changeset 97aa1ee1c2d9 in /z/repo/gem5
details: http://repo.gem5.org/gem5?cmd=changeset;node=97aa1ee1c2d9
description:
mem: Fix bug relating to writebacks and prefetches
Previously the code commented about an unhandled case where it might be
possible for a writeback to arrive after a prefetch was generated but
before it was sent to the memory system. I hit that case. Luckily
the prefetchSquash() logic already in the code handles dropping prefetch
request in certian circumstances.
diffstat:
src/mem/cache/cache_impl.hh | 12 ++++--------
1 files changed, 4 insertions(+), 8 deletions(-)
diffs (29 lines):
diff -r b9646f4546ad -r 97aa1ee1c2d9 src/mem/cache/cache_impl.hh
--- a/src/mem/cache/cache_impl.hh Tue Dec 23 09:31:18 2014 -0500
+++ b/src/mem/cache/cache_impl.hh Tue Dec 23 09:31:18 2014 -0500
@@ -1892,12 +1892,6 @@
BlkType *blk = tags->findBlock(mshr->addr, mshr->isSecure);
if (tgt_pkt->cmd == MemCmd::HardPFReq) {
- // It might be possible for a writeback to arrive between
- // the time the prefetch is placed in the MSHRs and when
- // it's selected to send... if so, this assert will catch
- // that, and then we'll have to figure out what to do.
- assert(blk == NULL);
-
// We need to check the caches above us to verify that
// they don't have a copy of this block in the dirty state
// at the moment. Without this check we could get a stale
@@ -1909,8 +1903,10 @@
cpuSidePort->sendTimingSnoopReq(&snoop_pkt);
// Check to see if the prefetch was squashed by an upper cache
- if (snoop_pkt.prefetchSquashed()) {
- DPRINTF(Cache, "Prefetch squashed by upper cache. "
+ // Or if a writeback arrived between the time the prefetch was
+ // placed in the MSHRs and when it was selected to send.
+ if (snoop_pkt.prefetchSquashed() || blk != NULL) {
+ DPRINTF(Cache, "Prefetch squashed by cache. "
"Deallocating mshr target %#x.\n", mshr->addr);
// Deallocate the mshr target
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