| Message ID | 20210106123939.18435-4-chris@chris-wilson.co.uk (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [1/4] drm/i915/selftests: Break out of the lrc layout test after register mismatch | expand |
On 06/01/2021 12:39, Chris Wilson wrote: > In the next^W future patch, we remove the strict priority system and > continuously re-evaluate the relative priority of tasks. As such we need > to enable the timeslice whenever there is more than one context in the > pipeline. This simplifies the decision and removes some of the tweaks to > suppress timeslicing, allowing us to lift the timeslice enabling to a > common spot at the end of running the submission tasklet. > > One consequence of the suppression is that it was reducing fairness > between virtual engines on an over saturated system; undermining the > principle for timeslicing. > > Closes: https://gitlab.freedesktop.org/drm/intel/-/issues/2802 > Testcase: igt/gem_exec_balancer/fairslice > Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> > --- > drivers/gpu/drm/i915/gt/intel_engine_types.h | 10 - > .../drm/i915/gt/intel_execlists_submission.c | 173 +++++++----------- > 2 files changed, 68 insertions(+), 115 deletions(-) > > diff --git a/drivers/gpu/drm/i915/gt/intel_engine_types.h b/drivers/gpu/drm/i915/gt/intel_engine_types.h > index 430066e5884c..df62e793e747 100644 > --- a/drivers/gpu/drm/i915/gt/intel_engine_types.h > +++ b/drivers/gpu/drm/i915/gt/intel_engine_types.h > @@ -238,16 +238,6 @@ struct intel_engine_execlists { > */ > unsigned int port_mask; > > - /** > - * @switch_priority_hint: Second context priority. > - * > - * We submit multiple contexts to the HW simultaneously and would > - * like to occasionally switch between them to emulate timeslicing. > - * To know when timeslicing is suitable, we track the priority of > - * the context submitted second. > - */ > - int switch_priority_hint; > - > /** > * @queue_priority_hint: Highest pending priority. > * > diff --git a/drivers/gpu/drm/i915/gt/intel_execlists_submission.c b/drivers/gpu/drm/i915/gt/intel_execlists_submission.c > index ba3114fd4389..50d4308023f3 100644 > --- a/drivers/gpu/drm/i915/gt/intel_execlists_submission.c > +++ b/drivers/gpu/drm/i915/gt/intel_execlists_submission.c > @@ -1143,25 +1143,6 @@ static void defer_active(struct intel_engine_cs *engine) > defer_request(rq, i915_sched_lookup_priolist(engine, rq_prio(rq))); > } > > -static bool > -need_timeslice(const struct intel_engine_cs *engine, > - const struct i915_request *rq) > -{ > - int hint; > - > - if (!intel_engine_has_timeslices(engine)) > - return false; > - > - hint = max(engine->execlists.queue_priority_hint, > - virtual_prio(&engine->execlists)); > - > - if (!list_is_last(&rq->sched.link, &engine->active.requests)) > - hint = max(hint, rq_prio(list_next_entry(rq, sched.link))); > - > - GEM_BUG_ON(hint >= I915_PRIORITY_UNPREEMPTABLE); > - return hint >= effective_prio(rq); > -} > - > static bool > timeslice_yield(const struct intel_engine_execlists *el, > const struct i915_request *rq) > @@ -1181,76 +1162,68 @@ timeslice_yield(const struct intel_engine_execlists *el, > return rq->context->lrc.ccid == READ_ONCE(el->yield); > } > > -static bool > -timeslice_expired(const struct intel_engine_execlists *el, > - const struct i915_request *rq) > +static bool needs_timeslice(const struct intel_engine_cs *engine, > + const struct i915_request *rq) > { > + if (!intel_engine_has_timeslices(engine)) > + return false; > + > + /* If not currently active, or about to switch, wait for next event */ > + if (!rq || __i915_request_is_complete(rq)) > + return false; > + > + /* We do not need to start the timeslice until after the ACK */ > + if (READ_ONCE(engine->execlists.pending[0])) > + return false; > + > + /* If ELSP[1] is occupied, always check to see if worth slicing */ > + if (!list_is_last_rcu(&rq->sched.link, &engine->active.requests)) > + return true; > + > + /* Otherwise, ELSP[0] is by itself, but may be waiting in the queue */ > + if (!RB_EMPTY_ROOT(&engine->execlists.queue.rb_root)) > + return true; > + > + return !RB_EMPTY_ROOT(&engine->execlists.virtual.rb_root); > +} > + > +static bool > +timeslice_expired(struct intel_engine_cs *engine, const struct i915_request *rq) > +{ > + const struct intel_engine_execlists *el = &engine->execlists; > + > + if (i915_request_has_nopreempt(rq) && __i915_request_has_started(rq)) > + return false; > + > + if (!needs_timeslice(engine, rq)) > + return false; > + > return timer_expired(&el->timer) || timeslice_yield(el, rq); > } > > -static int > -switch_prio(struct intel_engine_cs *engine, const struct i915_request *rq) > -{ > - if (list_is_last(&rq->sched.link, &engine->active.requests)) > - return engine->execlists.queue_priority_hint; > - > - return rq_prio(list_next_entry(rq, sched.link)); > -} > - > -static inline unsigned long > -timeslice(const struct intel_engine_cs *engine) > +static unsigned long timeslice(const struct intel_engine_cs *engine) > { > return READ_ONCE(engine->props.timeslice_duration_ms); > } > > -static unsigned long active_timeslice(const struct intel_engine_cs *engine) > -{ > - const struct intel_engine_execlists *execlists = &engine->execlists; > - const struct i915_request *rq = *execlists->active; > - > - if (!rq || __i915_request_is_complete(rq)) > - return 0; > - > - if (READ_ONCE(execlists->switch_priority_hint) < effective_prio(rq)) > - return 0; > - > - return timeslice(engine); > -} > - > -static void set_timeslice(struct intel_engine_cs *engine) > +static void start_timeslice(struct intel_engine_cs *engine) > { > + struct intel_engine_execlists *el = &engine->execlists; > unsigned long duration; > > - if (!intel_engine_has_timeslices(engine)) > - return; > + /* Disable the timer if there is nothing to switch to */ > + duration = 0; > + if (needs_timeslice(engine, *el->active)) { > + if (el->timer.expires) { Why not just timer_pending check? Are you sure timer->expires cannot legitimately be at jiffie 0 in wrap conditions? > + if (!timer_pending(&el->timer)) > + tasklet_hi_schedule(&engine->execlists.tasklet); > + return; > + } > > - duration = active_timeslice(engine); > - ENGINE_TRACE(engine, "bump timeslicing, interval:%lu", duration); > + duration = timeslice(engine); > + } > > - set_timer_ms(&engine->execlists.timer, duration); > -} > - > -static void start_timeslice(struct intel_engine_cs *engine, int prio) > -{ > - struct intel_engine_execlists *execlists = &engine->execlists; > - unsigned long duration; > - > - if (!intel_engine_has_timeslices(engine)) > - return; > - > - WRITE_ONCE(execlists->switch_priority_hint, prio); > - if (prio == INT_MIN) > - return; > - > - if (timer_pending(&execlists->timer)) > - return; > - > - duration = timeslice(engine); > - ENGINE_TRACE(engine, > - "start timeslicing, prio:%d, interval:%lu", > - prio, duration); > - > - set_timer_ms(&execlists->timer, duration); > + set_timer_ms(&el->timer, duration); > } > > static void record_preemption(struct intel_engine_execlists *execlists) > @@ -1363,16 +1336,16 @@ static void execlists_dequeue(struct intel_engine_cs *engine) > __unwind_incomplete_requests(engine); > > last = NULL; > - } else if (need_timeslice(engine, last) && > - timeslice_expired(execlists, last)) { > + } else if (timeslice_expired(engine, last)) { > ENGINE_TRACE(engine, > - "expired last=%llx:%lld, prio=%d, hint=%d, yield?=%s\n", > - last->fence.context, > - last->fence.seqno, > - last->sched.attr.priority, > + "expired:%s last=%llx:%lld, prio=%d, hint=%d, yield?=%s\n", > + yesno(timer_expired(&execlists->timer)), > + last->fence.context, last->fence.seqno, > + rq_prio(last), > execlists->queue_priority_hint, > yesno(timeslice_yield(execlists, last))); > > + cancel_timer(&execlists->timer); What is this cancel for? Regards, Tvrtko > ring_set_paused(engine, 1); > defer_active(engine); > > @@ -1408,7 +1381,6 @@ static void execlists_dequeue(struct intel_engine_cs *engine) > * of timeslices, our queue might be. > */ > spin_unlock(&engine->active.lock); > - start_timeslice(engine, queue_prio(execlists)); > return; > } > } > @@ -1435,7 +1407,6 @@ static void execlists_dequeue(struct intel_engine_cs *engine) > if (last && !can_merge_rq(last, rq)) { > spin_unlock(&ve->base.active.lock); > spin_unlock(&engine->active.lock); > - start_timeslice(engine, rq_prio(rq)); > return; /* leave this for another sibling */ > } > > @@ -1599,29 +1570,23 @@ static void execlists_dequeue(struct intel_engine_cs *engine) > execlists->queue_priority_hint = queue_prio(execlists); > spin_unlock(&engine->active.lock); > > - if (submit) { > - /* > - * Skip if we ended up with exactly the same set of requests, > - * e.g. trying to timeslice a pair of ordered contexts > - */ > - if (!memcmp(execlists->active, > - execlists->pending, > - (port - execlists->pending) * sizeof(*port))) > - goto skip_submit; > - > + /* > + * We can skip poking the HW if we ended up with exactly the same set > + * of requests as currently running, e.g. trying to timeslice a pair > + * of ordered contexts. > + */ > + if (submit && > + memcmp(execlists->active, > + execlists->pending, > + (port - execlists->pending) * sizeof(*port))) { > *port = NULL; > while (port-- != execlists->pending) > execlists_schedule_in(*port, port - execlists->pending); > > - execlists->switch_priority_hint = > - switch_prio(engine, *execlists->pending); > - > WRITE_ONCE(execlists->yield, -1); > set_preempt_timeout(engine, *execlists->active); > execlists_submit_ports(engine); > } else { > - start_timeslice(engine, execlists->queue_priority_hint); > -skip_submit: > ring_set_paused(engine, 0); > while (port-- != execlists->pending) > i915_request_put(*port); > @@ -1979,8 +1944,6 @@ process_csb(struct intel_engine_cs *engine, struct i915_request **inactive) > } > } while (head != tail); > > - set_timeslice(engine); > - > /* > * Gen11 has proven to fail wrt global observation point between > * entry and tail update, failing on the ordering and thus > @@ -1993,6 +1956,7 @@ process_csb(struct intel_engine_cs *engine, struct i915_request **inactive) > * invalidation before. > */ > invalidate_csb_entries(&buf[0], &buf[num_entries - 1]); > + cancel_timer(&execlists->timer); > > return inactive; > } > @@ -2405,8 +2369,10 @@ static void execlists_submission_tasklet(unsigned long data) > execlists_reset(engine, msg); > } > > - if (!engine->execlists.pending[0]) > + if (!engine->execlists.pending[0]) { > execlists_dequeue_irq(engine); > + start_timeslice(engine); > + } > > post_process_csb(post, inactive); > rcu_read_unlock(); > @@ -3851,9 +3817,6 @@ void intel_execlists_show_requests(struct intel_engine_cs *engine, > show_request(m, last, "\t\t", 0); > } > > - if (execlists->switch_priority_hint != INT_MIN) > - drm_printf(m, "\t\tSwitch priority hint: %d\n", > - READ_ONCE(execlists->switch_priority_hint)); > if (execlists->queue_priority_hint != INT_MIN) > drm_printf(m, "\t\tQueue priority hint: %d\n", > READ_ONCE(execlists->queue_priority_hint)); >
