Re: [Intel-gfx] [PATCH 20/46] drm/i915/guc: Add hang check to GuC submit engine

Matthew Brost
2021-08-09T19:06:03Z

On Mon, Aug 09, 2021 at 05:35:25PM +0200, Daniel Vetter wrote:
> On Tue, Aug 03, 2021 at 03:29:17PM -0700, Matthew Brost wrote:
> > The heartbeat uses a single instance of a GuC submit engine (GSE) to do
> > the hang check. As such if a different GSE's state machine hangs, the
> > heartbeat cannot detect this hang. Add timer to each GSE which in turn
> > can disable all submissions if it is hung.
> >
> > Cc: John Harrison <John.C.Harrison@Intel.com>
> > Signed-off-by: Matthew Brost <matthew.brost@intel.com>
> > ---
> > .../gpu/drm/i915/gt/uc/intel_guc_submission.c | 36 +++++++++++++++++++
> > .../i915/gt/uc/intel_guc_submission_types.h | 3 ++
> > 2 files changed, 39 insertions(+)
> >
> > diff --git a/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c b/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
> > index afb9b4bb8971..2d8296bcc583 100644
> > --- a/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
> > +++ b/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
> > @@ -105,15 +105,21 @@ static bool tasklet_blocked(struct guc_submit_engine *gse)
> > return test_bit(GSE_STATE_TASKLET_BLOCKED, &gse->flags);
> > }
> >
> > +/* 2 seconds seems like a reasonable timeout waiting for a G2H */
> > +#define MAX_TASKLET_BLOCKED_NS 2000000000
> > static void set_tasklet_blocked(struct guc_submit_engine *gse)
> > {
> > lockdep_assert_held(&gse->sched_engine.lock);
> > + hrtimer_start_range_ns(&gse->hang_timer,
> > + ns_to_ktime(MAX_TASKLET_BLOCKED_NS), 0,
> > + HRTIMER_MODE_REL_PINNED);
> > set_bit(GSE_STATE_TASKLET_BLOCKED, &gse->flags);
>
> So with drm/scheduler the reset handling is assumed to be
> single-threaded, and there's quite complex rules around that. I've
> recently worked with Boris Brezillion to clarify all this a bit and
> improve docs. Does this all still work in that glorious future? Might be
> good to at least sprinkle some comments/thoughts around in the commit
> message about the envisaged future direction for all this stuff, to keep
> people in the loop. Especially future people.
>
> Ofc plan is still to just largely land all this.
>
> Also: set_bit is an unordered atomic, which means you need barriers, which
> meanes ... *insert the full rant about justifying/documenting lockless
> algorithms from earlier *
>

lockdep_assert_held(&gse->sched_engine.lock);

Not lockless. Also spin locks act as barriers, right?

> But I think this all falls out with the removal of the guc-id allocation
> scheme?

Yes, this patch is getting deleted.

Matt

> -Daniel
>
> > }
> >
> > static void __clr_tasklet_blocked(struct guc_submit_engine *gse)
> > {
> > lockdep_assert_held(&gse->sched_engine.lock);
> > + hrtimer_cancel(&gse->hang_timer);
> > clear_bit(GSE_STATE_TASKLET_BLOCKED, &gse->flags);
> > }
> >
> > @@ -1028,6 +1034,7 @@ static void disable_submission(struct intel_guc *guc)
> > if (__tasklet_is_enabled(&sched_engine->tasklet)) {
> > GEM_BUG_ON(!guc->ct.enabled);
> > __tasklet_disable_sync_once(&sched_engine->tasklet);
> > + hrtimer_try_to_cancel(&guc->gse[i]->hang_timer);
> > sched_engine->tasklet.callback = NULL;
> > }
> > }
> > @@ -3750,6 +3757,33 @@ static void guc_sched_engine_destroy(struct kref *kref)
> > kfree(gse);
> > }
> >
> > +static enum hrtimer_restart gse_hang(struct hrtimer *hrtimer)
> > +{
> > + struct guc_submit_engine *gse =
> > + container_of(hrtimer, struct guc_submit_engine, hang_timer);
> > + struct intel_guc *guc = gse->sched_engine.private_data;
> > +
> > +#if IS_ENABLED(CONFIG_DRM_I915_SELFTEST)
> > + if (guc->gse_hang_expected)
> > + drm_dbg(&guc_to_gt(guc)->i915->drm,
> > + "GSE[%i] hung, disabling submission", gse->id);
> > + else
> > + drm_err(&guc_to_gt(guc)->i915->drm,
> > + "GSE[%i] hung, disabling submission", gse->id);
> > +#else
> > + drm_err(&guc_to_gt(guc)->i915->drm,
> > + "GSE[%i] hung, disabling submission", gse->id);
> > +#endif
> > +
> > + /*
> > + * Tasklet not making forward progress, disable submission which in turn
> > + * will kick in the heartbeat to do a full GPU reset.
> > + */
> > + disable_submission(guc);
> > +
> > + return HRTIMER_NORESTART;
> > +}
> > +
> > static void guc_submit_engine_init(struct intel_guc *guc,
> > struct guc_submit_engine *gse,
> > int id)
> > @@ -3767,6 +3801,8 @@ static void guc_submit_engine_init(struct intel_guc *guc,
> > sched_engine->retire_inflight_request_prio =
> > guc_retire_inflight_request_prio;
> > sched_engine->private_data = guc;
> > + hrtimer_init(&gse->hang_timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
> > + gse->hang_timer.function = gse_hang;
> > gse->id = id;
> > }
> >
> > diff --git a/drivers/gpu/drm/i915/gt/uc/intel_guc_submission_types.h b/drivers/gpu/drm/i915/gt/uc/intel_guc_submission_types.h
> > index a5933e07bdd2..eae2e9725ede 100644
> > --- a/drivers/gpu/drm/i915/gt/uc/intel_guc_submission_types.h
> > +++ b/drivers/gpu/drm/i915/gt/uc/intel_guc_submission_types.h
> > @@ -6,6 +6,8 @@
> > #ifndef _INTEL_GUC_SUBMISSION_TYPES_H_
> > #define _INTEL_GUC_SUBMISSION_TYPES_H_
> >
> > +#include <linux/xarray.h>
> > +
> > #include "gt/intel_engine_types.h"
> > #include "gt/intel_context_types.h"
> > #include "i915_scheduler_types.h"
> > @@ -41,6 +43,7 @@ struct guc_submit_engine {
> > unsigned long flags;
> > int total_num_rq_with_no_guc_id;
> > atomic_t num_guc_ids_not_ready;
> > + struct hrtimer hang_timer;
> > int id;
> >
> > /*
> > --
> > 2.28.0
> >
>
> --
> Daniel Vetter
> Software Engineer, Intel Corporation
> http://blog.ffwll.ch