netdev - Re: [PATCH] percpu: add optimized generic percpu accessors

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Message-Id: <20090127.134747.153565246.davem@davemloft.net>
Date:	Tue, 27 Jan 2009 13:47:47 -0800 (PST)
From:	David Miller <davem@...emloft.net>
To:	cl@...ux-foundation.org
Cc:	tj@...nel.org, rusty@...tcorp.com.au, mingo@...e.hu,
	herbert@...dor.apana.org.au, akpm@...ux-foundation.org,
	hpa@...or.com, brgerst@...il.com, ebiederm@...ssion.com,
	travis@....com, linux-kernel@...r.kernel.org, steiner@....com,
	hugh@...itas.com, netdev@...r.kernel.org,
	mathieu.desnoyers@...ymtl.ca
Subject: Re: [PATCH] percpu: add optimized generic percpu accessors

From: Christoph Lameter <cl@...ux-foundation.org>
Date: Tue, 27 Jan 2009 15:08:57 -0500 (EST)

> On Tue, 27 Jan 2009, Tejun Heo wrote:
> 
> > > later). That's because they use TLB tricks for a static 64k per-cpu
> > > area, but this doesn't scale.  That might not be vital: abandoning
> > > that trick will mean they can't optimise read_percpu/read_percpu_var
> > > etc as much.
> 
> Why wont it scale? this is a separate TLB entry for each processor.

The IA64 per-cpu TLB entry only covers 64k which makes use of it for
dynamic per-cpu stuff out of the question.  That's why it "doesn't
scale"
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