Quoting Tvrtko Ursulin (2021-01-06 15:57:49) > > > On 06/01/2021 12:39, Chris Wilson wrote: > > In the next^W future patch, we remove the strict priority system and > > continuously re-evaluate the relative priority of tasks. As such we need > > to enable the timeslice whenever there is more than one context in the > > pipeline. This simplifies the decision and removes some of the tweaks to > > suppress timeslicing, allowing us to lift the timeslice enabling to a > > common spot at the end of running the submission tasklet. > > > > One consequence of the suppression is that it was reducing fairness > > between virtual engines on an over saturated system; undermining the > > principle for timeslicing. > > > > Closes: https://gitlab.freedesktop.org/drm/intel/-/issues/2802 > > Testcase: igt/gem_exec_balancer/fairslice > > Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> > > --- > > drivers/gpu/drm/i915/gt/intel_engine_types.h | 10 - > > .../drm/i915/gt/intel_execlists_submission.c | 173 +++++++----------- > > 2 files changed, 68 insertions(+), 115 deletions(-) > > > > diff --git a/drivers/gpu/drm/i915/gt/intel_engine_types.h b/drivers/gpu/drm/i915/gt/intel_engine_types.h > > index 430066e5884c..df62e793e747 100644 > > --- a/drivers/gpu/drm/i915/gt/intel_engine_types.h > > +++ b/drivers/gpu/drm/i915/gt/intel_engine_types.h > > @@ -238,16 +238,6 @@ struct intel_engine_execlists { > > */ > > unsigned int port_mask; > > > > - /** > > - * @switch_priority_hint: Second context priority. > > - * > > - * We submit multiple contexts to the HW simultaneously and would > > - * like to occasionally switch between them to emulate timeslicing. > > - * To know when timeslicing is suitable, we track the priority of > > - * the context submitted second. > > - */ > > - int switch_priority_hint; > > - > > /** > > * @queue_priority_hint: Highest pending priority. > > * > > diff --git a/drivers/gpu/drm/i915/gt/intel_execlists_submission.c b/drivers/gpu/drm/i915/gt/intel_execlists_submission.c > > index ba3114fd4389..50d4308023f3 100644 > > --- a/drivers/gpu/drm/i915/gt/intel_execlists_submission.c > > +++ b/drivers/gpu/drm/i915/gt/intel_execlists_submission.c > > @@ -1143,25 +1143,6 @@ static void defer_active(struct intel_engine_cs *engine) > > defer_request(rq, i915_sched_lookup_priolist(engine, rq_prio(rq))); > > } > > > > -static bool > > -need_timeslice(const struct intel_engine_cs *engine, > > - const struct i915_request *rq) > > -{ > > - int hint; > > - > > - if (!intel_engine_has_timeslices(engine)) > > - return false; > > - > > - hint = max(engine->execlists.queue_priority_hint, > > - virtual_prio(&engine->execlists)); > > - > > - if (!list_is_last(&rq->sched.link, &engine->active.requests)) > > - hint = max(hint, rq_prio(list_next_entry(rq, sched.link))); > > - > > - GEM_BUG_ON(hint >= I915_PRIORITY_UNPREEMPTABLE); > > - return hint >= effective_prio(rq); > > -} > > - > > static bool > > timeslice_yield(const struct intel_engine_execlists *el, > > const struct i915_request *rq) > > @@ -1181,76 +1162,68 @@ timeslice_yield(const struct intel_engine_execlists *el, > > return rq->context->lrc.ccid == READ_ONCE(el->yield); > > } > > > > -static bool > > -timeslice_expired(const struct intel_engine_execlists *el, > > - const struct i915_request *rq) > > +static bool needs_timeslice(const struct intel_engine_cs *engine, > > + const struct i915_request *rq) > > { > > + if (!intel_engine_has_timeslices(engine)) > > + return false; > > + > > + /* If not currently active, or about to switch, wait for next event */ > > + if (!rq || __i915_request_is_complete(rq)) > > + return false; > > + > > + /* We do not need to start the timeslice until after the ACK */ > > + if (READ_ONCE(engine->execlists.pending[0])) > > + return false; > > + > > + /* If ELSP[1] is occupied, always check to see if worth slicing */ > > + if (!list_is_last_rcu(&rq->sched.link, &engine->active.requests)) > > + return true; > > + > > + /* Otherwise, ELSP[0] is by itself, but may be waiting in the queue */ > > + if (!RB_EMPTY_ROOT(&engine->execlists.queue.rb_root)) > > + return true; > > + > > + return !RB_EMPTY_ROOT(&engine->execlists.virtual.rb_root); > > +} > > + > > +static bool > > +timeslice_expired(struct intel_engine_cs *engine, const struct i915_request *rq) > > +{ > > + const struct intel_engine_execlists *el = &engine->execlists; > > + > > + if (i915_request_has_nopreempt(rq) && __i915_request_has_started(rq)) > > + return false; > > + > > + if (!needs_timeslice(engine, rq)) > > + return false; > > + > > return timer_expired(&el->timer) || timeslice_yield(el, rq); > > } > > > > -static int > > -switch_prio(struct intel_engine_cs *engine, const struct i915_request *rq) > > -{ > > - if (list_is_last(&rq->sched.link, &engine->active.requests)) > > - return engine->execlists.queue_priority_hint; > > - > > - return rq_prio(list_next_entry(rq, sched.link)); > > -} > > - > > -static inline unsigned long > > -timeslice(const struct intel_engine_cs *engine) > > +static unsigned long timeslice(const struct intel_engine_cs *engine) > > { > > return READ_ONCE(engine->props.timeslice_duration_ms); > > } > > > > -static unsigned long active_timeslice(const struct intel_engine_cs *engine) > > -{ > > - const struct intel_engine_execlists *execlists = &engine->execlists; > > - const struct i915_request *rq = *execlists->active; > > - > > - if (!rq || __i915_request_is_complete(rq)) > > - return 0; > > - > > - if (READ_ONCE(execlists->switch_priority_hint) < effective_prio(rq)) > > - return 0; > > - > > - return timeslice(engine); > > -} > > - > > -static void set_timeslice(struct intel_engine_cs *engine) > > +static void start_timeslice(struct intel_engine_cs *engine) > > { > > + struct intel_engine_execlists *el = &engine->execlists; > > unsigned long duration; > > > > - if (!intel_engine_has_timeslices(engine)) > > - return; > > + /* Disable the timer if there is nothing to switch to */ > > + duration = 0; > > + if (needs_timeslice(engine, *el->active)) { > > + if (el->timer.expires) { > > Why not just timer_pending check? Are you sure timer->expires cannot > legitimately be at jiffie 0 in wrap conditions? This is actually to test if we have set the timer or not, and avoid extending an already active timeslice. We are abusing the jiffie wrap being unlikely and of no great consequence (one missed timeslice/preempt timer should be picked up by the next poke of the driver) as part of set_timer_ms/cancel_timer. > > + if (!timer_pending(&el->timer)) > > + tasklet_hi_schedule(&engine->execlists.tasklet); > > + return; > > + } > > > > - duration = active_timeslice(engine); > > - ENGINE_TRACE(engine, "bump timeslicing, interval:%lu", duration); > > + duration = timeslice(engine); > > + } > > > > - set_timer_ms(&engine->execlists.timer, duration); > > -} > > - > > -static void start_timeslice(struct intel_engine_cs *engine, int prio) > > -{ > > - struct intel_engine_execlists *execlists = &engine->execlists; > > - unsigned long duration; > > - > > - if (!intel_engine_has_timeslices(engine)) > > - return; > > - > > - WRITE_ONCE(execlists->switch_priority_hint, prio); > > - if (prio == INT_MIN) > > - return; > > - > > - if (timer_pending(&execlists->timer)) > > - return; > > - > > - duration = timeslice(engine); > > - ENGINE_TRACE(engine, > > - "start timeslicing, prio:%d, interval:%lu", > > - prio, duration); > > - > > - set_timer_ms(&execlists->timer, duration); > > + set_timer_ms(&el->timer, duration); > > } > > > > static void record_preemption(struct intel_engine_execlists *execlists) > > @@ -1363,16 +1336,16 @@ static void execlists_dequeue(struct intel_engine_cs *engine) > > __unwind_incomplete_requests(engine); > > > > last = NULL; > > - } else if (need_timeslice(engine, last) && > > - timeslice_expired(execlists, last)) { > > + } else if (timeslice_expired(engine, last)) { > > ENGINE_TRACE(engine, > > - "expired last=%llx:%lld, prio=%d, hint=%d, yield?=%s\n", > > - last->fence.context, > > - last->fence.seqno, > > - last->sched.attr.priority, > > + "expired:%s last=%llx:%lld, prio=%d, hint=%d, yield?=%s\n", > > + yesno(timer_expired(&execlists->timer)), > > + last->fence.context, last->fence.seqno, > > + rq_prio(last), > > execlists->queue_priority_hint, > > yesno(timeslice_yield(execlists, last))); > > > > + cancel_timer(&execlists->timer); > > What is this cancel for? This branch is taken upon yielding the timeslice, but we may not submit a new pair of contexts, leaving the timer active (and marked as expired). Since the timer remains expired, we will continuously looped until a context switch, or some other preemption event. -Chris
Quoting Chris Wilson (2021-01-06 16:08:40) > Quoting Tvrtko Ursulin (2021-01-06 15:57:49) > > > > > > On 06/01/2021 12:39, Chris Wilson wrote: > > > In the next^W future patch, we remove the strict priority system and > > > continuously re-evaluate the relative priority of tasks. As such we need > > > to enable the timeslice whenever there is more than one context in the > > > pipeline. This simplifies the decision and removes some of the tweaks to > > > suppress timeslicing, allowing us to lift the timeslice enabling to a > > > common spot at the end of running the submission tasklet. > > > > > > One consequence of the suppression is that it was reducing fairness > > > between virtual engines on an over saturated system; undermining the > > > principle for timeslicing. > > > > > > Closes: https://gitlab.freedesktop.org/drm/intel/-/issues/2802 > > > Testcase: igt/gem_exec_balancer/fairslice > > > Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> > > > --- > > > drivers/gpu/drm/i915/gt/intel_engine_types.h | 10 - > > > .../drm/i915/gt/intel_execlists_submission.c | 173 +++++++----------- > > > 2 files changed, 68 insertions(+), 115 deletions(-) > > > > > > diff --git a/drivers/gpu/drm/i915/gt/intel_engine_types.h b/drivers/gpu/drm/i915/gt/intel_engine_types.h > > > index 430066e5884c..df62e793e747 100644 > > > --- a/drivers/gpu/drm/i915/gt/intel_engine_types.h > > > +++ b/drivers/gpu/drm/i915/gt/intel_engine_types.h > > > @@ -238,16 +238,6 @@ struct intel_engine_execlists { > > > */ > > > unsigned int port_mask; > > > > > > - /** > > > - * @switch_priority_hint: Second context priority. > > > - * > > > - * We submit multiple contexts to the HW simultaneously and would > > > - * like to occasionally switch between them to emulate timeslicing. > > > - * To