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Date: Thu, 15 Mar 2007 13:09:35 -0800
From: "Ulrich Drepper" <drepper@gmail.com>
To: "Nick Piggin" <nickpiggin@yahoo.com.au>
Subject: Re: [PATCH 2/3] FUTEX : introduce private hashtables
Cc: "Eric Dumazet" <dada1@cosmosbay.com>,
       "Andrew Morton" <akpm@linux-foundation.org>,
       "Ingo Molnar" <mingo@elte.hu>, "Andi Kleen" <ak@suse.de>,
       "Ravikiran G Thirumalai" <kiran@scalex86.org>,
       "Shai Fultheim (Shai@scalex86.org)" <shai@scalex86.org>,
       "pravin b shelar" <pravin.shelar@calsoftinc.com>,
       linux-kernel@vger.kernel.org
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On 3/15/07, Nick Piggin <nickpiggin@yahoo.com.au> wrote:
> There should be little contention on the memory in the global hash anyway,
> because we can roughly reduce contention as a factor of hash-size/cacheline-size.
>
> What we will have are cache misses on the global table... but we're going to
> get cache misses on those private tables as well.

I'm thinking about NUMA cases.  If you have private tables for a
process which is pinned to some cluster in a NUMA machine the table is
local to the node.  If you have a global table you cannot optimize
your application for such a situation because at least some of the
pages of the global table are remote.