Kyle Roarty has uploaded this change for review. (
https://gem5-review.googlesource.com/c/public/gem5/+/41573 )
Change subject: gpu-compute: Fix accidental execution when stopped at
barrier
......................................................................
gpu-compute: Fix accidental execution when stopped at barrier
Due the compute unit pipeline being executed in reverse order, there
exists a scenario where a compute unit will execute an extra
instruction when it's supposed to be stopped at a barrier. It occurs
as follows:
* The ScheduleStage sets a barrier instruction ready to execute.
* The ScoreboardCheckStage adds another instruction to the readyList.
This is where the barrier is checked, but because the barrier isn't
executing yet, the instruction can be passed along to ScheduleStage
* The barrier executes, and stalls
* The ScheduleStage sees that there's a new instruction and schedules
it to be executed.
* Only now will the ScoreboardCheckStage realize a barrier is active
and stall accordingly
* The subsequent instruction executes
This patch checks for barrier status in the ScheduleStage to prevent
an instruction from being scheduled when there is a barrier active.
Change-Id: Ib683e2c68f361d7ee60a3beaf53b4b6c888c9f8d
---
M src/gpu-compute/schedule_stage.cc
1 file changed, 15 insertions(+), 0 deletions(-)
diff --git a/src/gpu-compute/schedule_stage.cc
b/src/gpu-compute/schedule_stage.cc
index 8a2ea18..5c51e76 100644
--- a/src/gpu-compute/schedule_stage.cc
+++ b/src/gpu-compute/schedule_stage.cc
@@ -106,6 +106,21 @@
wIt++;
}
}
+ /**
+ * Remove any wave that's at a barrier. Due to backwards execution
+ * of the pipeline, the ScoreboardCheckStage can mark an
instruction
+ * as ready immediately before a barrier executes, which would then
+ * be executed when the barrier is active without this check.
+ **/
+ for (auto wIt = fromScoreboardCheck.readyWFs(j).begin();
+ wIt != fromScoreboardCheck.readyWFs(j).end();) {
+ if ((*wIt)->getStatus() == Wavefront::S_BARRIER) {
+ *wIt = nullptr;
+ wIt = fromScoreboardCheck.readyWFs(j).erase(wIt);
+ } else {
+ wIt++;
+ }
+ }
}
// Attempt to add another wave for each EXE type to schList queues
--
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Gerrit-Project: public/gem5
Gerrit-Branch: develop
Gerrit-Change-Id: Ib683e2c68f361d7ee60a3beaf53b4b6c888c9f8d
Gerrit-Change-Number: 41573
Gerrit-PatchSet: 1
Gerrit-Owner: Kyle Roarty <kyleroarty1...@gmail.com>
Gerrit-MessageType: newchange
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