[Intel-gfx] [PATCH 02/28] drm/i915: Rename execlists->queue_priority to preempt_priority_hint
Tvrtko Ursulin
tvrtko.ursulin at linux.intel.com
Mon Jan 28 10:56:24 UTC 2019
On 28/01/2019 01:02, Chris Wilson wrote:
> After noticing that we trigger preemption events for currently executing
> requests, as well as requests that complete before the preemption and
> attempting to suppress those preemption events, it is wise to not
> consider the queue_priority to be authoritative. As we only track the
> maximum priority seen between dequeue passes, if the maximum priority
> request is no longer available for dequeuing (it completed or is even
> executing on another engine), we have no knowledge of the previous
> queue_priority as it would require us to keep a full history of enqueued
> requests -- but we already have that history in the priolists!
>
> Rename the queue_priority to preempt_priority_hint so that we do not
> confuse it as being the maximum priority in the queue, but merely an
> indication that we have seen a new maximum priority value and as such we
> should check whether it should preempt the currently running request.
>
> Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> Cc: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
> ---
> drivers/gpu/drm/i915/i915_scheduler.c | 11 +++++------
> drivers/gpu/drm/i915/intel_engine_cs.c | 4 ++--
> drivers/gpu/drm/i915/intel_guc_submission.c | 5 +++--
> drivers/gpu/drm/i915/intel_lrc.c | 20 +++++++++++---------
> drivers/gpu/drm/i915/intel_ringbuffer.h | 8 ++++++--
> 5 files changed, 27 insertions(+), 21 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/i915_scheduler.c b/drivers/gpu/drm/i915/i915_scheduler.c
> index 340faea6c08a..0da718ceab43 100644
> --- a/drivers/gpu/drm/i915/i915_scheduler.c
> +++ b/drivers/gpu/drm/i915/i915_scheduler.c
> @@ -127,8 +127,7 @@ static inline struct i915_priolist *to_priolist(struct rb_node *rb)
> return rb_entry(rb, struct i915_priolist, node);
> }
>
> -static void assert_priolists(struct intel_engine_execlists * const execlists,
> - long queue_priority)
> +static void assert_priolists(struct intel_engine_execlists * const execlists)
> {
> struct rb_node *rb;
> long last_prio, i;
> @@ -139,7 +138,7 @@ static void assert_priolists(struct intel_engine_execlists * const execlists,
> GEM_BUG_ON(rb_first_cached(&execlists->queue) !=
> rb_first(&execlists->queue.rb_root));
>
> - last_prio = (queue_priority >> I915_USER_PRIORITY_SHIFT) + 1;
> + last_prio = (INT_MAX >> I915_USER_PRIORITY_SHIFT) + 1;
> for (rb = rb_first_cached(&execlists->queue); rb; rb = rb_next(rb)) {
> const struct i915_priolist *p = to_priolist(rb);
>
> @@ -166,7 +165,7 @@ i915_sched_lookup_priolist(struct intel_engine_cs *engine, int prio)
> int idx, i;
>
> lockdep_assert_held(&engine->timeline.lock);
> - assert_priolists(execlists, INT_MAX);
> + assert_priolists(execlists);
>
> /* buckets sorted from highest [in slot 0] to lowest priority */
> idx = I915_PRIORITY_COUNT - (prio & I915_PRIORITY_MASK) - 1;
> @@ -353,7 +352,7 @@ static void __i915_schedule(struct i915_request *rq,
> continue;
> }
>
> - if (prio <= engine->execlists.queue_priority)
> + if (prio <= engine->execlists.preempt_priority_hint)
> continue;
>
> /*
> @@ -366,7 +365,7 @@ static void __i915_schedule(struct i915_request *rq,
> continue;
>
> /* Defer (tasklet) submission until after all of our updates. */
> - engine->execlists.queue_priority = prio;
> + engine->execlists.preempt_priority_hint = prio;
I am wondering whether stopping tracking the queue priority here, and
making it mean one thing only, would simplify things.
