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Mem: Fix issue with prefetches originating at non-L1 caches getting stale data

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Prefetch requests issued from the L2 or below wouldn't check if valid data is
present higher in the system. If a prefetch into the L2 occured at the same
time as writeback from a higher-level cache the dirty data could be replaced
in by unmodified data in memory.
This commit is contained in:
Ali Saidi 2011-07-15 11:53:35 -05:00
parent 69ef57fd0f
commit 147095cb08
1 changed files with 38 additions and 1 deletions
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39
src/mem/cache/cache_impl.hh vendored
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@ -420,7 +420,17 @@ Cache<TagStore>::timingAccess(PacketPtr pkt)
// must be cache-to-cache response from upper to lower level
ForwardResponseRecord *rec =
dynamic_cast<ForwardResponseRecord *>(pkt->senderState);
assert(rec != NULL);
if (rec == NULL) {
assert(pkt->cmd == MemCmd::HardPFResp);
// Check if it's a prefetch response and handle it. We shouldn't
// get any other kinds of responses without FRRs.
DPRINTF(Cache, "Got prefetch response from above for addr %#x\n",
pkt->getAddr());
handleResponse(pkt);
return true;
}
rec->restore(pkt, this);
delete rec;
memSidePort->respond(pkt, time);
@ -1472,6 +1482,33 @@ Cache<TagStore>::getTimingPacket()
pkt = tgt_pkt;
} else {
BlkType *blk = tags->findBlock(mshr->addr);
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 copy from memory that might get used
// in place of the dirty one.
PacketPtr snoop_pkt = new Packet(tgt_pkt, true);
snoop_pkt->setExpressSnoop();
snoop_pkt->senderState = mshr;
cpuSidePort->sendTiming(snoop_pkt);
if (snoop_pkt->memInhibitAsserted()) {
markInService(mshr, snoop_pkt);
DPRINTF(Cache, "Upward snoop of prefetch for addr %#x hit\n",
tgt_pkt->getAddr());
delete snoop_pkt;
return NULL;
}
delete snoop_pkt;
}
pkt = getBusPacket(tgt_pkt, blk, mshr->needsExclusive());
mshr->isForward = (pkt == NULL);