Re: [PATCH v2] drm/i915/gen11: Preempt-to-idle support in execlists.

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<snip>

@@ -1010,7 +1033,15 @@ static void execlists_submission_tasklet(unsigned long data)
                                       GEN8_CTX_STATUS_PREEMPTED))
                                 execlists_set_active(execlists,
                                                      EXECLISTS_ACTIVE_HWACK);
-                       if (status & GEN8_CTX_STATUS_ACTIVE_IDLE)
+
+                       /*
+                        * Check if switched to idle or preempted to idle.
+                        * The STATUS_IDLE_ACTIVE flag is really used to mark
+                        * preemtion from idle to idle, this is not a mistake.
+                        */
+                       if ((status & GEN8_CTX_STATUS_ACTIVE_IDLE) ||
+                           ((status & GEN8_CTX_STATUS_IDLE_ACTIVE) &&
+                            (status & GEN11_CTX_STATUS_PREEMPT_IDLE)))
                                 execlists_clear_active(execlists,
                                                        EXECLISTS_ACTIVE_HWACK);

But still pointless, no?


Just to understand, is it pointless because we have a preemption in flight and we're thus going to call execlists_dequeue below, which will eventually clear the flag in execlists_submit_ports? Or do we just don't care if this gets cleared here because we always clear it before a write to the elsp and we're only interested in it being clear between the write and the subsequent csb event?

Also, now that I think about it, with the current flow it doesn't look like we would clear EXECLISTS_ACTIVE_PREEMPT if a preempt-to-idle happens on idle HW, so we still need a condition for that even if we drop the one for EXECLISTS_ACTIVE_HWACK.

Daniele

@@ -1020,8 +1051,13 @@ static void execlists_submission_tasklet(unsigned long data)
                         /* We should never get a COMPLETED | IDLE_ACTIVE! */
                         GEM_BUG_ON(status & GEN8_CTX_STATUS_IDLE_ACTIVE);
- if (status & GEN8_CTX_STATUS_COMPLETE &&
-                           buf[2*head + 1] == execlists->preempt_complete_status) {
+                       /*
+                        * Check if preempted to real idle, either directly or
+                        * the preemptive context already finished executing
+                        */
+                       if ((status & GEN11_CTX_STATUS_PREEMPT_IDLE) ||
+                           (status & GEN8_CTX_STATUS_COMPLETE &&
+                           buf[2*head + 1] == execlists->preempt_complete_status)) {
                                 GEM_TRACE("%s preempt-idle\n", engine->name);
execlists_cancel_port_requests(execlists);
@@ -2157,7 +2193,8 @@ static void execlists_set_default_submission(struct intel_engine_cs *engine)
         engine->unpark = NULL;
engine->flags |= I915_ENGINE_SUPPORTS_STATS;
-       if (engine->i915->preempt_context)
+       if (engine->i915->preempt_context ||
+           HAS_HW_PREEMPT_TO_IDLE(engine->i915))
                 engine->flags |= I915_ENGINE_HAS_PREEMPTION;

-Chris

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