,429 instructions              #    0.60  insns per
cycle          ( +-  0.21% )
    46,060,683,039 branches                  #  405.318 M/sec
          ( +-  0.23% )
       213,480,999 branch-misses             #    0.46% of all
branches          ( +-  0.75% )

      14.336843534 seconds time elapsed
          ( +-  0.28% )
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