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From: Andrew Morton <akpm@osdl.org>
To: Nick Piggin <nickpiggin@yahoo.com.au>
Cc: clameter@engr.sgi.com, kiran@scalex86.org,
	linux-kernel@vger.kernel.org, shai@scalex86.org
Subject: Re: [patch] Cache align futex hash buckets
Date: Tue, 21 Feb 2006 18:08:45 -0800	[thread overview]
Message-ID: <20060221180845.79a44449.akpm@osdl.org> (raw)
In-Reply-To: <43FBB2E8.2020300@yahoo.com.au>

Nick Piggin <nickpiggin@yahoo.com.au> wrote:
>
> Christoph Lameter wrote:
> > On Tue, 21 Feb 2006, Nick Piggin wrote:
> > 
> > 
> >>Ravikiran G Thirumalai wrote:
> >>
> >>>Following change places each element of the futex_queues hashtable on a
> >>>different cacheline.  Spinlocks of adjacent hash buckets lie on the same
> >>>cacheline otherwise.
> >>>
> >>
> >>It does not make sense to add swaths of unused memory into a hashtable for
> >>this purpose, does it?
> > 
> > 
> > It does if you essentially have a 4k cacheline (because you are doing NUMA 
> > in software with multiple PCs....) and transferring control of that 
> > cacheline is comparatively expensive.
> > 
> 
> Instead of 1MB hash with 256 entries in it covering 256 cachelines, you
> have a 1MB hash with 65536(ish) entries covering 256 cachelines.
> 

Good (if accidental point).  Kiran, if you're going to gobble a megabyte,
you might as well use all of it and make the hashtable larger, rather than
just leaving 99% of that memory unused...

  reply	other threads:[~2006-02-22  2:10 UTC|newest]

Thread overview: 22+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2006-02-20 23:32 [patch] Cache align futex hash buckets Ravikiran G Thirumalai
2006-02-20 23:33 ` Andrew Morton
2006-02-20 23:34   ` Andrew Morton
2006-02-21  0:09     ` Ravikiran G Thirumalai
2006-02-21  0:23       ` Andrew Morton
2006-02-21  1:04         ` Ravikiran G Thirumalai
2006-02-21  1:09           ` Andrew Morton
2006-02-21  1:39             ` Ravikiran G Thirumalai
2006-02-21 14:44             ` Andi Kleen
2006-02-21  3:30 ` Nick Piggin
2006-02-21 18:33   ` Christoph Lameter
2006-02-21 23:14     ` Christoph Lameter
2006-02-22  0:40     ` Nick Piggin
2006-02-22  2:08       ` Andrew Morton [this message]
2006-02-22  2:35         ` Ravikiran G Thirumalai
2006-02-22  2:37         ` Nick Piggin
2006-02-22 20:17           ` Ravikiran G Thirumalai
2006-02-22 20:50             ` Andrew Morton
     [not found]               ` <20060223015144.GC3663@localhost.localdomain>
2006-02-23  2:08                 ` Ravikiran G Thirumalai
2006-02-21 20:20   ` Ravikiran G Thirumalai
2006-02-22  0:45     ` Nick Piggin
2006-02-22  2:09       ` Andrew Morton

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