changeset d0c2ba70dc12 in /z/repo/gem5
details: http://repo.gem5.org/gem5?cmd=changeset;node=d0c2ba70dc12
description:
cpu: Minor Draining Bug
Fixes a bug where Minor drains in the midst of committing a
conditional store.
While committing a conditional store, lastCommitWasEndOfMacroop is true
(from the previous instruction) as we still haven't finished the
conditional
store. If a drain occurs before the cache response, Minor would check
just
lastCommitWasEndOfMacroop, which was true, and set
drainState=DrainHaltFetch,
which increases the streamSeqNum. This caused the conditional store to
be
squashed when the memory responded and it completed. However, to the
memory
the store succeeded, while to the instruction sequence it never
occurred.
In the case of an LLSC, the instruction sequence will replay the
squashed
STREX, which will fail as the cache is no longer in LLSC. Then the
instruction sequence will loop back to a LDREX, which receives the
updated
(incorrect) value.
Committed by: Nilay Vaish <[email protected]>
diffstat:
src/cpu/minor/execute.cc | 9 +++++----
1 files changed, 5 insertions(+), 4 deletions(-)
diffs (19 lines):
diff -r 0068ad93a67e -r d0c2ba70dc12 src/cpu/minor/execute.cc
--- a/src/cpu/minor/execute.cc Thu Nov 06 05:42:21 2014 -0600
+++ b/src/cpu/minor/execute.cc Thu Nov 06 05:42:21 2014 -0600
@@ -1683,10 +1683,11 @@
if (drainState == NotDraining) {
cpu.wakeupOnEvent(Pipeline::ExecuteStageId);
- /* Go to DrainCurrentInst if we're not between operations
- * this should probably test the LSQ as well. Or maybe
- * just always go to DrainCurrentInst anyway */
- if (lastCommitWasEndOfMacroop)
+ /* Go to DrainCurrentInst if we're between microops
+ * or waiting on an unbufferable memory operation.
+ * Otherwise we can go straight to DrainHaltFetch
+ */
+ if (isInbetweenInsts())
setDrainState(DrainHaltFetch);
else
setDrainState(DrainCurrentInst);
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