linux-kernel - Re: [PATCH 0/6] x86: Reduce Memory Usage and Inter-Node message traffic (v2)

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Message-ID: <Pine.SGI.4.56.0708271838210.4349416@kluge.engr.sgi.com>
Date:	Mon, 27 Aug 2007 18:46:12 +0000
From:	Mike Travis <travis@...ulhu.engr.sgi.com>
To:	Andi Kleen <ak@...e.de>
cc:	"Siddha, Suresh B" <suresh.b.siddha@...el.com>, travis@....com,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Christoph Lameter <clameter@....com>
Subject: Re: [PATCH 0/6] x86: Reduce Memory Usage and Inter-Node message
 traffic (v2)



On Sat, 25 Aug 2007, Andi Kleen wrote:

> On Fri, Aug 24, 2007 at 05:50:18PM -0700, Siddha, Suresh B wrote:
> > On Fri, Aug 24, 2007 at 03:26:54PM -0700, travis@....com wrote:
> > > Previous Intro:
> >
> > Thanks for doing this.
> >
> > > In x86_64 and i386 architectures most arrays that are sized
> > > using NR_CPUS lay in local memory on node 0.  Not only will most
> > > (99%?) of the systems not use all the slots in these arrays,
> > > particularly when NR_CPUS is increased to accommodate future
> > > very high cpu count systems, but a number of cache lines are
> > > passed unnecessarily on the system bus when these arrays are
> > > referenced by cpus on other nodes.
> >
> > Can we move cpuinfo_x86 also to per cpu area? Though critical run
>
> I worry how much impact that would be? boot_cpu_data is quite
> widely used.
>

I looked at this and it would be a big memory savings.  But I haven't
yet analyzed the various accesses to verify that we can cleanly move
the structure, and that we don't suffer a bunch of tlb misses because
accesses are primarily from node 0.

More info soon.

Thanks,
Mike
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