linux-kernel - Re: [git pull] more SLUB updates for 2.6.25

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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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