linux-kernel - Re: GEM-related desktop sluggishness due to linear-time arch_get_unmapped_area

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Message-ID: <20110329202608.GA3454@viiv.ffwll.ch>
Date:	Tue, 29 Mar 2011 22:26:08 +0200
From:	Daniel Vetter <daniel@...ll.ch>
To:	Jerome Glisse <j.glisse@...il.com>
Cc:	Lucas Stach <dev@...xeye.de>, r6144 <rainy6144@...il.com>,
	linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org
Subject: Re: GEM-related desktop sluggishness due to linear-time
 arch_get_unmapped_area_topdown()

On Tue, Mar 29, 2011 at 03:45:34PM -0400, Jerome Glisse wrote:
> Short lived & small bo would definitly doesn't work well for this kind
> of API, it would all be a function of the ioctl cost. But i am not
> sure the drawback would be that big, intel tested with pread/pwrite
> and gived up don't remember why. For the vbo case you describe the
> scheme i was thinking would be : allocate bo and on buffer data call
> upload to the allocated bo using the bind user page feature that would
> mean zero extra copy operation. For the fire forget case of vbo,
> likely somekind of transient buffer would be more appropriate.

Just to clarify: Uploads to linear buffers are all done with pwrite (due
to an api foobar, it's not so great for 2d/tiled stuff). It's amazing how
much faster that is: Switching vbo's from mmpa to pwrite has given a few
percent more fps in openarena in i915g! As long as the chunk you're gonna
write fits into L1 cache, it's probably a net win.
-Daniel
-- 
Daniel Vetter
Mail: daniel@...ll.ch
Mobile: +41 (0)79 365 57 48
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