know when timeslicing is suitable, we track the priority of > > > - * the context submitted second. > > > - */ > > > - int switch_priority_hint; > > > - > > > /** > > > * @queue_priority_hint: Highest pending priority. > > > * > > > diff --git a/drivers/gpu/drm/i915/gt/intel_execlists_submission.c b/drivers/gpu/drm/i915/gt/intel_execlists_submission.c > > > index ba3114fd4389..50d4308023f3 100644 > > > --- a/drivers/gpu/drm/i915/gt/intel_execlists_submission.c > > > +++ b/drivers/gpu/drm/i915/gt/intel_execlists_submission.c > > > @@ -1143,25 +1143,6 @@ static void defer_active(struct intel_engine_cs *engine) > > > defer_request(rq, i915_sched_lookup_priolist(engine, rq_prio(rq))); > > > } > > > > > > -static bool > > > -need_timeslice(const struct intel_engine_cs *engine, > > > - const struct i915_request *rq) > > > -{ > > > - int hint; > > > - > > > - if (!intel_engine_has_timeslices(engine)) > > > - return false; > > > - > > > - hint = max(engine->execlists.queue_priority_hint, > > > - virtual_prio(&engine->execlists)); > > > - > > > - if (!list_is_last(&rq->sched.link, &engine->active.requests)) > > > - hint = max(hint, rq_prio(list_next_entry(rq, sched.link))); > > > - > > > - GEM_BUG_ON(hint >= I915_PRIORITY_UNPREEMPTABLE); > > > - return hint >= effective_prio(rq); > > > -} > > > - > > > static bool > > > timeslice_yield(const struct intel_engine_execlists *el, > > > const struct i915_request *rq) > > > @@ -1181,76 +1162,68 @@ timeslice_yield(const struct intel_engine_execlists *el, > > > return rq->context->lrc.ccid == READ_ONCE(el->yield); > > > } > > > > > > -static bool > > > -timeslice_expired(const struct intel_engine_execlists *el, > > > - const struct i915_request *rq) > > > +static bool needs_timeslice(const struct intel_engine_cs *engine, > > > + const struct i915_request *rq) > > > { > > > + if (!intel_engine_has_timeslices(engine)) > > > + return false; > > > + > > > + /* If not currently active, or about to switch, wait for next event */ > > > + if (!rq || __i915_request_is_complete(rq)) > > > + return false; > > > + > > > + /* We do not need to start the timeslice until after the ACK */ > > > + if (READ_ONCE(engine->execlists.pending[0])) > > > + return false; > > > + > > > + /* If ELSP[1] is occupied, always check to see if worth slicing */ > > > + if (!list_is_last_rcu(&rq->sched.link, &engine->active.requests)) > > > + return true; > > > + > > > + /* Otherwise, ELSP[0] is by itself, but may be waiting in the queue */ > > > + if (!RB_EMPTY_ROOT(&engine->execlists.queue.rb_root)) > > > + return true; > > > + > > > + return !RB_EMPTY_ROOT(&engine->execlists.virtual.rb_root); > > > +} > > > + > > > +static bool > > > +timeslice_expired(struct intel_engine_cs *engine, const struct i915_request *rq) > > > +{ > > > + const struct intel_engine_execlists *el = &engine->execlists; > > > + > > > + if (i915_request_has_nopreempt(rq) && __i915_request_has_started(rq)) > > > + return false; > > > + > > > + if (!needs_timeslice(engine, rq)) > > > + return false; > > > + > > > return timer_expired(&el->timer) || timeslice_yield(el, rq); > > > } > > > > > > -static int > > > -switch_prio(struct intel_engine_cs *engine, const struct i915_request *rq) > > > -{ > > > - if (list_is_last(&rq->sched.link, &engine->active.requests)) > > > - return engine->execlists.queue_priority_hint; > > > - > > > - return rq_prio(list_next_entry(rq, sched.link)); > > > -} > > > - > > > -static inline unsigned long > > > -timeslice(const struct intel_engine_cs *engine) > > > +static unsigned long timeslice(const struct intel_engine_cs *engine) > > > { > > > return READ_ONCE(engine->props.timeslice_duration_ms); > > > } > > > > > > -static unsigned long active_timeslice(const struct intel_engine_cs *engine) > > > -{ > > > - const struct intel_engine_execlists *execlists = &engine->execlists; > > > - const struct i915_request *rq = *execlists->active; > > > - > > > - if (!rq || __i915_request_is_complete(rq)) > > > - return 0; > > > - > > > - if (READ_ONCE(execlists->switch_priority_hint) < effective_prio(rq)) > > > - return 0; > > > - > > > - return timeslice(engine); > > > -} > > > - > > > -static void set_timeslice(struct intel_engine_cs *engine) > > > +static void start_timeslice(struct intel_engine_cs *engine) > > > { > > > + struct intel_engine_execlists *el = &engine->execlists; > > > unsigned long duration; > > > > > > - if (!intel_engine_has_timeslices(engine)) > > > - return; > > > + /* Disable the timer if there is nothing to switch to */ > > > + duration = 0; > > > + if (needs_timeslice(engine, *el->active)) { > > > + if (el->timer.expires) { > > > > Why not just timer_pending check? Are you sure timer->expires cannot > > legitimately be at jiffie 0 in wrap conditions? > > This is actually to test if we have set the timer or not, and avoid > extending an already active timeslice. We are abusing the jiffie wrap > being unlikely and of no great consequence (one missed timeslice/preempt > timer should be picked up by the next poke of the driver) as part of > set_timer_ms/cancel_timer. I see you've asked this before: void set_timer_ms(struct timer_list *t, unsigned long timeout) { if (!timeout) { cancel_timer(t); return; } timeout = msecs_to_jiffies(timeout); /* * Paranoia to make sure the compiler computes the timeout before * loading 'jiffies' as jiffies is volatile and may be updated in * the background by a timer tick. All to reduce the complexity * of the addition and reduce the risk of losing a jiffie. */ barrier(); /* Keep t->expires = 0 reserved to indicate a canceled timer. */ mod_timer(t, jiffies + timeout ?: 1); } :) -Chris
