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

[Sinclair Yeh]

This series:  Reviewed-by: Sinclair Yeh <syeh at vmware.com>

On Thu, Jun 22, 2017 at 12:42:32PM +0200, 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.
> 
>