[Mesa-dev] r600g winsys backend rework

Alex Deucher alexdeucher at gmail.com
Mon Aug 8 16:56:21 PDT 2011

On Sun, Aug 7, 2011 at 5:25 PM, Marek Olšák <maraeo at gmail.com> wrote:
> Hi,
> I have been recently trying to get thread offloading of the CS ioctl
> into r600g in order to reduce the impact of kernel overhead on fps.
> That, unfortunately, requires whole winsys/radeon to be used, because
> even the buffer management (bo_map, bo_wait, bo_busy) must take into
> account that a CS ioctl may be in progress. Besides that, there are
> several possible race conditions in r600g, so instead of rewriting
> r600g and trying to do what winsys/radeon is doing, I decided to
> simply use winsys/radeon.
> What's new in r600g:
> - Thread offloading of the DRM CS ioctl. I expect 0-15% increase in
> performance from that in CPU-bound apps.
> - The new GEM_WAIT ioctl is used to avoid waiting for a buffer when
> possible. (e.g. Mesa may map an index buffer to compute index bounds,
> which shouldn't cause unnecessary waiting now) I have sent the DRM
> patches which add the ioctl to dri-devel.
> - Thread-safety: There are several possible races in r600g. I
> especially don't like radeon_bo::reloc, which may cause pretty ugly
> races if a resource is shared and relocated in multiple contexts.
> winsys/radeon doesn't have that race and also fixes a couple more.
> Hopefully this thread-safeness won't cause performance regressions.
> winsys/radeon can do space checking as well, but we don't use that in r600g yet.
> Performance improvements - I have been able to find a difference with
> these apps:
> Unigine Heaven
> Before: 7.3 fps
> After: 7.6 fps
> Torcs
> Before: 29 fps
> After: 34 fps
> Note that every commit in the r600winsys2 branch has been committed
> without piglit regressions, so that we can bisect through it if
> needed. The net loss is a little over 900 lines of code in r600g. The
> fenced cache buffer manager in r600g has turned out not to be superior
> to pb_cache_bufmgr with the is_buffer_busy hook set, so I removed the
> former too, as the latter is way simpler.
> This new work has been pushed into a new branch r600winsys2 in the
> main Mesa repository, please review/test.

Looks good.  I'll try and run some tests on various hw later this week.

Reviewed-by: Alex Deucher <alexander.deucher at amd.com>

> Marek
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