From: Daniel Vetter <daniel@ffwll.ch>
To: Rahul Sharma <r.sh.open@gmail.com>
Cc: Rahul Sharma <rahul.sharma@samsung.com>,
"joshi@samsung.com" <joshi@samsung.com>,
"dri-devel@lists.freedesktop.org"
<dri-devel@lists.freedesktop.org>
Subject: Re: [PATCH] drm: modify pages_to_sg prime helper to create optimized SG table
Date: Thu, 31 Jan 2013 13:17:35 +0100 [thread overview]
Message-ID: <CAKMK7uHrXxeJs0pm=msn-7YN6jLiJ79hg0nXQAimEmh3RSrjgA@mail.gmail.com> (raw)
In-Reply-To: <CAPdUM4MGQ6YnXqgasEBiT2VynR56wtK1_kkMcG9X2wo59bXEEw@mail.gmail.com>
On Thu, Jan 31, 2013 at 12:54 PM, Rahul Sharma <r.sh.open@gmail.com> wrote:
> I have parsed the related code and it looks fine to me. I couldn't find
> any code section, expecting sg-tables with single-page sgl entries. I
> just want to ensure again that it doesn't cause any side effects on
> various platforms.
Just chatted with Chris Wilson on our team, and at last i915.ko _has_
code paths which rely on this. See the reloc handling offset
computations in i915_gem_execbuf.c. I haven't checked
ttm/radeon/nouveau/vmwgfx simply because I don't have the time right
now, and I know that doing this carefully will blow through a few
days. So this patch will break prime buffer sharing on the desktop.
The other thing is that only doing sg entry coalescing for
prime/dma_buf will lead to a QA problem, since all the normal sg
tables still have a 1:1 relationship. So imo the right way to move
forward with this is to convert the various sg table constructors in
i915/ttm/radeon/nouveau/... over to coalesce pages. This allows us to
fix any fallout step-by-step.
Then, once each driver is ready for this, we can merge your patch.
>> For the patch itself I think there's now a generic pages_to_sg helper
>> in the dma core which does exactly what you want it to do. I can dig
>> it out if you can't find it.
>>
>
> Sorry, I din't get this part. Please elaborate a bit.
See sg_alloc_table_from_pages in lib/scatterlist.c introduced with:
commit efc42bc98058a36d761b16a114823db1a902ed05
Author: Tomasz Stanislawski <t.stanislaws@samsung.com>
Date: Mon Jun 18 09:25:01 2012 +0200
scatterlist: add sg_alloc_table_from_pages function
Cheers, Daniel
--
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch
next prev parent reply other threads:[~2013-01-31 12:17 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-01-28 13:38 [PATCH] drm: modify pages_to_sg prime helper to create optimized SG table Rahul Sharma
2013-01-29 17:10 ` Aaron Plattner
2013-01-31 8:38 ` Rahul Sharma
2013-01-31 8:53 ` Daniel Vetter
2013-01-31 11:54 ` Rahul Sharma
2013-01-31 12:17 ` Daniel Vetter [this message]
2013-01-31 13:26 ` Rahul Sharma
2013-01-31 14:24 ` Daniel Vetter
2013-03-19 9:09 ` Daniel Vetter
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