We make queue_priority strictly track the priority of whatever is in
port0 only, updated on dequeue and after context switch. Ie.
execlists.queue_priority gets the meaning of "top of the hw backend
queue priority".
For the purpose of kicking the tasklet that should work I think. It
wouldn't interrupt the port0 rq, and then on CS, dequeue would inspect
the real queue and see it there is need to preempt.
At the end of __i915_schedule we peek at top of the queue and decide
whether to kick the tasklet.
So we end up with two heads of queue priority. The HW backend one, and
the scheduling tree. Which seems like a clear separation of duties.
need_preempt() on dequeue then compares the two priorities only. Just
needs additional protection against not preempting the same context.
I hope I did not miss something, what do you think?
> tasklet_hi_schedule(&engine->execlists.tasklet);
> }
>
> diff --git a/drivers/gpu/drm/i915/intel_engine_cs.c b/drivers/gpu/drm/i915/intel_engine_cs.c
> index 1a5c163b98d6..1ffec0d69157 100644
> --- a/drivers/gpu/drm/i915/intel_engine_cs.c
> +++ b/drivers/gpu/drm/i915/intel_engine_cs.c
> @@ -480,7 +480,7 @@ static void intel_engine_init_execlist(struct intel_engine_cs *engine)
> GEM_BUG_ON(!is_power_of_2(execlists_num_ports(execlists)));
> GEM_BUG_ON(execlists_num_ports(execlists) > EXECLIST_MAX_PORTS);
>
> - execlists->queue_priority = INT_MIN;
> + execlists->preempt_priority_hint = INT_MIN;
> execlists->queue = RB_ROOT_CACHED;
> }
>
> @@ -1156,7 +1156,7 @@ void intel_engines_park(struct drm_i915_private *i915)
> }
>
> /* Must be reset upon idling, or we may miss the busy wakeup. */
> - GEM_BUG_ON(engine->execlists.queue_priority != INT_MIN);
> + GEM_BUG_ON(engine->execlists.preempt_priority_hint != INT_MIN);
>
> if (engine->park)
> engine->park(engine);
> diff --git a/drivers/gpu/drm/i915/intel_guc_submission.c b/drivers/gpu/drm/i915/intel_guc_submission.c
> index 45e2db683fe5..1bf6ac76ad99 100644
> --- a/drivers/gpu/drm/i915/intel_guc_submission.c
> +++ b/drivers/gpu/drm/i915/intel_guc_submission.c
> @@ -731,7 +731,7 @@ static bool __guc_dequeue(struct intel_engine_cs *engine)
> if (intel_engine_has_preemption(engine)) {
> struct guc_preempt_work *preempt_work =
> &engine->i915->guc.preempt_work[engine->id];
> - int prio = execlists->queue_priority;
> + int prio = execlists->preempt_priority_hint;
>
> if (__execlists_need_preempt(prio, port_prio(port))) {
> execlists_set_active(execlists,
> @@ -777,7 +777,8 @@ static bool __guc_dequeue(struct intel_engine_cs *engine)
> kmem_cache_free(engine->i915->priorities, p);
> }
> done:
> - execlists->queue_priority = rb ? to_priolist(rb)->priority : INT_MIN;
> + execlists->preempt_priority_hint =
> + rb ? to_priolist(rb)->priority : INT_MIN;
> if (submit)
> port_assign(port, last);
> if (last)
> diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
> index 185867106c14..71006b031f54 100644
> --- a/drivers/gpu/drm/i915/intel_lrc.c
> +++ b/drivers/gpu/drm/i915/intel_lrc.c
> @@ -584,7 +584,7 @@ static void execlists_dequeue(struct intel_engine_cs *engine)
> if (!execlists_is_active(execlists, EXECLISTS_ACTIVE_HWACK))
> return;
>
> - if (need_preempt(engine, last, execlists->queue_priority)) {
> + if (need_preempt(engine, last, execlists->preempt_priority_hint)) {
> inject_preempt_context(engine);
> return;
> }
> @@ -692,20 +692,20 @@ static void execlists_dequeue(struct intel_engine_cs *engine)
> /*
> * Here be a bit of magic! Or sleight-of-hand, whichever you prefer.
