On Thu, 2016-11-03 at 21:14 +0000, Chris Wilson wrote: > On Thu, Nov 03, 2016 at 10:57:23PM +0200, Imre Deak wrote: > > On Thu, 2016-11-03 at 18:59 +0000, Chris Wilson wrote: > > > On Thu, Nov 03, 2016 at 06:19:37PM +0200, Imre Deak wrote: > > > > We assume that the GPU is idle once receiving the seqno via the last > > > > request's user interrupt. In execlist mode the corresponding context > > > > completed interrupt can be delayed though and until this latter > > > > interrupt arrives we consider the request to be pending on the ELSP > > > > submit port. This can cause a problem during system suspend where this > > > > last request will be seen by the resume code as still pending. Such > > > > pending requests are normally replayed after a GPU reset, but during > > > > resume we reset both SW and HW tracking of the ring head/tail pointers, > > > > so replaying the pending request with its stale tale pointer will leave > > > > the ring in an inconsistent state. A subsequent request submission can > > > > lead then to the GPU executing from uninitialized area in the ring > > > > behind the above stale tail pointer. > > > > > > > > Fix this by making sure any pending request on the ELSP port is > > > > completed before suspending. I used a polling wait since the completion > > > > time I measured was <1ms and since normally we only need to wait during > > > > system suspend. GPU idling during runtime suspend is scheduled with a > > > > delay (currently 50-100ms) after the retirement of the last request at > > > > which point the context completed interrupt must have arrived already. > > > > > > > > The chance of this bug was increased by > > > > > > > > commit 1c777c5d1dcdf8fa0223fcff35fb387b5bb9517a > > > > Author: Imre Deak <imre.deak@xxxxxxxxx> > > > > Date: Wed Oct 12 17:46:37 2016 +0300 > > > > > > > > drm/i915/hsw: Fix GPU hang during resume from S3-devices state > > > > > > > > but it could happen even without the explicit GPU reset, since we > > > > disable interrupts afterwards during the suspend sequence. > > > > > > > > Cc: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx> > > > > Cc: Mika Kuoppala <mika.kuoppala@xxxxxxxxx> > > > > Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=98470 > > > > Signed-off-by: Imre Deak <imre.deak@xxxxxxxxx> > > > > --- > > > > drivers/gpu/drm/i915/i915_gem.c | 3 +++ > > > > drivers/gpu/drm/i915/intel_lrc.c | 12 ++++++++++++ > > > > drivers/gpu/drm/i915/intel_lrc.h | 1 + > > > > 3 files changed, 16 insertions(+) > > > > > > > > diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c > > > > index 1f995ce..5ff02b5 100644 > > > > --- a/drivers/gpu/drm/i915/i915_gem.c > > > > +++ b/drivers/gpu/drm/i915/i915_gem.c > > > > @@ -2766,6 +2766,9 @@ i915_gem_idle_work_handler(struct work_struct *work) > > > > if (dev_priv->gt.active_requests) > > > > goto out_unlock; > > > > > > > > + if (i915.enable_execlists) > > > > + intel_lr_wait_engines_idle(dev_priv); > > > > > > Idle work handler... So runtime suspend. > > > Anyway this is not an ideal place for a stall under struct_mutex (even if > > > 16x10us, it's the principle!). > > > > During runtime suspend this won't add any overhead since the context > > done interrupt happened already (unless there is a bug somewhere else). > > Where is that guaranteed? I thought we only serialised with the pm > interrupts. Remember this happens before rpm suspend, since > gem_idle_work_handler is responsible for dropping the GPU wakelock. I meant that the 100msec after the last request signals completion and this handler is scheduled is normally enough for the context complete interrupt to get delivered. But yea, it's not a guarantee. > > > Move this to before the first READ_ONCE(dev_priv->gt.active_requests); > > > so we stall before taking the lock, and skip if any new requests arrive > > > whilst waiting. > > > > > > (Also i915.enable_execlists is forbidden. But meh) > > > > > > static struct drm_i915_gem_request * > > > execlists_active_port(struct intel_engine_cs *engine) > > > { > > > struct drm_i915_gem_request *request; > > > > > > request = READ_ONCE(engine->execlist_port[1]); > > > if (request) > > > return request; > > > > > > return READ_ONCE(engine->execlist_port[0]); > > > } > > > > > > /* Wait for execlists to settle, but bail if any new requests come in */ > > > for_each_engine(engine, dev_priv, id) { > > > struct drm_i915_gem_request *request; > > > > > > request = execlists_active_port(engine); > > > if (!request) > > > continue; > > > > > > if (wait_for(execlists_active_port(engine) != request, 10)) > > > DRM_ERROR("Timeout waiting for %s to idle\n", engine->name); > > > } > > > > Hm, but we still need to re-check and bail out if not idle with > > struct_mutex held, since gt.active_requests could go 0->1->0 before > > taking struct_mutex? I can rewrite things with that check added, using > > the above. > > Hmm, apparently we don't care ;) If the context-done interrupt is > serialised with runtime suspend, then we don't need a wait here at all. > On the system path there are no new requests and we are just flushing > the idle worker. > > But yes, for the sake of correctness do both an unlocked wait followed > by a locked wait. Ok, will resend with this change. I used gt.active_requests to detect a new request during the unlocked wait, by that we can avoid polling in some cases. --Imre _______________________________________________ Intel-gfx mailing list Intel-gfx@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/intel-gfx
