From: Pekka Enberg <penberg@kernel.org>
To: JoonSoo Kim <js1304@gmail.com>
Cc: Christoph Lameter <cl@linux-foundation.org>,
linux-kernel@vger.kernel.org, linux-mm@kvack.org,
Eric Dumazet <eric.dumazet@gmail.com>,
David Rientjes <rientjes@google.com>
Subject: Re: [PATCH 1/3 v2] slub: prefetch next freelist pointer in __slab_alloc()
Date: Wed, 4 Jul 2012 18:08:18 +0300 [thread overview]
Message-ID: <CAOJsxLGBxeu2sE-wDT+YNyVipmXiPj7Gvmmdo-0zGmJObp2zxg@mail.gmail.com> (raw)
In-Reply-To: <CAAmzW4OdDhn5C_vfMhu3ejzzcXmCCt6r0h=nXUqKJaNYZxg8Bw@mail.gmail.com>
> 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.
On Wed, Jul 4, 2012 at 5:30 PM, JoonSoo Kim <js1304@gmail.com> wrote:
> 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.
Prefetching can also have negative effect on overall performance:
http://lwn.net/Articles/444336/
> 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% )
That doesn't seem like that obvious win to me... Eric, Christoph?
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next prev parent reply other threads:[~2012-07-04 15:08 UTC|newest]
Thread overview: 37+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <yes>
2012-06-08 17:23 ` [PATCH 1/4] slub: change declare of get_slab() to inline at all times Joonsoo Kim
2012-06-08 17:23 ` [PATCH 2/4] slub: use __cmpxchg_double_slab() at interrupt disabled place Joonsoo Kim
2012-06-08 17:23 ` [PATCH 3/4] slub: refactoring unfreeze_partials() Joonsoo Kim
2012-06-20 7:19 ` Pekka Enberg
2012-06-08 17:23 ` [PATCH 4/4] slub: deactivate freelist of kmem_cache_cpu all at once in deactivate_slab() Joonsoo Kim
2012-06-08 19:04 ` Christoph Lameter
2012-06-10 10:27 ` JoonSoo Kim
2012-06-22 18:34 ` JoonSoo Kim
2012-06-08 19:02 ` [PATCH 1/4] slub: change declare of get_slab() to inline at all times Christoph Lameter
2012-06-09 15:57 ` JoonSoo Kim
2012-06-11 15:04 ` Christoph Lameter
2012-06-22 18:22 ` [PATCH 1/3] slub: prefetch next freelist pointer in __slab_alloc() Joonsoo Kim
2012-06-22 18:22 ` [PATCH 2/3] slub: reduce failure of this_cpu_cmpxchg in put_cpu_partial() after unfreezing Joonsoo Kim
2012-07-04 13:05 ` Pekka Enberg
2012-07-05 14:20 ` Christoph Lameter
2012-08-16 7:06 ` Pekka Enberg
2012-06-22 18:22 ` [PATCH 3/3] slub: release a lock if freeing object with a lock is failed in __slab_free() Joonsoo Kim
2012-07-04 13:10 ` Pekka Enberg
2012-07-04 14:48 ` JoonSoo Kim
2012-07-05 14:26 ` Christoph Lameter
2012-07-06 14:19 ` JoonSoo Kim
2012-07-06 14:34 ` Christoph Lameter
2012-07-06 14:59 ` JoonSoo Kim
2012-07-06 15:10 ` Christoph Lameter
2012-07-08 16:19 ` JoonSoo Kim
2012-06-22 18:45 ` [PATCH 1/3 v2] slub: prefetch next freelist pointer in __slab_alloc() Joonsoo Kim
2012-07-04 12:58 ` JoonSoo Kim
2012-07-04 13:00 ` Pekka Enberg
2012-07-04 14:30 ` JoonSoo Kim
2012-07-04 15:08 ` Pekka Enberg [this message]
2012-07-04 15:26 ` Eric Dumazet
2012-07-04 15:48 ` JoonSoo Kim
2012-07-04 16:15 ` Eric Dumazet
2012-07-04 16:24 ` JoonSoo Kim
2012-07-04 15:45 ` JoonSoo Kim
2012-07-04 15:59 ` Pekka Enberg
2012-07-04 16:04 ` JoonSoo Kim
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