On 06/01/2021 16:08, Chris Wilson wrote: > Quoting Tvrtko Ursulin (2021-01-06 15:57:49) [snip] >>> @@ -1363,16 +1336,16 @@ static void execlists_dequeue(struct intel_engine_cs *engine) >>> __unwind_incomplete_requests(engine); >>> >>> last = NULL; >>> - } else if (need_timeslice(engine, last) && >>> - timeslice_expired(execlists, last)) { >>> + } else if (timeslice_expired(engine, last)) { >>> ENGINE_TRACE(engine, >>> - "expired last=%llx:%lld, prio=%d, hint=%d, yield?=%s\n", >>> - last->fence.context, >>> - last->fence.seqno, >>> - last->sched.attr.priority, >>> + "expired:%s last=%llx:%lld, prio=%d, hint=%d, yield?=%s\n", >>> + yesno(timer_expired(&execlists->timer)), >>> + last->fence.context, last->fence.seqno, >>> + rq_prio(last), >>> execlists->queue_priority_hint, >>> yesno(timeslice_yield(execlists, last))); >>> >>> + cancel_timer(&execlists->timer); >> >> What is this cancel for? > > This branch is taken upon yielding the timeslice, but we may not submit > a new pair of contexts, leaving the timer active (and marked as > expired). Since the timer remains expired, we will continuously looped > until a context switch, or some other preemption event. Sorry I was looking at the cancel_timer in process_csb and ended up replying at the wrong spot. The situation there seems to be removing the single timeslice related call (set_timeslice) and adding a cancel_timer which is also not obvious to me what it is about. Regards, Tvrtko
Quoting Tvrtko Ursulin (2021-01-07 10:16:57) > > On 06/01/2021 16:08, Chris Wilson wrote: > > Quoting Tvrtko Ursulin (2021-01-06 15:57:49) > > [snip] > > >>> @@ -1363,16 +1336,16 @@ static void execlists_dequeue(struct intel_engine_cs *engine) > >>> __unwind_incomplete_requests(engine); > >>> > >>> last = NULL; > >>> - } else if (need_timeslice(engine, last) && > >>> - timeslice_expired(execlists, last)) { > >>> + } else if (timeslice_expired(engine, last)) { > >>> ENGINE_TRACE(engine, > >>> - "expired last=%llx:%lld, prio=%d, hint=%d, yield?=%s\n", > >>> - last->fence.context, > >>> - last->fence.seqno, > >>> - last->sched.attr.priority, > >>> + "expired:%s last=%llx:%lld, prio=%d, hint=%d, yield?=%s\n", > >>> + yesno(timer_expired(&execlists->timer)), > >>> + last->fence.context, last->fence.seqno, > >>> + rq_prio(last), > >>> execlists->queue_priority_hint, > >>> yesno(timeslice_yield(execlists, last))); > >>> > >>> + cancel_timer(&execlists->timer); > >> > >> What is this cancel for? > > > > This branch is taken upon yielding the timeslice, but we may not submit > > a new pair of contexts, leaving the timer active (and marked as > > expired). Since the timer remains expired, we will continuously looped > > until a context switch, or some other preemption event. > > Sorry I was looking at the cancel_timer in process_csb and ended up > replying at the wrong spot. The situation there seems to be removing the > single timeslice related call (set_timeslice) and adding a cancel_timer > which is also not obvious to me what it is about. Yes, there the cancel_timer() is equivalent to the old set_timeslice(). After processing an event, we assume it is a change in context meriting a new timeslice. To start a new timeslice rather than continue the old one, we remove an existing timer and readd it for the end of the timeslice. -Chris
On 07/01/2021 10:27, Chris Wilson wrote: > Quoting Tvrtko Ursulin (2021-01-07 10:16:57) >> >> On 06/01/2021 16:08, Chris Wilson wrote: >>> Quoting Tvrtko Ursulin (2021-01-06 15:57:49) >> >> [snip] >> >>>>> @@ -1363,16 +1336,16 @@ static void execlists_dequeue(struct intel_engine_cs *engine) >>>>> __unwind_incomplete_requests(engine); >>>>> >>>>> last = NULL; >>>>> - } else if (need_timeslice(engine, last) && >>>>> - timeslice_expired(execlists, last)) { >>>>> + } else if (timeslice_expired(engine, last)) { >>>>> ENGINE_TRACE(engine, >>>>> - "expired last=%llx:%lld, prio=%d, hint=%d, yield?=%s\n", >>>>> - last->fence.context, >>>>> - last->fence.seqno, >>>>> - last->sched.attr.priority, >>>>> + "expired:%s last=%llx:%lld, prio=%d, hint=%d, yield?=%s\n", >>>>> + yesno(timer_expired(&execlists->timer)), >>>>> + last->fence.context, last->fence.seqno, >>>>> + rq_prio(last), >>>>> execlists->queue_priority_hint, >>>>> yesno(timeslice_yield(execlists, last))); >>>>> >>>>> + cancel_timer(&execlists->timer); >>>> >>>> What is this cancel for? >>> >>> This branch is taken upon yielding the timeslice, but we may not submit >>> a new pair of contexts, leaving the timer active (and marked as >>> expired). Since the timer remains expired, we will continuously looped >>> until a context switch, or some other preemption event. >> >> Sorry I was looking at the cancel_timer in process_csb and ended up >> replying at the wrong spot. The situation there seems to be removing the >> single timeslice related call (set_timeslice) and adding a cancel_timer >> which is also not obvious to me what it is about. > > Yes, there the cancel_timer() is equivalent to the old set_timeslice(). > > After processing an event, we assume it is a change in context meriting > a new timeslice. To start a new timeslice rather than continue the old > one, we remove an existing timer and readd it for the end of the > timeslice. I was looking what is the resulting symmetry of start/cancel call sites. We end up with a single start_timeslice call from the tasklet, but guarded with !pending. That looked confusing at first until I remembered you mentioned (or a comment somewhere already says) that the idea is to only start the timeslice after the csb ack. That explains the transition from timer disabled to timer enabled. Then as long as there are contexts queued code relies on timeslice expiry, or re-submission with change, to temporarily suspend the timer. It looks okay as far as I can see. Will tag the latest. Regards, Tvrtko
