linux-kernel - Re: [Intel-gfx] [PATCH 3/3] Introduce & use new lightweight SGL iterators

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Message-ID: <573E56AB.9040208@intel.com>
Date:	Fri, 20 May 2016 01:13:31 +0100
From:	Dave Gordon <david.s.gordon@...el.com>
To:	Chris Wilson <chris@...is-wilson.co.uk>
Cc:	Tvrtko Ursulin <tvrtko.ursulin@...ux.intel.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [Intel-gfx] [PATCH 3/3] Introduce & use new lightweight SGL
 iterators

On 19/05/2016 18:27, Chris Wilson wrote:
> On Tue, May 17, 2016 at 01:05:48PM +0100, Dave Gordon wrote:
>> On 17/05/16 11:34, Tvrtko Ursulin wrote:
>>> On 16/05/16 16:19, Dave Gordon wrote:
>>>> The existing for_each_sg_page() iterator is somewhat heavyweight, and is
>>>> limiting i915 driver performance in a few benchmarks. So here we
>>>> introduce somewhat lighter weight iterators, primarily for use with GEM
>>>> objects or other case where we need only deal with whole aligned pages.
>>> Interesting idea, if for nothing then for eliminating the dreaded
>>> st->nents of for_each_sg_page. :)
>>>
>>> Which benchmarks it improves and how much do you know?
>> I know nothing :)
>>
>> But last time I posted some easy-to-use iterators, Chris Wilson said
>> they didn't address his complaint, which was that the existing ones
>> were too slow.
> These aren't very good either... Compared to the sg iters I have:
>
>           gem:exec:fault:1MiB:    -4.32%
>    gem:exec:fault:1MiB:forked:    -5.66%
>          gem:exec:fault:16MiB:   -13.33%
>   gem:exec:fault:16MiB:forked:   -12.03%
>         gem:exec:fault:256MiB:   -15.28%
> gem:exec:fault:256MiB:forked:   -16.98%
>
> (I was really hoping to be able to drop a patch!)

I think you've inlined sg_next() as well? That was the next thing I was 
going to try with these ...
I'll post the version with inline sg_next, but I'm on holiday now so 
won't be around until the end of the month.

.Dave.