Re: [PATCH 06/14] drm/i915: Cancel retire_worker on parking

Chris Wilson
2019-05-02T14:26:45Z

Quoting Tvrtko Ursulin (2019-05-02 15:20:52)
>
> On 02/05/2019 14:33, Chris Wilson wrote:
> > Quoting Tvrtko Ursulin (2019-05-02 14:29:50)
> >>
> >> On 01/05/2019 12:45, Chris Wilson wrote:
> >>> Replace the racy continuation check within retire_work with a definite
> >>> kill-switch on idling. The race was being exposed by gem_concurrent_blit
> >>> where the retire_worker would be terminated too early leaving us
> >>> spinning in debugfs/i915_drop_caches with nothing flushing the
> >>> retirement queue.
> >>>
> >>> Although that the igt is trying to idle from one child while submitting
> >>> from another may be a contributing factor as to why it runs so slowly...
> >>>
> >>> Testcase: igt/gem_concurrent_blit
> >>> Fixes: 79ffac8599c4 ("drm/i915: Invert the GEM wakeref hierarchy")
> >>> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> >>> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
> >>> ---
> >>> drivers/gpu/drm/i915/i915_gem_pm.c | 18 ++++++++++++------
> >>> .../gpu/drm/i915/selftests/mock_gem_device.c | 1 -
> >>> 2 files changed, 12 insertions(+), 7 deletions(-)
> >>>
> >>> diff --git a/drivers/gpu/drm/i915/i915_gem_pm.c b/drivers/gpu/drm/i915/i915_gem_pm.c
> >>> index ae91ad7cb31e..b239b55f84cd 100644
> >>> --- a/drivers/gpu/drm/i915/i915_gem_pm.c
> >>> +++ b/drivers/gpu/drm/i915/i915_gem_pm.c
> >>> @@ -30,15 +30,23 @@ static void idle_work_handler(struct work_struct *work)
> >>> {
> >>> struct drm_i915_private *i915 =
> >>> container_of(work, typeof(*i915), gem.idle_work);
> >>> + bool restart = true;
> >>>
> >>> + cancel_delayed_work_sync(&i915->gem.retire_work);
> >>> mutex_lock(&i915->drm.struct_mutex);
> >>>
> >>
> >> You don't want to run another retire here? Since the retire worker might
> >> have just been canceled I thought you should.
> >
> > Why though? If there are retires outstanding, we won't sleep and want to
> > defer parking until after the next cycle.
>
> In this case what is the point of cancel_delayed_work_*sync* and not
> just the async cancel?

There's an non-sync version? Ah ha!
-Chris