linux-kernel - Re: [PATCH v2] lib/scatterlist: add simple page iterator

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Message-ID: <20130212171305.GB7348@htj.dyndns.org>
Date:	Tue, 12 Feb 2013 09:13:05 -0800
From:	Tejun Heo <tj@...nel.org>
To:	Imre Deak <imre.deak@...el.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org,
	Maxim Levitsky <maximlevitsky@...il.com>,
	Daniel Vetter <daniel.vetter@...ll.ch>,
	linaro-mm-sig@...ts.linaro.org
Subject: Re: [PATCH v2] lib/scatterlist: add simple page iterator

Hello,

On Tue, Feb 12, 2013 at 07:07:20PM +0200, Imre Deak wrote:
> It's the one implemented by sg_miter_{start,stop} in scatterlist.c. It
> also iterates through a scatterlist a page at a time, but it also kmaps
> these pages. Since in our use case we don't need to map the pages we
> needed a solution without this overhead.

I'm not against having non-mapping iterator but please consider that
kmaps are no-ops on many configurations.  It matters only for archs w/
high memory.

> where each entry on the sglist contained 16 consecutive pages. This
> takes ~10% more time for the uninlined version to run. This is a rather
> artificial test and I couldn't come up with something more real-life
> using only the i915 driver's ioctl interface that would show a
> significant change in speed.
> 
> So at least for now I'm ok with just uninlining all the helpers.

Can we reimplement mapping iters using the new ones?

Thanks.

-- 
tejun
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