On 08/05/2018 12:10, Chris Wilson wrote:
Quoting Tvrtko Ursulin (2018-05-08 11:54:27)
On 07/05/2018 14:57, Chris Wilson wrote:
diff --git a/drivers/gpu/drm/i915/i915_irq.c b/drivers/gpu/drm/i915/i915_irq.c
index f9bc3aaa90d0..775cf167d938 100644
--- a/drivers/gpu/drm/i915/i915_irq.c
+++ b/drivers/gpu/drm/i915/i915_irq.c
@@ -1465,19 +1465,18 @@ gen8_cs_irq_handler(struct intel_engine_cs *engine, u32 iir)
struct intel_engine_execlists * const execlists = &engine->execlists;
bool tasklet = false;
- if (iir & GT_CONTEXT_SWITCH_INTERRUPT) {
- if (READ_ONCE(engine->execlists.active))
- tasklet = !test_and_set_bit(ENGINE_IRQ_EXECLIST,
- &engine->irq_posted);
- }
+ if (iir & GT_CONTEXT_SWITCH_INTERRUPT && READ_ONCE(execlists->active))
+ tasklet = !test_and_set_bit(ENGINE_IRQ_EXECLIST,
+ &engine->irq_posted);
if (iir & GT_RENDER_USER_INTERRUPT) {
notify_ring(engine);
- tasklet |= USES_GUC_SUBMISSION(engine->i915);
+ if (!test_bit(ENGINE_IRQ_EXECLIST, &engine->irq_posted))
+ tasklet = USES_GUC_SUBMISSION(engine->i915);
I don't understand this change. In the GuC case IRQ_EXECLISTS is never
set so the conditional is pointeless. In execlist mode user interrupt
has nothing to do with scheduling the tasklet.
Because notify_ring() may have just executed the tasklet and cleared the
bit from irq_posted. I didn't want to then do a second dequeue.
But IRQ_EXECLISTS is never set in GuC mode. So set-if-clear in this case
is equivalent to unconditional-or.
If you want to clear the tasklet bool in execlist mode then this is
extremely non-obvious. More readable owuld be something like
if (iir & USER_IRQ)
tasklet = notify_ring(...) ? 0 : USES_GUC(...);
Where notify_ring would return true if it signalled anything.
We wouldn't know though if that means the tasklet actually ran. :(
Oh well.. put a comment please, because it really is non-obvious.
static void gen8_gt_irq_ack(struct drm_i915_private *i915,
diff --git a/drivers/gpu/drm/i915/intel_guc_submission.c b/drivers/gpu/drm/i915/intel_guc_submission.c
index 6bfe30af7826..7d4542b46f5e 100644
--- a/drivers/gpu/drm/i915/intel_guc_submission.c
+++ b/drivers/gpu/drm/i915/intel_guc_submission.c
@@ -782,6 +782,8 @@ static void guc_submission_tasklet(unsigned long data)
struct execlist_port *port = execlists->port;
struct i915_request *rq;
+ clear_bit(ENGINE_IRQ_EXECLIST, &engine->irq_posted);
+
I don't understand this either - there is no changed code path which
sets this in GuC mode.
The guc may takeover with the bit set. And since we aren't particularly
careful with parking before takeover, it was prudent to always clear it
here as a direct analogue to the execlists context switch handler.
Okay.
Regards,
Tvrtko
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