Quoting Chris Wilson (2018-02-22 14:11:54)
> Sometimes we need to boost the priority of an in-flight request, which
> may lead to the situation where the second submission port then contains
> a higher priority context than the first and so we need to inject a
> preemption event. To do so we must always check inside
> execlists_dequeue() whether there is a priority inversion between the
> ports themselves as well as the head of the priority sorted queue, and we
> cannot just skip dequeuing if the queue is empty.
Michał noted this doesn't extend past 2-port submission as simply as I
thought it might. Nevertheless it does solve the problem we have today
of priority inversion within ELSP[2]. Extending the submission model as
a whole to more ports is left as an exercise to the reader. :|
-Chris
> Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
> Cc: Michał Winiarski <michal.winiarski@xxxxxxxxx>
> Cc: Michel Thierry <michel.thierry@xxxxxxxxx>
> Cc: Mika Kuoppala <mika.kuoppala@xxxxxxxxxxxxxxx>
> Cc: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>
> ---
> drivers/gpu/drm/i915/intel_engine_cs.c | 2 +
> drivers/gpu/drm/i915/intel_guc_submission.c | 17 +--
> drivers/gpu/drm/i915/intel_lrc.c | 161 ++++++++++++++++------------
> drivers/gpu/drm/i915/intel_ringbuffer.h | 5 +
> 4 files changed, 107 insertions(+), 78 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/intel_engine_cs.c b/drivers/gpu/drm/i915/intel_engine_cs.c
> index c31544406974..ce7fcf55ba18 100644
> --- a/drivers/gpu/drm/i915/intel_engine_cs.c
> +++ b/drivers/gpu/drm/i915/intel_engine_cs.c
> @@ -423,6 +423,7 @@ static void intel_engine_init_execlist(struct intel_engine_cs *engine)
> BUILD_BUG_ON_NOT_POWER_OF_2(execlists_num_ports(execlists));
> GEM_BUG_ON(execlists_num_ports(execlists) > EXECLIST_MAX_PORTS);
>
> + execlists->queue_priority = INT_MIN;
> execlists->queue = RB_ROOT;
> execlists->first = NULL;
> }
> @@ -1903,6 +1904,7 @@ void intel_engine_dump(struct intel_engine_cs *engine,
> spin_lock_irq(&engine->timeline->lock);
> list_for_each_entry(rq, &engine->timeline->requests, link)
> print_request(m, rq, " E ");
> + drm_printf(m, " Queue priority: %d\n", execlists->queue_priority);
> for (rb = execlists->first; rb; rb = rb_next(rb)) {
> struct i915_priolist *p =
> rb_entry(rb, typeof(*p), node);
> diff --git a/drivers/gpu/drm/i915/intel_guc_submission.c b/drivers/gpu/drm/i915/intel_guc_submission.c
> index 649113c7a3c2..586dde579903 100644
> --- a/drivers/gpu/drm/i915/intel_guc_submission.c
> +++ b/drivers/gpu/drm/i915/intel_guc_submission.c
> @@ -75,6 +75,11 @@
> *
> */
>
> +static inline struct i915_priolist *to_priolist(struct rb_node *rb)
> +{
> + return rb_entry(rb, struct i915_priolist, node);
> +}
> +
> static inline bool is_high_priority(struct intel_guc_client *client)
> {
> return (client->priority == GUC_CLIENT_PRIORITY_KMD_HIGH ||
> @@ -682,15 +687,12 @@ static void guc_dequeue(struct intel_engine_cs *engine)
> rb = execlists->first;
> GEM_BUG_ON(rb_first(&execlists->queue) != rb);
>
> - if (!rb)
> - goto unlock;
> -
> if (port_isset(port)) {
> if (engine->i915->preempt_context) {
> struct guc_preempt_work *preempt_work =
> &engine->i915->guc.preempt_work[engine->id];
>
> - if (rb_entry(rb, struct i915_priolist, node)->priority >
> + if (execlists->queue_priority >
> max(port_request(port)->priotree.priority, 0)) {
> execlists_set_active(execlists,
> EXECLISTS_ACTIVE_PREEMPT);
> @@ -706,8 +708,8 @@ static void guc_dequeue(struct intel_engine_cs *engine)
