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

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Date:	Wed, 30 Mar 2011 07:57:49 +1000
From:	Dave Airlie <airlied@...il.com>
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,
	Daniel Vetter <daniel@...ll.ch>
Subject: Re: GEM-related desktop sluggishness due to linear-time arch_get_unmapped_area_topdown()

On Wed, Mar 30, 2011 at 7:04 AM, Jerome Glisse <j.glisse@...il.com> wrote:
> On Tue, Mar 29, 2011 at 4:26 PM, Daniel Vetter <daniel@...ll.ch> wrote:
>> 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
>
> What i had in mind was something little bit more advance that pwrite,
> somethings that would take width,height,pitch of userpage and would be
> able to perform proper blit. But yes pwrite in intel is kind of
> limited.

TTM has support for userpage binding we just don't use it.

Dave.
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