From: Andrew Morton <akpm@osdl.org>
To: James Cloos <cloos@jhcloos.com>
Cc: linux-kernel@vger.kernel.org, david@gibson.dropbear.id.au
Subject: Re: MAP_SHARED bizarrely slow
Date: Wed, 27 Oct 2004 01:06:59 -0700 [thread overview]
Message-ID: <20041027010659.15ec7e90.akpm@osdl.org> (raw)
In-Reply-To: <m3u0sgiq0b.fsf@lugabout.cloos.reno.nv.us>
James Cloos <cloos@jhcloos.com> wrote:
>
> >>>>> "David" == David Gibson <david@gibson.dropbear.id.au> writes:
>
> David> http://www.ozlabs.org/people/dgibson/maptest.tar.gz
>
> David> On a number of machines I've tested - both ppc64 and x86 - the
> David> SHARED version is consistently and significantly (50-100%)
> David> slower than the PRIVATE version.
>
> Just gave it a test on my laptop and server. Both are p3. The
> laptop is under heavier mem pressure; the server has just under
> a gig with most free/cache/buff. Laptop is still running 2.6.7
> whereas the server is bk as of 2004-10-24.
>
> Buth took about 11 seconds for the private and around 30 seconds
> for the shared tests.
>
I get the exact opposite, on a P4:
vmm:/home/akpm/maptest> time ./mm-sharemmap
./mm-sharemmap 10.81s user 0.05s system 100% cpu 10.855 total
vmm:/home/akpm/maptest> time ./mm-sharemmap
./mm-sharemmap 11.04s user 0.05s system 100% cpu 11.086 total
vmm:/home/akpm/maptest> time ./mm-privmmap
./mm-privmmap 26.91s user 0.02s system 100% cpu 26.903 total
vmm:/home/akpm/maptest> time ./mm-privmmap
./mm-privmmap 26.89s user 0.02s system 100% cpu 26.894 total
vmm:/home/akpm/maptest> uname -a
Linux vmm 2.6.10-rc1-mm1 #14 SMP Tue Oct 26 23:23:23 PDT 2004 i686 i686 i386 GNU/Linux
It's all user time so I can think of no reason apart from physical page
allocation order causing additional TLB reloads in one case. One is using
anonymous pages and the other is using shmem-backed pages, although I can't
think why that would make a difference.
Let's back out the no-buddy-bitmap patches:
vmm:/home/akpm/maptest> time ./mm-sharemmap
./mm-sharemmap 12.01s user 0.06s system 99% cpu 12.087 total
vmm:/home/akpm/maptest> time ./mm-sharemmap
./mm-sharemmap 12.56s user 0.05s system 100% cpu 12.607 total
vmm:/home/akpm/maptest> time ./mm-privmmap
./mm-privmmap 26.74s user 0.03s system 99% cpu 26.776 total
vmm:/home/akpm/maptest> time ./mm-privmmap
./mm-privmmap 26.66s user 0.02s system 100% cpu 26.674 total
much the same.
Backing out "[PATCH] tweak the buddy allocator for better I/O merging" from
June 24 makes no difference.
next prev parent reply other threads:[~2004-10-27 8:09 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2004-10-27 6:45 MAP_SHARED bizarrely slow David Gibson
2004-10-27 7:23 ` James Cloos
2004-10-27 7:59 ` David Gibson
2004-10-28 4:38 ` Ian Wienand
2004-10-27 8:06 ` Andrew Morton [this message]
2004-10-27 8:20 ` David Gibson
2004-10-27 8:30 ` James Cloos
2004-10-27 20:54 ` Bill Davidsen
2004-10-28 1:16 ` David Gibson
2004-10-28 5:54 ` dean gaudet
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