Re: [PATCH] drm/i915/selftests: Try to show where the pulse went

[Mika Kuoppala <mika.kuoppala@linux.intel.com>]

Chris Wilson <chris@chris-wilson.co.uk> writes:

> We have a case of a mysteriously absent pulse, so dump the engine
> details to see if we can find out what happened to it.
>
> References: https://bugs.freedesktop.org/show_bug.cgi?id=112405
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> ---
>  drivers/gpu/drm/i915/gt/intel_engine_cs.c           | 2 ++
>  drivers/gpu/drm/i915/gt/selftest_engine_heartbeat.c | 5 +++++
>  2 files changed, 7 insertions(+)
>
> diff --git a/drivers/gpu/drm/i915/gt/intel_engine_cs.c b/drivers/gpu/drm/i915/gt/intel_engine_cs.c
> index 8f6e353caa66..df3369c3f330 100644
> --- a/drivers/gpu/drm/i915/gt/intel_engine_cs.c
> +++ b/drivers/gpu/drm/i915/gt/intel_engine_cs.c
> @@ -1479,6 +1479,8 @@ void intel_engine_dump(struct intel_engine_cs *engine,
>  		drm_printf(m, "*** WEDGED ***\n");
>  
>  	drm_printf(m, "\tAwake? %d\n", atomic_read(&engine->wakeref.count));
> +	drm_printf(m, "\tBarriers?: %s\n",
> +		   yesno(!llist_empty(&engine->barrier_tasks)));

A random thought arise when reading this and it was that
should we do a memory barrier before dump. But there
would be no pairing and it could actually hide something
more sinister.

It is important to know if and where and why did we drop
our stethoscope.

Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
>  
>  	rcu_read_lock();
>  	rq = READ_ONCE(engine->heartbeat.systole);
> diff --git a/drivers/gpu/drm/i915/gt/selftest_engine_heartbeat.c b/drivers/gpu/drm/i915/gt/selftest_engine_heartbeat.c
> index f665a0e23c61..0b1148cf3f61 100644
> --- a/drivers/gpu/drm/i915/gt/selftest_engine_heartbeat.c
> +++ b/drivers/gpu/drm/i915/gt/selftest_engine_heartbeat.c
> @@ -91,6 +91,11 @@ static int __live_idle_pulse(struct intel_engine_cs *engine,
>  	GEM_BUG_ON(!llist_empty(&engine->barrier_tasks));
>  
>  	if (intel_gt_retire_requests_timeout(engine->gt, HZ / 5)) {
> +		struct drm_printer m = drm_err_printer("pulse");
> +
> +		pr_err("%s: no heartbeat pulse?\n", engine->name);
> +		intel_engine_dump(engine, &m, "%s", engine->name);
> +
>  		err = -ETIME;
>  		goto out;
>  	}
> -- 
> 2.24.0
>
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