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Message-ID: <47AC04CD.9090407@cosmosbay.com>
Date: Fri, 08 Feb 2008 08:29:17 +0100
From: Eric Dumazet <dada1@...mosbay.com>
To: Nick Piggin <nickpiggin@...oo.com.au>
CC: Christoph Lameter <clameter@....com>,
Linus Torvalds <torvalds@...ux-foundation.org>,
Andrew Morton <akpm@...ux-foundation.org>,
LKML <linux-kernel@...r.kernel.org>, linux-mm@...ck.org
Subject: Re: [git pull] more SLUB updates for 2.6.25
Nick Piggin a écrit :
> On Friday 08 February 2008 13:13, Christoph Lameter wrote:
>> are available in the git repository at:
>>
>> git://git.kernel.org/pub/scm/linux/kernel/git/christoph/vm.git slub-linus
>>
>> (includes the cmpxchg_local fastpath since the cmpxchg_local work
>> by Matheiu is in now, and the non atomic unlock by Nick. Verified that
>> this is not doing any harm after some other patches had been removed.
>
> Ah, good. I think it is always a good thing to be able to remove atomics.
> They place quite a bit of burden on the CPU, especially x86 where it also
> has implicit memory ordering semantics (although x86 can speculatively
> get around much of the problem, it's obviously worse than no restriction)
>
> Even if perhaps some cache coherency or timing quirk makes the non-atomic
> version slower (all else being equal), then I'd still say that the non
> atomic version should be preferred.
>
What about IRQ masking then ?
Many CPU pay high cost for cli/sti pair...
And SLAB/SLUB allocators, even if only used from process context, want to
disable/re-enable interrupts...
I understand kmalloc() want generic pools, but dedicated pools could avoid
this cli/sti
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