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SubjectRe: [PATCH 1/3 v2] slub: prefetch next freelist pointer in __slab_alloc()
From
2012/7/4 Pekka Enberg <penberg@kernel.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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