[Mesa-dev] [PATCH 0/5] dri3, gallium: Correctness and performance fixes

[Brian Paul]

On 06/28/2017 11:07 AM, Thomas Hellstrom wrote:
> On 06/22/2017 12:42 PM, Thomas Hellstrom wrote:
>> A patch series that deals with dri3 correctness- and performance fixes.
>>
>> The corectness fixes attempts to deal with the fact that we need to
>> wait for
>> all pending swapbuffers before we touch the front buffer. Otherwise a
>> front buffer change may be overwritten by a pending swapbuffer when it
>> was actually intended to be drawn *after* the swapbuffer. Also a post
>> swapbuffer front read could actually occur *before* the swapbuffer.
>>
>> Patch 1 deals with the dri3 internal synchronization. All frontbuffer
>> accesses introduce a "swapbuffer barrier" to order with respect to
>> pending swapbuffers.
>> The exception is _WaitX because if we call _WaitX we're ordering with
>> respect to X rendering and if there are pending swapbuffers, an
>> application
>> would already have called _WaitGL to be able to do the X rendering
>> correctly,
>> and _WaitGL is ordering with respect to pending swapbuffers. This patch
>> fixes the piglit copysubbuffer test.
>>
>> Patch 2 to 4 deals with having glFinish() order with respect to pending
>> swapbuffers. The behaviour is actually not correct in that it doesn't
>> wait
>> for the pending swapbuffers to complete, but a user shouldn't be able to
>> tell the difference. This patch series is motivated by the fact that the
>> glXWaitGL man page states that glFinish() can be used instead of
>> glXWaitGL,
>> and without this series it can't. The functionality is only
>> implemented for
>> gallium. Other drivers need to provide their own implementation. Ideally
>> we should have accomplished this without the dri interface changes by
>> calling an unconditional flush_frontbuffer, but at least the gallium
>> flush_frontbuffer implementation is relying on us having a fake front
>> which
>> is not always the case.
>>
>> Patch 5 replaces the back-to-fake-front full buffer copies with a swap
>> during swapbuffers. Should be saving a lot of work when we actually
>> have a
>> fake front. There were some conserns raised when this was posted as an
>> RFC
>> that the separate-server-gpu case would be broken as well as the buffer
>> age functionality. I've audited the code and I think that's not the case.
>> The piglit buffer age test still reports a pass after this change. The
>> separate-server-gpu case I guess needs additional testing.
>>
>> Tested wih piglit -quick without regressions.
>
> Hi!
>
> Patches 1,2 and 5 are still unreviewed. It would be good to have at
> least a pair of extra eyes on them.

Looks like Emil had an EGL concern with patch 5.  Otherwise, I'm not a 
DRI3 expert but the code looks OK to me.

Reviewed-by: Brian Paul <brianp at vmware.com>