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From: Ben Widawsky <ben@bwidawsk.net>
To: Keith Packard <keithp@keithp.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>, intel-gfx@lists.freedesktop.org
Subject: Re: [PATCH 3/6] drm/i915: Support write only mappings
Date: Tue, 20 Sep 2011 05:37:45 +0000	[thread overview]
Message-ID: <20110920053745.GA11743@cloud01> (raw)
In-Reply-To: <yun39frhjdg.fsf@aiko.keithp.com>


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On Mon, Sep 19, 2011 at 10:29:15PM -0700, Keith Packard wrote:
> On Mon, 19 Sep 2011 21:25:03 -0700, Ben Widawsky <ben@bwidawsk.net> wrote:
> > When doing a GTT mapping, the pages are not backed until taking a fault.
> > If we know that the object is write only, when the fault happens we do not need
> > to make the pages coherent with the CPU.  This allows for semi fast prefaults
> > to occur in libdrm at map time.
> 
> Every time I see this stuff, I get confused by the term
> 'write-only'. Reading through the code, I remind myself that what you're
> actually promising is that any CPU accesses to the object will not
> overlap any potential writes by the GPU. The CPU could be reading or
> writing, it really doesn't matter.

I think of it as, we (libdrm + kernel) promise that the buffer is not
guaranteed to be coherent with the GPU. Mesa/client is who should be
making the promise to not write to a part of the buffer that the GPU may
be accessing.
> 
> Really what you want is a kernel call that does everything except block
> on the GPU, right?

Yes, exactly.

Ben

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  reply	other threads:[~2011-09-20  5:34 UTC|newest]

Thread overview: 28+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2011-09-20  4:25 [PATCH 1/6] RFCish: write only mappings (aka non-blocking) Ben Widawsky
2011-09-20  4:25 ` [PATCH 1/6] drm/i915: object CPU flush interface Ben Widawsky
2011-09-20  4:25 ` [PATCH 2/6] drm/i915: write only object tracking Ben Widawsky
2011-09-20  4:25 ` [PATCH 3/6] drm/i915: Support write only mappings Ben Widawsky
2011-09-20  5:29   ` Keith Packard
2011-09-20  5:37     ` Ben Widawsky [this message]
2011-09-20  8:30   ` Chris Wilson
2011-09-20  4:25 ` [PATCH 4/6] intel: write only map support Ben Widawsky
2011-09-20  4:25 ` [PATCH 5/6] write-only mappings Ben Widawsky
2011-09-20  4:25 ` [PATCH 6/6] intel: use write only maps for MapRangeBuffer Ben Widawsky
2011-09-20 11:06 ` [PATCH 1/6] RFCish: write only mappings (aka non-blocking) Daniel Vetter
2011-09-20 17:17   ` Eric Anholt
2011-09-20 19:19     ` Daniel Vetter
2011-09-21  8:19       ` [PATCH] intel: non-blocking mmaps on the cheap Daniel Vetter
2011-09-21 18:11         ` Eric Anholt
2011-09-21 19:19           ` Daniel Vetter
2011-09-22  1:47             ` [PATCH cont'd] " Ben Widawsky
2011-09-22  1:47               ` [PATCH] drm/i915: ioctl to query a bo's cache level Ben Widawsky
2011-09-22  7:35                 ` Daniel Vetter
2011-09-22 15:36                   ` Ben Widawsky
2011-09-22 15:49                     ` Chris Wilson
2011-09-22  1:47               ` [PATCH] on top of daniel Ben Widawsky
2011-09-22  7:39                 ` Daniel Vetter
2011-09-22  7:33               ` [PATCH cont'd] intel: non-blocking mmaps on the cheap Daniel Vetter
2011-09-20 21:16   ` [PATCH 1/6] RFCish: write only mappings (aka non-blocking) Chris Wilson
2011-09-21  7:02     ` Daniel Vetter
2011-09-20 22:19   ` Ben Widawsky
2011-09-21  7:07     ` Daniel Vetter

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