diff --git a/drivers/gpu/drm/i915/gt/intel_engine_types.h b/drivers/gpu/drm/i915/gt/intel_engine_types.h index 430066e5884c..df62e793e747 100644 --- a/drivers/gpu/drm/i915/gt/intel_engine_types.h +++ b/drivers/gpu/drm/i915/gt/intel_engine_types.h @@ -238,16 +238,6 @@ struct intel_engine_execlists { */ unsigned int port_mask; - /** - * @switch_priority_hint: Second context priority. - * - * We submit multiple contexts to the HW simultaneously and would - * like to occasionally switch between them to emulate timeslicing. - * To know when timeslicing is suitable, we track the priority of - * the context submitted second. - */ - int switch_priority_hint; - /** * @queue_priority_hint: Highest pending priority. * diff --git a/drivers/gpu/drm/i915/gt/intel_execlists_submission.c b/drivers/gpu/drm/i915/gt/intel_execlists_submission.c index ba3114fd4389..50d4308023f3 100644 --- a/drivers/gpu/drm/i915/gt/intel_execlists_submission.c +++ b/drivers/gpu/drm/i915/gt/intel_execlists_submission.c @@ -1143,25 +1143,6 @@ static void defer_active(struct intel_engine_cs *engine) defer_request(rq, i915_sched_lookup_priolist(engine, rq_prio(rq))); } -static bool -need_timeslice(const struct intel_engine_cs *engine, - const struct i915_request *rq) -{ - int hint; - - if (!intel_engine_has_timeslices(engine)) - return false; - - hint = max(engine->execlists.queue_priority_hint, - virtual_prio(&engine->execlists)); - - if (!list_is_last(&rq->sched.link, &engine->active.requests)) - hint = max(hint, rq_prio(list_next_entry(rq, sched.link))); - - GEM_BUG_ON(hint >= I915_PRIORITY_UNPREEMPTABLE); - return hint >= effective_prio(rq); -} - static bool timeslice_yield(const struct intel_engine_execlists *el, const struct i915_request *rq) @@ -1181,76 +1162,68 @@ timeslice_yield(const struct intel_engine_execlists *el, return rq->context->lrc.ccid == READ_ONCE(el->yield); } -static bool -timeslice_expired(const struct intel_engine_execlists *el, - const struct i915_request *rq) +static bool needs_timeslice(const struct intel_engine_cs *engine, + const struct i915_request *rq) { + if (!intel_engine_has_timeslices(engine)) + return false; + + /* If not currently active, or about to switch, wait for next event */ + if (!rq || __i915_request_is_complete(rq)) + return false; + + /* We do not need to start the timeslice until after the ACK */ + if (READ_ONCE(engine->execlists.pending[0])) + return false; + + /* If ELSP[1] is occupied, always check to see if worth slicing */ + if (!list_is_last_rcu(&rq->sched.link, &engine->active.requests)) + return true; + + /* Otherwise, ELSP[0] is by itself, but may be waiting in the queue */ + if (!RB_EMPTY_ROOT(&engine->execlists.queue.rb_root)) + return true; + + return !RB_EMPTY_ROOT(&engine->execlists.virtual.rb_root); +} + +static bool +timeslice_expired(struct intel_engine_cs *engine, const struct i915_request *rq) +{ + const struct intel_engine_execlists *el = &engine->execlists; + + if (i915_request_has_nopreempt(rq) && __i915_request_has_started(rq)) + return false; + + if (!needs_timeslice(engine, rq)) + return false; + return timer_expired(&el->timer) || timeslice_yield(el, rq); } -static int -switch_prio(struct intel_engine_cs *engine, const struct i915_request *rq) -{ - if (list_is_last(&rq->sched.link, &engine->active.requests)) - return engine->execlists.queue_priority_hint; - - return rq_prio(list_next_entry(rq, sched.link)); -} - -static inline unsigned long -timeslice(const struct intel_engine_cs *engine) +static unsigned long timeslice(const struct intel_engine_cs *engine) { return READ_ONCE(engine->props.timeslice_duration_ms); } -static unsigned long active_timeslice(const struct intel_engine_cs *engine) -{ - const struct intel_engine_execlists *execlists = &engine->execlists; - const struct i915_request *rq = *execlists->active; - - if (!rq || __i915_request_is_complete(rq)) - return 0; - - if (READ_ONCE(execlists->switch_priority_hint) < effective_prio(rq)) - return 0; - - return timeslice(engine); -} - -static void set_timeslice(struct intel_engine_cs *engine) +static void start_timeslice(struct intel_engine_cs *engine) { + struct intel_engine_execlists *el = &engine->execlists; unsigned long duration; - if (!intel_engine_has_timeslices(engine)) - return; + /* Disable the timer if there is nothing to switch to */ + duration = 0; + if (needs_timeslice(engine, *el->active)) { + if (el->timer.expires) { + if (!timer_pending(&el->timer)) + tasklet_hi_schedule(&engine->execlists.tasklet); + return; + } - duration = active_timeslice(engine); - ENGINE_TRACE(engine, "bump