> }
> GEM_BUG_ON(port_isset(port));
>
> - do {
> - struct i915_priolist *p = rb_entry(rb, typeof(*p), node);
> + while (rb) {
> + struct i915_priolist *p = to_priolist(rb);
> struct i915_request *rq, *rn;
>
> list_for_each_entry_safe(rq, rn, &p->requests, priotree.link) {
> @@ -736,8 +738,9 @@ static void guc_dequeue(struct intel_engine_cs *engine)
> INIT_LIST_HEAD(&p->requests);
> if (p->priority != I915_PRIORITY_NORMAL)
> kmem_cache_free(engine->i915->priorities, p);
> - } while (rb);
> + }
> done:
> + execlists->queue_priority = rb ? to_priolist(rb)->priority : INT_MIN;
> execlists->first = rb;
> if (submit) {
> port_assign(port, last);
> diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
> index e781c912f197..8a98da7a5c83 100644
> --- a/drivers/gpu/drm/i915/intel_lrc.c
> +++ b/drivers/gpu/drm/i915/intel_lrc.c
> @@ -169,6 +169,23 @@ static void execlists_init_reg_state(u32 *reg_state,
> struct intel_engine_cs *engine,
> struct intel_ring *ring);
>
> +static inline struct i915_priolist *to_priolist(struct rb_node *rb)
> +{
> + return rb_entry(rb, struct i915_priolist, node);
> +}
> +
> +static inline int rq_prio(const struct i915_request *rq)
> +{
> + return rq->priotree.priority;
> +}
> +
> +static inline bool need_preempt(const struct intel_engine_cs *engine,
> + const struct i915_request *last,
> + int prio)
> +{
> + return engine->i915->preempt_context && prio > max(rq_prio(last), 0);
> +}
> +
> /**
> * intel_lr_context_descriptor_update() - calculate & cache the descriptor
> * descriptor for a pinned context
> @@ -224,7 +241,7 @@ lookup_priolist(struct intel_engine_cs *engine,
> parent = &execlists->queue.rb_node;
> while (*parent) {
> rb = *parent;
> - p = rb_entry(rb, typeof(*p), node);
> + p = to_priolist(rb);
> if (prio > p->priority) {
> parent = &rb->rb_left;
> } else if (prio < p->priority) {
> @@ -264,7 +281,7 @@ lookup_priolist(struct intel_engine_cs *engine,
> if (first)
> execlists->first = &p->node;
>
> - return ptr_pack_bits(p, first, 1);
> + return p;
> }
>
> static void unwind_wa_tail(struct i915_request *rq)
> @@ -290,14 +307,10 @@ static void __unwind_incomplete_requests(struct intel_engine_cs *engine)
> __i915_request_unsubmit(rq);
> unwind_wa_tail(rq);
>
> - GEM_BUG_ON(rq->priotree.priority == I915_PRIORITY_INVALID);
> - if (rq->priotree.priority != last_prio) {
> - p = lookup_priolist(engine,
> - &rq->priotree,
> - rq->priotree.priority);
> - p = ptr_mask_bits(p, 1);
> -
> - last_prio = rq->priotree.priority;
> + GEM_BUG_ON(rq_prio(rq) == I915_PRIORITY_INVALID);
> + if (rq_prio(rq) != last_prio) {
> + last_prio = rq_prio(rq);
> + p = lookup_priolist(engine, &rq->priotree, last_prio);
> }
>
> list_add(&rq->priotree.link, &p->requests);
> @@ -397,10 +410,11 @@ static void execlists_submit_ports(struct intel_engine_cs *engine)
> desc = execlists_update_context(rq);
> GEM_DEBUG_EXEC(port[n].context_id = upper_32_bits(desc));
>
> - GEM_TRACE("%s in[%d]: ctx=%d.%d, seqno=%x\n",
> + GEM_TRACE("%s in[%d]: ctx=%d.%d, seqno=%x, prio=%d\n",
> engine->name, n,
> port[n].context_id, count,
> - rq->global_seqno);
> + rq->global_seqno,
> + rq_prio(rq));
> } else {
> GEM_BUG_ON(!n);
> desc = 0;
> @@ -453,12 +467,17 @@ static void inject_preempt_context(struct intel_engine_cs *engine)
> _MASKED_BIT_ENABLE(CTX_CTRL_ENGINE_CTX_RESTORE_INHIBIT |
> CTX_CTRL_ENGINE_CTX_SAVE_INHIBIT));
>
> + /*
> + * Switch to our empty preempt context so
> + * the state of the GPU is known (idle).
> + */
> GEM_TRACE("%s\n", engine->name);
> for (n = execlists_num_ports(&engine->execlists); --n; )
> elsp_write(0, engine->execlists.elsp);
>
> elsp_write(ce->lrc_desc, engine->execlists.elsp);
> execlists_clear_active(&engine->execlists, EXECLISTS_ACTIVE_HWACK);
> + execlists_set_active(&engine->execlists, EXECLISTS_ACTIVE_PREEMPT);
> }
>
> static void execlists_dequeue(struct intel_engine_cs *engine)
> @@ -495,8 +514,6 @@ static void execlists_dequeue(struct intel_engine_cs *engine)
> spin_lock_irq(&engine->timeline->lock);
> rb = execlists->first;
> GEM_BUG_ON(rb_first(&execlists->queue) != rb);
> - if (!rb)
> - goto unlock;
>
> if (last) {
> /*
> @@ -519,54 +536,48 @@ static void execlists_dequeue(struct intel_engine_cs *engine)
> if (!execlists_is_active(execlists, EXECLISTS_ACTIVE_HWACK))
> goto unlock;
>
> - if (engine->i915->preempt_context &&
> - rb_entry(rb, struct i915_priolist, node)->priority >
> - max(last->priotree.priority, 0)) {
> - /*
> - * Switch to our empty preempt context so
> - * the state of the GPU is known (idle).
> - */
> + if (need_preempt(engine, last, execlists->queue_priority)) {
> inject_preempt_context(engine);
> - execlists_set_active(execlists,
> - EXECLISTS_ACTIVE_PREEMPT);
> goto unlock;
> - } else {
> - /*
> - * In theory, we could coalesce more requests onto
> - * the second port (the first port is active, with
> - * no preemptions pending). However, that means we
> - * then have to deal with the possible lite-restore
> - * of the second port (as we submit the ELSP, there
> - * may be a context-switch) but also we may complete
> - * the resubmission before the context-switch. Ergo,
> - * coalescing onto the second port will cause a
> - * preemption event, but we cannot predict whether
> - * that will affect port[0] or port[1].
> - *
> - * If the second port is already active, we can wait
> - * until the next context-switch before contemplating
> - * new requests. The GPU will be busy and we should be
> - * able to resubmit the new ELSP before it idles,
> - * avoiding pipeline bubbles (momentary pauses where
> - * the driver is unable to keep up the supply of new
> - * work).
> - */
> - if (port_count(&port[1]))
> - goto unlock;
> -
> - /* WaIdleLiteRestore:bdw,skl
> - * Apply the wa NOOPs to prevent
> - * ring:HEAD == rq:TAIL as we resubmit the
> - * request. See gen8_emit_breadcrumb() for
> - * where we prepare the padding after the
> - * end of the request.
> - */
> - last->tail = last->wa_tail;
> }
> +
> + /*
> + * In theory, we could coalesce more requests onto
> + * the second port (the first port is active, with
> + * no preemptions pending). However, that means we
> + * then have to deal with the possible lite-restore
> + * of the second port (as we submit the ELSP, there
> + * may be a context-switch) but also we may complete
> + * the resubmission before the context-switch. Ergo,
> + * coalescing onto the second port will cause a
> + * preemption event, but we cannot predict whether
> + * that will affect port[0] or port[1].
> + *
> + * If the second port is already active, we can wait
> + * until the next context-switch before contemplating
> + * new requests. The GPU will be busy and we should be
> + * able to resubmit the new ELSP before it idles,
> + * avoiding pipeline bubbles (momentary pauses where
> + * the driver is unable to keep up the supply of new
> + * work). However, we have to double check that the
> + * priorities of the ports haven't been switch.
> + */
> + if (port_count(&port[1]))
> + goto unlock;
> +
> + /*
> + * WaIdleLiteRestore:bdw,skl
> + * Apply the wa NOOPs to prevent
> + * ring:HEAD == rq:TAIL as we resubmit the
> + * request. See gen8_emit_breadcrumb() for
> + * where we prepare the padding after the
> + * end of the request.
