[Intel-gfx] [PATCH 2/2] drm/i915: Keep the per-object list of VMAs under control

[Chris Wilson]

On Mon, Feb 01, 2016 at 11:00:08AM +0000, Tvrtko Ursulin wrote:
> From: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
> 
> Where objects are shared across contexts and heavy rendering
> is in progress, execlist retired request queue will grow
> unbound until the GPU is idle enough for the retire worker
> to run and call intel_execlists_retire_requests.
> 
> With some workloads, like for example gem_close_race, that
> never happens causing the shared object VMA list to grow to
> epic proportions, and in turn causes retirement call sites to
> spend linearly more and more time walking the obj->vma_list.
> 
> End result is the above mentioned test case taking ten minutes
> to complete and using up more than a GiB of RAM just for the VMA
> objects.
> 
> If we instead trigger the execlist house keeping a bit more
> often, obj->vma_list will be kept in check by the virtue of
> context cleanup running and zapping the inactive VMAs.
> 
> This makes the test case an order of magnitude faster and brings
> memory use back to normal.
> 
> This also makes the code more self-contained since the
> intel_execlists_retire_requests call-site is now in a more
> appropriate place and implementation leakage is somewhat
> reduced.

However, this then causes a perf regression since we unpin the contexts
too frequently and do not have any mitigation in place yet.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre