From: Joonsoo Kim <iamjoonsoo.kim@lge.com>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: Dave Hansen <dave@sr71.net>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org,
penberg@kernel.org, cl@linux-foundation.org
Subject: Re: [PATCH 0/9] re-shrink 'struct page' when SLUB is on.
Date: Mon, 6 Jan 2014 13:32:37 +0900 [thread overview]
Message-ID: <20140106043237.GE696@lge.com> (raw)
In-Reply-To: <20140103141816.20ef2a24c8adffae040e53dc@linux-foundation.org>
On Fri, Jan 03, 2014 at 02:18:16PM -0800, Andrew Morton wrote:
> On Fri, 03 Jan 2014 10:01:47 -0800 Dave Hansen <dave@sr71.net> wrote:
>
> > This is a minor update from the last version. The most notable
> > thing is that I was able to demonstrate that maintaining the
> > cmpxchg16 optimization has _some_ value.
> >
> > Otherwise, the code changes are just a few minor cleanups.
> >
> > ---
> >
> > SLUB depends on a 16-byte cmpxchg for an optimization which
> > allows it to not disable interrupts in its fast path. This
> > optimization has some small but measurable benefits:
> >
> > http://lkml.kernel.org/r/52B345A3.6090700@sr71.net
>
> So really the only significant benefit from the cmpxchg16 is with
> cache-cold eight-byte kmalloc/kfree? 8% faster in this case? But with
> cache-hot kmalloc/kfree the benefit of cmpxchg16 is precisely zero.
Hello,
I guess that cmpxchg16 is not used in this cache-hot kmalloc/kfree test,
because kfree would be done in free fast-path. In this case,
this_cpu_cmpxchg_double() would be called, so you cannot find any effect
of cmpxchg16.
Thanks.
>
> This is really weird and makes me suspect a measurement glitch.
>
> Even if this 8% is real, it's unclear that it's worth all the
> complexity the cmpxchg16 adds.
>
> It would be really useful (hint :)) if we were to know exactly where
> that 8% is coming from - perhaps it's something which is not directly
> related to the cmpxchg16, and we can fix it separately.
>
>
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next prev parent reply other threads:[~2014-01-06 4:32 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-01-03 18:01 [PATCH 0/9] re-shrink 'struct page' when SLUB is on Dave Hansen
2014-01-03 18:01 ` [PATCH 1/9] mm: slab/slub: use page->list consistently instead of page->lru Dave Hansen
2014-01-03 18:01 ` [PATCH 2/9] mm: blk-mq: uses page->list incorrectly Dave Hansen
2014-01-03 18:01 ` [PATCH 3/9] mm: page->pfmemalloc only used by slab/skb Dave Hansen
2014-01-03 18:01 ` [PATCH 4/9] mm: slabs: reset page at free Dave Hansen
2014-01-03 18:01 ` [PATCH 5/9] mm: rearrange struct page Dave Hansen
2014-01-03 18:01 ` [PATCH 6/9] mm: slub: rearrange 'struct page' fields Dave Hansen
2014-01-03 18:02 ` [PATCH 7/9] mm: slub: abstract out double cmpxchg option Dave Hansen
2014-01-03 18:02 ` [PATCH 8/9] mm: slub: remove 'struct page' alignment restrictions Dave Hansen
2014-01-03 18:02 ` [PATCH 9/9] mm: slub: cleanups after code churn Dave Hansen
2014-01-03 22:18 ` [PATCH 0/9] re-shrink 'struct page' when SLUB is on Andrew Morton
2014-01-06 4:32 ` Joonsoo Kim [this message]
2014-01-10 20:52 ` Dave Hansen
2014-01-10 23:39 ` Andrew Morton
2014-01-10 23:42 ` Dave Hansen
2014-01-11 9:26 ` Pekka Enberg
2014-01-12 0:55 ` Christoph Lameter
2014-01-13 1:44 ` Joonsoo Kim
2014-01-13 3:36 ` Davidlohr Bueso
2014-01-13 13:46 ` Fengguang Wu
2014-01-13 15:42 ` Dave Hansen
2014-01-13 17:16 ` Dave Hansen
2014-01-14 20:07 ` Christoph Lameter
2014-01-14 22:05 ` Dave Hansen
2014-01-16 16:44 ` Christoph Lameter
2014-01-16 17:08 ` Dave Hansen
2014-01-16 18:26 ` Christoph Lameter
2014-01-14 17:40 ` Christoph Lameter
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