timeslicing, interval:%lu", duration); + duration = timeslice(engine); + } - set_timer_ms(&engine->execlists.timer, duration); -} - -static void start_timeslice(struct intel_engine_cs *engine, int prio) -{ - struct intel_engine_execlists *execlists = &engine->execlists; - unsigned long duration; - - if (!intel_engine_has_timeslices(engine)) - return; - - WRITE_ONCE(execlists->switch_priority_hint, prio); - if (prio == INT_MIN) - return; - - if (timer_pending(&execlists->timer)) - return; - - duration = timeslice(engine); - ENGINE_TRACE(engine, - "start timeslicing, prio:%d, interval:%lu", - prio, duration); - - set_timer_ms(&execlists->timer, duration); + set_timer_ms(&el->timer, duration); } static void record_preemption(struct intel_engine_execlists *execlists) @@ -1363,16 +1336,16 @@ static void execlists_dequeue(struct intel_engine_cs *engine) __unwind_incomplete_requests(engine); last = NULL; - } else if (need_timeslice(engine, last) && - timeslice_expired(execlists, last)) { + } else if (timeslice_expired(engine, last)) { ENGINE_TRACE(engine, - "expired last=%llx:%lld, prio=%d, hint=%d, yield?=%s\n", - last->fence.context, - last->fence.seqno, - last->sched.attr.priority, + "expired:%s last=%llx:%lld, prio=%d, hint=%d, yield?=%s\n", + yesno(timer_expired(&execlists->timer)), + last->fence.context, last->fence.seqno, + rq_prio(last), execlists->queue_priority_hint, yesno(timeslice_yield(execlists, last))); + cancel_timer(&execlists->timer); ring_set_paused(engine, 1); defer_active(engine); @@ -1408,7 +1381,6 @@ static void execlists_dequeue(struct intel_engine_cs *engine) * of timeslices, our queue might be. */ spin_unlock(&engine->active.lock); - start_timeslice(engine, queue_prio(execlists)); return; } } @@ -1435,7 +1407,6 @@ static void execlists_dequeue(struct intel_engine_cs *engine) if (last && !can_merge_rq(last, rq)) { spin_unlock(&ve->base.active.lock); spin_unlock(&engine->active.lock); - start_timeslice(engine, rq_prio(rq)); return; /* leave this for another sibling */ } @@ -1599,29 +1570,23 @@ static void execlists_dequeue(struct intel_engine_cs *engine) execlists->queue_priority_hint = queue_prio(execlists); spin_unlock(&engine->active.lock); - if (submit) { - /* - * Skip if we ended up with exactly the same set of requests, - * e.g. trying to timeslice a pair of ordered contexts - */ - if (!memcmp(execlists->active, - execlists->pending, - (port - execlists->pending) * sizeof(*port))) - goto skip_submit; - + /* + * We can skip poking the HW if we ended up with exactly the same set + * of requests as currently running, e.g. trying to timeslice a pair + * of ordered contexts. + */ + if (submit && + memcmp(execlists->active, + execlists->pending, + (port - execlists->pending) * sizeof(*port))) { *port = NULL; while (port-- != execlists->pending) execlists_schedule_in(*port, port - execlists->pending); - execlists->switch_priority_hint = - switch_prio(engine, *execlists->pending); - WRITE_ONCE(execlists->yield, -1); set_preempt_timeout(engine, *execlists->active); execlists_submit_ports(engine); } else { - start_timeslice(engine, execlists->queue_priority_hint); -skip_submit: ring_set_paused(engine, 0); while (port-- != execlists->pending) i915_request_put(*port); @@ -1979,8 +1944,6 @@ process_csb(struct intel_engine_cs *engine, struct i915_request **inactive) } } while (head != tail); - set_timeslice(engine); - /* * Gen11 has proven to fail wrt global observation point between * entry and tail update, failing on the ordering and thus @@ -1993,6 +1956,7 @@ process_csb(struct intel_engine_cs *engine, struct i915_request **inactive) * invalidation before. */ invalidate_csb_entries(&buf[0], &buf[num_entries - 1]); + cancel_timer(&execlists->timer); return inactive; } @@ -2405,8 +2369,10 @@ static void execlists_submission_tasklet(unsigned long data) execlists_reset(engine, msg); } - if (!engine->execlists.pending[0]) + if (!engine->execlists.pending[0]) { execlists_dequeue_irq(engine); + start_timeslice(engine); + } post_process_csb(post, inactive); rcu_read_unlock(); @@ -3851,9 +3817,6 @@ void intel_execlists_show_requests(struct intel_engine_cs *engine, show_request(m, last, "\t\t", 0); } - if (execlists->switch_priority_hint != INT_MIN) - drm_printf(m, "\t\tSwitch priority hint: %d\n", - READ_ONCE(execlists->switch_priority_hint)); if (execlists->queue_priority_hint != INT_MIN) drm_printf(m, "\t\tQueue priority hint: %d\n", READ_ONCE(execlists->queue_priority_hint));
In the next^W future patch, we remove the strict priority system and continuously re-evaluate the relative priority of tasks. As such we need to enable the timeslice whenever there is more than one context in the pipeline. This simplifies the decision and removes some of the tweaks to suppress timeslicing, allowing us to lift the timeslice enabling to a common spot at the end of running the submission tasklet. One consequence of the suppression is that it was reducing fairness between virtual engines on an over saturated system; undermining the principle for timeslicing. Closes: https://gitlab.freedesktop.org/drm/intel/-/issues/2802 Testcase: igt/gem_exec_balancer/fairslice Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> --- drivers/gpu/drm/i915/gt/intel_engine_types.h | 10 - .../drm/i915/gt/intel_execlists_submission.c | 173 +++++++----------- 2 files changed, 68 insertions(+), 115 deletions(-)