[Intel-gfx] [RFC] drm/i915 : Reduce the shmem page allocation time by using blitter engines for clearing pages.

[Eric Anholt]

sourab.gupta at intel.com writes:

> From: Sourab Gupta <sourab.gupta at intel.com>
>
> This patch is in continuation of and is dependent on earlier patch
> series to 'reduce the time for which device mutex is kept locked'.
> (http://lists.freedesktop.org/archives/intel-gfx/2014-May/044596.html)

One of userspace's assumptions is that when you allocate a new BO, you
can map it and start writing data into it without needing to wait on the
GPU.  I expect this patch to mostly hurt performance on apps (and I note
that the patch doesn't come with any actual performance data) that get
more stalls as a result.

More importantly, though, it breaks existing userspace that relies on
buffers being idle on allocation, for the unsychronized maps used in
intel_bufferobj_subdata() and
intel_bufferobj_map_range(GL_INVALIDATE_BUFFER_BIT |
GL_UNSYNCHRONIZED_BIT)
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