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

[Matthew Brost <matthew.brost@intel.com>]

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