linux-kernel - Re: [patch] cache pipe buf page address for non-highmem arch

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Message-ID: <b040c32a0703271106y427d3850y4836ec61ab49942c@mail.gmail.com>
Date:	Tue, 27 Mar 2007 11:06:24 -0700
From:	"Ken Chen" <kenchen@...gle.com>
To:	"Andi Kleen" <andi@...stfloor.org>
Cc:	"Andrew Morton" <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [patch] cache pipe buf page address for non-highmem arch

On 27 Mar 2007 17:01:01 +0200, Andi Kleen <andi@...stfloor.org> wrote:
> What is the problem? You have cache misses on the the hash table
> or are the instructions really an issue on a modern CPU?

It was page_to_pfn() on numa system.  I think it's cache misses on per
node pgdat lookup with node index calculation on each pipe buffer
page.

> e.g. i out of lined virt_to_page to save space, but it could be probably
> inlined again if it was severly time critical.

That would be a problem too, though not showing up in the pipe code path.
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