Chris Wilson <chris@xxxxxxxxxxxxxxxxxx> writes:
> Since commit 22b7a426bbe1 ("drm/i915/execlists: Preempt-to-busy"), we
> prune the engine->active.requests list prior to preemption, thus
> removing the trace of the currently executing request. If that request
> hangs rather than be preempted, we conclude that no active request was
> on the GPU. Fortunately, this only impacts our debugging, and not our
> means of hang detection or recovery.
>
> References: 22b7a426bbe1 ("drm/i915/execlists: Preempt-to-busy")
> Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
> Cc: Mika Kuoppala <mika.kuoppala@xxxxxxxxxxxxxxx>
> ---
> drivers/gpu/drm/i915/gt/intel_engine_cs.c | 29 ++++++++++++++++++-----
> 1 file changed, 23 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/gt/intel_engine_cs.c b/drivers/gpu/drm/i915/gt/intel_engine_cs.c
> index 06ff7695fa29..93878fd42a7a 100644
> --- a/drivers/gpu/drm/i915/gt/intel_engine_cs.c
> +++ b/drivers/gpu/drm/i915/gt/intel_engine_cs.c
> @@ -1643,7 +1643,7 @@ static bool match_ring(struct i915_request *rq)
> struct i915_request *
> intel_engine_find_active_request(struct intel_engine_cs *engine)
> {
> - struct i915_request *request, *active = NULL;
> + struct i915_request *rq, *active = NULL;
>
> /*
> * We are called by the error capture, reset and to dump engine
> @@ -1657,18 +1657,35 @@ intel_engine_find_active_request(struct intel_engine_cs *engine)
> * we only care about the snapshot of this moment.
> */
> lockdep_assert_held(&engine->active.lock);
> - list_for_each_entry(request, &engine->active.requests, sched.link) {
> - if (i915_request_completed(request))
> +
> + rcu_read_lock();
> + rq = execlists_active(&engine->execlists);
> + if (rq) {
> + struct intel_timeline *tl = rq->context->timeline;
> +
> + list_for_each_entry_continue_reverse(rq, &tl->requests, link) {
> + if (i915_request_completed(rq))
> + break;
This will be active - 1. So it makes me think that
we should first check that the real active has not completed.
-Mika
> +
> + active = rq;
> + }
> + }
> + rcu_read_unlock();
> + if (active)
> + return active;
> +
> + list_for_each_entry(rq, &engine->active.requests, sched.link) {
> + if (i915_request_completed(rq))
> continue;
>
> - if (!i915_request_started(request))
> + if (!i915_request_started(rq))
> continue;
>
> /* More than one preemptible request may match! */
> - if (!match_ring(request))
> + if (!match_ring(rq))
> continue;
>
> - active = request;
> + active = rq;
> break;
> }
>
> --
> 2.25.0
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