> *
> - * We choose queue_priority such that if we add a request of greater
> + * We choose the priority hint such that if we add a request of greater
> * priority than this, we kick the submission tasklet to decide on
> * the right order of submitting the requests to hardware. We must
> * also be prepared to reorder requests as they are in-flight on the
> - * HW. We derive the queue_priority then as the first "hole" in
> + * HW. We derive the priority hint then as the first "hole" in
> * the HW submission ports and if there are no available slots,
> * the priority of the lowest executing request, i.e. last.
> *
> * When we do receive a higher priority request ready to run from the
> - * user, see queue_request(), the queue_priority is bumped to that
> + * user, see queue_request(), the priority hint is bumped to that
> * request triggering preemption on the next dequeue (or subsequent
> * interrupt for secondary ports).
> */
> - execlists->queue_priority =
> + execlists->preempt_priority_hint =
> port != execlists->port ? rq_prio(last) : INT_MIN;
>
> if (submit) {
> @@ -853,7 +853,7 @@ static void execlists_cancel_requests(struct intel_engine_cs *engine)
>
> /* Remaining _unready_ requests will be nop'ed when submitted */
>
> - execlists->queue_priority = INT_MIN;
> + execlists->preempt_priority_hint = INT_MIN;
> execlists->queue = RB_ROOT_CACHED;
> GEM_BUG_ON(port_isset(execlists->port));
>
> @@ -1083,8 +1083,8 @@ static void __submit_queue_imm(struct intel_engine_cs *engine)
>
> static void submit_queue(struct intel_engine_cs *engine, int prio)
> {
> - if (prio > engine->execlists.queue_priority) {
> - engine->execlists.queue_priority = prio;
> + if (prio > engine->execlists.preempt_priority_hint) {
> + engine->execlists.preempt_priority_hint = prio;
> __submit_queue_imm(engine);
> }
> }
> @@ -2718,7 +2718,9 @@ void intel_execlists_show_requests(struct intel_engine_cs *engine,
>
> last = NULL;
> count = 0;
> - drm_printf(m, "\t\tQueue priority: %d\n", execlists->queue_priority);
> + if (execlists->preempt_priority_hint != INT_MIN)
> + drm_printf(m, "\t\tPreempt priority hint: %d\n",
> + execlists->preempt_priority_hint);
> for (rb = rb_first_cached(&execlists->queue); rb; rb = rb_next(rb)) {
> struct i915_priolist *p = rb_entry(rb, typeof(*p), node);
> int i;
> diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.h b/drivers/gpu/drm/i915/intel_ringbuffer.h
> index f2effd001540..71a41fec738f 100644
> --- a/drivers/gpu/drm/i915/intel_ringbuffer.h
> +++ b/drivers/gpu/drm/i915/intel_ringbuffer.h
> @@ -294,14 +294,18 @@ struct intel_engine_execlists {
> unsigned int port_mask;
>
> /**
> - * @queue_priority: Highest pending priority.
> + * @preempt_priority_hint: Highest pending priority.
> *
> * When we add requests into the queue, or adjust the priority of
> * executing requests, we compute the maximum priority of those
> * pending requests. We can then use this value to determine if
> * we need to preempt the executing requests to service the queue.
> + * However, since the we may have recorded the priority of an inflight
s/the/then/ or when? Not sure I still parse the sentence easily.
> + * request we wanted to preempt but since completed, at the time of
but has since completed? Which has?
> + * dequeuing the priority hint may no longer may match the highest
> + * available request priority.
> */
> - int queue_priority;
> + int preempt_priority_hint;
>
> /**
> * @queue: queue of requests, in priority lists
>
Regards,
Tvrtko
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