[Intel-gfx] [PATCH] drm/i915/gem: Reduce flush_ggtt() from a wait-for-idle to a mere barrier flush

[Chris Wilson]

Quoting Chris Wilson (2019-11-20 13:41:13)
> Since we use barriers, we need only explicitly flush those barriers to
> ensure tha we can reclaim the available ggtt for ourselves. The barrier
> flush was implicit inside the intel_gt_wait_for_idle() -- except because
> we use i915_gem_evict from inside an active timeline during execbuf, we
> could easily end up waiting upon ourselves.
> 
> Fixes: 7936a22dd466 ("drm/i915/gt: Wait for new requests in intel_gt_retire_requests()")
> Fixes: a46bfdc83fee ("drm/i915/gt: Wait for new requests in intel_gt_retire_requests()")
> Testcase: igt/gem_exec_reloc/basic-range
> Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> Cc: Tvrtko Ursulin <tvrtko.ursulin at intel.com>

I think we might as well just revert 7936a22dd466 and take another look
at how to repeat the waits; I'm optimistic that with

commit 1683d24c1470fb47716bd3ccd4e06547eb0ce0ed
Author: Chris Wilson <chris at chris-wilson.co.uk>
Date:   Tue Nov 19 16:25:58 2019 +0000

    drm/i915/gt: Move new timelines to the end of active_list

the problem (e.g. igt/live_late_gt_pm) has mostly evaporated.
-Chris