linux-kernel - Re: [PATCH 0/3] FUTEX : new PRIVATE futexes, SMP and NUMA improvements

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Date:	Fri, 16 Mar 2007 11:36:26 +0100
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Eric Dumazet <dada1@...mosbay.com>
Cc:	Nick Piggin <nickpiggin@...oo.com.au>,
	Ulrich Drepper <drepper@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>, Andi Kleen <ak@...e.de>,
	Ravikiran G Thirumalai <kiran@...lex86.org>,
	"Shai Fultheim (Shai@...lex86.org)" <shai@...lex86.org>,
	pravin b shelar <pravin.shelar@...softinc.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/3] FUTEX : new PRIVATE futexes, SMP and NUMA
	improvements

On Fri, 2007-03-16 at 11:30 +0100, Eric Dumazet wrote:
> On Friday 16 March 2007 11:10, Peter Zijlstra wrote:
> 
> > http://programming.kicks-ass.net/kernel-patches/futex-vma-cache/vma_cache.p
> >atch
> 
> Oh thanks
> 
> >
> > > But if it has to walk the vmas (and take mmap_sem), you already loose the
> > > PRIVATE benefit.
> >
> > It doesn't take mmap_sem, I am aware of the problems.
> 
> Yes but the vma_anon() -> vma_cache_find() needs to read 3 cache lines on 
> x86_64 (sizeof(struct vma_cache) = 136)
> and dirty one bit, so it might be more expensive than the mmap_sem ...

I though the cacheline was 128 bytes, but point taken.

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