Matt Sinclair has submitted this change. (
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 sets the wavefront status to be S_BARRIER in ScheduleStage
instead of in the barrier instruction execution in order to have
ScoreboardCheckStage realize that we're going to execute a barrier,
preventing it from marking another instruciton as ready.
Change-Id: Ib683e2c68f361d7ee60a3beaf53b4b6c888c9f8d
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/41573
Reviewed-by: Matt Sinclair <mattdsincl...@gmail.com>
Reviewed-by: Alexandru Duțu <alexandru.d...@amd.com>
Maintainer: Matt Sinclair <mattdsincl...@gmail.com>
Tested-by: kokoro <noreply+kok...@google.com>
---
M src/arch/gcn3/insts/instructions.cc
M src/gpu-compute/schedule_stage.cc
2 files changed, 3 insertions(+), 2 deletions(-)
Approvals:
Alexandru Duțu: Looks good to me, approved
Matt Sinclair: Looks good to me, but someone else must approve; Looks
good to me, approved
kokoro: Regressions pass
diff --git a/src/arch/gcn3/insts/instructions.cc
b/src/arch/gcn3/insts/instructions.cc
index 29de1a8..bde87ef 100644
--- a/src/arch/gcn3/insts/instructions.cc
+++ b/src/arch/gcn3/insts/instructions.cc
@@ -4114,8 +4114,6 @@
if (wf->hasBarrier()) {
int bar_id = wf->barrierId();
- assert(wf->getStatus() != Wavefront::S_BARRIER);
- wf->setStatus(Wavefront::S_BARRIER);
cu->incNumAtBarrier(bar_id);
DPRINTF(GPUSync, "CU[%d] WF[%d][%d] Wave[%d] - Stalling at "
"barrier Id%d. %d waves now at barrier, %d waves "
diff --git a/src/gpu-compute/schedule_stage.cc
b/src/gpu-compute/schedule_stage.cc
index 8a2ea18..ace6d0c 100644
--- a/src/gpu-compute/schedule_stage.cc
+++ b/src/gpu-compute/schedule_stage.cc
@@ -314,6 +314,9 @@
computeUnit.insertInPipeMap(wf);
wavesInSch.emplace(wf->wfDynId);
schList.at(exeType).push_back(std::make_pair(gpu_dyn_inst,
RFBUSY));
+ if (wf->isOldestInstBarrier() && wf->hasBarrier()) {
+ wf->setStatus(Wavefront::S_BARRIER);
+ }
if (wf->isOldestInstWaitcnt()) {
wf->setStatus(Wavefront::S_WAITCNT);
}
--
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Gerrit-Project: public/gem5
Gerrit-Branch: release-staging-v21-0
Gerrit-Change-Id: Ib683e2c68f361d7ee60a3beaf53b4b6c888c9f8d
Gerrit-Change-Number: 41573
Gerrit-PatchSet: 4
Gerrit-Owner: Kyle Roarty <kyleroarty1...@gmail.com>
Gerrit-Reviewer: Alexandru Duțu <alexandru.d...@amd.com>
Gerrit-Reviewer: Matt Sinclair <mattdsincl...@gmail.com>
Gerrit-Reviewer: Matthew Poremba <matthew.pore...@amd.com>
Gerrit-Reviewer: kokoro <noreply+kok...@google.com>
Gerrit-CC: Bobby R. Bruce <bbr...@ucdavis.edu>
Gerrit-MessageType: merged
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