drm/i915/gt: Skip over completed active execlists, again

Now that we are careful to always force-restore contexts upon rewinding
(where necessary), we can restore our optimisation to skip over
completed active execlists when dequeuing.

Referenecs: 35f3fd8182ba ("drm/i915/execlists: Workaround switching back to a completed context")
References: 8ab3a3812aa9 ("drm/i915/gt: Incrementally check for rewinding")
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210120121718.26435-2-chris@chris-wilson.co.uk

diff --git a/drivers/gpu/drm/i915/gt/intel_execlists_submission.c b/drivers/gpu/drm/i915/gt/intel_execlists_submission.c
index 524c8b5..ac1be7a 100644 (file)
--- a/drivers/gpu/drm/i915/gt/intel_execlists_submission.c
+++ b/drivers/gpu/drm/i915/gt/intel_execlists_submission.c
@@ -1224,12 +1224,20 @@ static void set_preempt_timeout(struct intel_engine_cs *engine,
                     active_preempt_timeout(engine, rq));
 }
 
+static bool completed(const struct i915_request *rq)
+{
+       if (i915_request_has_sentinel(rq))
+               return false;
+
+       return __i915_request_is_complete(rq);
+}
+
 static void execlists_dequeue(struct intel_engine_cs *engine)
 {
        struct intel_engine_execlists * const execlists = &engine->execlists;
        struct i915_request **port = execlists->pending;
        struct i915_request ** const last_port = port + execlists->port_mask;
-       struct i915_request *last = *execlists->active;
+       struct i915_request *last, * const *active;
        struct virtual_engine *ve;
        struct rb_node *rb;
        bool submit = false;
@@ -1266,21 +1274,13 @@ static void execlists_dequeue(struct intel_engine_cs *engine)
         * i.e. we will retrigger preemption following the ack in case
         * of trouble.
         *
-        * In theory we can skip over completed contexts that have not
-        * yet been processed by events (as those events are in flight):
-        *
-        * while ((last = *active) && i915_request_completed(last))
-        *      active++;
-        *
-        * However, the GPU cannot handle this as it will ultimately
-        * find itself trying to jump back into a context it has just
-        * completed and barf.
         */
+       active = execlists->active;
+       while ((last = *active) && completed(last))
+               active++;
 
        if (last) {
-               if (__i915_request_is_complete(last)) {
-                       goto check_secondary;
-               } else if (need_preempt(engine, last)) {
+               if (need_preempt(engine, last)) {
                        ENGINE_TRACE(engine,
                                     "preempting last=%llx:%lld, prio=%d, hint=%d\n",
                                     last->fence.context,
@@ -1359,9 +1359,7 @@ static void execlists_dequeue(struct intel_engine_cs *engine)
                         * we hopefully coalesce several updates into a single
                         * submission.
                         */
-check_secondary:
-                       if (!list_is_last(&last->sched.link,
-                                         &engine->active.requests)) {
+                       if (active[1]) {
                                /*
                                 * Even if ELSP[1] is occupied and not worthy
                                 * of timeslices, our queue might be.
@@ -1562,7 +1560,7 @@ done:
         * of ordered contexts.
         */
        if (submit &&
-           memcmp(execlists->active,
+           memcmp(active,
                   execlists->pending,
                   (port - execlists->pending) * sizeof(*port))) {
                *port = NULL;
@@ -1570,7 +1568,7 @@ done:
                        execlists_schedule_in(*port, port - execlists->pending);
 
                WRITE_ONCE(execlists->yield, -1);
-               set_preempt_timeout(engine, *execlists->active);
+               set_preempt_timeout(engine, *active);
                execlists_submit_ports(engine);
        } else {
                ring_set_paused(engine, 0);