> + */
> + last->tail = last->wa_tail;
> }
>
> - do {
> - struct i915_priolist *p = rb_entry(rb, typeof(*p), node);
> + while (rb) {
> + struct i915_priolist *p = to_priolist(rb);
> struct i915_request *rq, *rn;
>
> list_for_each_entry_safe(rq, rn, &p->requests, priotree.link) {
> @@ -628,8 +639,9 @@ static void execlists_dequeue(struct intel_engine_cs *engine)
> INIT_LIST_HEAD(&p->requests);
> if (p->priority != I915_PRIORITY_NORMAL)
> kmem_cache_free(engine->i915->priorities, p);
> - } while (rb);
> + }
> done:
> + execlists->queue_priority = rb ? to_priolist(rb)->priority : INT_MIN;
> execlists->first = rb;
> if (submit)
> port_assign(port, last);
> @@ -690,7 +702,7 @@ static void execlists_cancel_requests(struct intel_engine_cs *engine)
> /* Flush the queued requests to the timeline list (for retiring). */
> rb = execlists->first;
> while (rb) {
> - struct i915_priolist *p = rb_entry(rb, typeof(*p), node);
> + struct i915_priolist *p = to_priolist(rb);
>
> list_for_each_entry_safe(rq, rn, &p->requests, priotree.link) {
> INIT_LIST_HEAD(&rq->priotree.link);
> @@ -708,7 +720,7 @@ 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->queue = RB_ROOT;
> execlists->first = NULL;
> GEM_BUG_ON(port_isset(execlists->port));
> @@ -867,10 +879,11 @@ static void execlists_submission_tasklet(unsigned long data)
> GEM_DEBUG_BUG_ON(buf[2 * head + 1] != port->context_id);
>
> rq = port_unpack(port, &count);
> - GEM_TRACE("%s out[0]: ctx=%d.%d, seqno=%x\n",
> + GEM_TRACE("%s out[0]: ctx=%d.%d, seqno=%x, prio=%d\n",
> engine->name,
> port->context_id, count,
> - rq ? rq->global_seqno : 0);
> + rq ? rq->global_seqno : 0,
> + rq ? rq_prio(rq) : 0);
> GEM_BUG_ON(count == 0);
> if (--count == 0) {
> GEM_BUG_ON(status & GEN8_CTX_STATUS_PREEMPTED);
> @@ -908,15 +921,19 @@ static void execlists_submission_tasklet(unsigned long data)
> intel_uncore_forcewake_put(dev_priv, execlists->fw_domains);
> }
>
> -static void insert_request(struct intel_engine_cs *engine,
> - struct i915_priotree *pt,
> - int prio)
> +static void queue_request(struct intel_engine_cs *engine,
> + struct i915_priotree *pt,
> + int prio)
> {
> - struct i915_priolist *p = lookup_priolist(engine, pt, prio);
> + list_add_tail(&pt->link, &lookup_priolist(engine, pt, prio)->requests);
> +}
>
> - list_add_tail(&pt->link, &ptr_mask_bits(p, 1)->requests);
> - if (ptr_unmask_bits(p, 1))
> +static void submit_queue(struct intel_engine_cs *engine, int prio)
> +{
> + if (prio > engine->execlists.queue_priority) {
> + engine->execlists.queue_priority = prio;
> tasklet_hi_schedule(&engine->execlists.tasklet);
> + }
> }
>
> static void execlists_submit_request(struct i915_request *request)
> @@ -927,7 +944,8 @@ static void execlists_submit_request(struct i915_request *request)
> /* Will be called from irq-context when using foreign fences. */
> spin_lock_irqsave(&engine->timeline->lock, flags);
>
> - insert_request(engine, &request->priotree, request->priotree.priority);
> + queue_request(engine, &request->priotree, rq_prio(request));
> + submit_queue(engine, rq_prio(request));
>
> GEM_BUG_ON(!engine->execlists.first);
> GEM_BUG_ON(list_empty(&request->priotree.link));
> @@ -983,7 +1001,7 @@ static void execlists_schedule(struct i915_request *request, int prio)
> * static void update_priorities(struct i915_priotree *pt, prio) {
> * list_for_each_entry(dep, &pt->signalers_list, signal_link)
> * update_priorities(dep->signal, prio)
> - * insert_request(pt);
> + * queue_request(pt);
> * }
> * but that may have unlimited recursion depth and so runs a very
> * real risk of overunning the kernel stack. Instead, we build
> @@ -1046,8 +1064,9 @@ static void execlists_schedule(struct i915_request *request, int prio)
> pt->priority = prio;
> if (!list_empty(&pt->link)) {
> __list_del_entry(&pt->link);
> - insert_request(engine, pt, prio);
> + queue_request(engine, pt, prio);
> }
> + submit_queue(engine, prio);
> }
>
> spin_unlock_irq(&engine->timeline->lock);
> diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.h b/drivers/gpu/drm/i915/intel_ringbuffer.h
> index a9b83bf7e837..c4e9022b34e3 100644
> --- a/drivers/gpu/drm/i915/intel_ringbuffer.h
> +++ b/drivers/gpu/drm/i915/intel_ringbuffer.h
> @@ -257,6 +257,11 @@ struct intel_engine_execlists {
> */
> unsigned int port_mask;
>
> + /**
> + * @queue_priority: Highest pending priority.
> + */
> + int queue_priority;
> +
> /**
> * @queue: queue of requests, in priority lists
> */
> --
> 2.16.1
>
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