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authorSteve Reinhardt <stever@eecs.umich.edu>2007-07-22 08:09:24 -0700
committerSteve Reinhardt <stever@eecs.umich.edu>2007-07-22 08:09:24 -0700
commit1c2d5f5e64387527efe495a59f6946e7b539a543 (patch)
treec830b34dd49bd560da8c1c0dca8855cf5a4777cf
parent1edd143b688e9bd7285344ee8d2f5bd8cb3dc12d (diff)
downloadgem5-1c2d5f5e64387527efe495a59f6946e7b539a543.tar.xz
Replace DeferredSnoop flag with LowerMSHRPending flag.
Turns out DeferredSnoop isn't quite the right bit of info we needed... see new comment in cache_impl.hh. --HG-- extra : convert_revision : a38de8c1677a37acafb743b7074ef88b21d3b7be
-rw-r--r--src/mem/cache/cache.hh3
-rw-r--r--src/mem/cache/cache_impl.hh28
-rw-r--r--src/mem/cache/miss/mshr.cc2
-rw-r--r--src/mem/packet.hh6
4 files changed, 26 insertions, 13 deletions
diff --git a/src/mem/cache/cache.hh b/src/mem/cache/cache.hh
index 57028a05e..7dfe9e8f1 100644
--- a/src/mem/cache/cache.hh
+++ b/src/mem/cache/cache.hh
@@ -190,7 +190,8 @@ class Cache : public BaseCache
* @param new_state The new coherence state for the block.
*/
void handleSnoop(PacketPtr ptk, BlkType *blk,
- bool is_timing, bool is_deferred);
+ bool is_timing, bool is_deferred,
+ bool lower_mshr_pending);
/**
* Create a writeback request for the given block.
diff --git a/src/mem/cache/cache_impl.hh b/src/mem/cache/cache_impl.hh
index c8c1a239c..82410afe1 100644
--- a/src/mem/cache/cache_impl.hh
+++ b/src/mem/cache/cache_impl.hh
@@ -754,7 +754,7 @@ Cache<TagStore>::handleResponse(PacketPtr pkt)
} else {
// response to snoop request
DPRINTF(Cache, "processing deferred snoop...\n");
- handleSnoop(target->pkt, blk, true, true);
+ handleSnoop(target->pkt, blk, true, true, false);
}
mshr->popTarget();
@@ -917,7 +917,8 @@ Cache<TagStore>::doTimingSupplyResponse(PacketPtr req_pkt,
template<class TagStore>
void
Cache<TagStore>::handleSnoop(PacketPtr pkt, BlkType *blk,
- bool is_timing, bool is_deferred)
+ bool is_timing, bool is_deferred,
+ bool lower_mshr_pending)
{
assert(pkt->isRequest());
@@ -929,8 +930,8 @@ Cache<TagStore>::handleSnoop(PacketPtr pkt, BlkType *blk,
if (is_timing) {
Packet *snoopPkt = new Packet(pkt, true); // clear flags
snoopPkt->setExpressSnoop();
- if (is_deferred) {
- snoopPkt->setDeferredSnoop();
+ if (lower_mshr_pending) {
+ snoopPkt->setLowerMSHRPending();
}
snoopPkt->senderState = new ForwardResponseRecord(pkt, this);
cpuSidePort->sendTiming(snoopPkt);
@@ -1017,8 +1018,19 @@ Cache<TagStore>::snoopTiming(PacketPtr pkt)
Addr blk_addr = pkt->getAddr() & ~(Addr(blkSize-1));
MSHR *mshr = mshrQueue.findMatch(blk_addr);
- // better not be snooping a request that conflicts with something
- // we have outstanding...
+
+ // If a lower cache has an operation on this block pending (not
+ // yet in service) on the MSHR, then the upper caches need to know
+ // about it, as this means that the pending operation logically
+ // succeeds the current snoop. It's not sufficient to record
+ // whether the MSHR *is* in service, as this misses the window
+ // where the lower cache has completed the request and the
+ // response is on its way back up the hierarchy.
+ bool lower_mshr_pending =
+ (mshr && (!mshr->inService) || pkt->lowerMSHRPending());
+
+ // Let the MSHR itself track the snoop and decide whether we want
+ // to go ahead and do the regular cache snoop
if (mshr && mshr->handleSnoop(pkt, order++)) {
DPRINTF(Cache, "Deferring snoop on in-service MSHR to blk %x\n",
blk_addr);
@@ -1063,7 +1075,7 @@ Cache<TagStore>::snoopTiming(PacketPtr pkt)
}
}
- handleSnoop(pkt, blk, true, false);
+ handleSnoop(pkt, blk, true, false, lower_mshr_pending);
}
@@ -1078,7 +1090,7 @@ Cache<TagStore>::snoopAtomic(PacketPtr pkt)
}
BlkType *blk = tags->findBlock(pkt->getAddr());
- handleSnoop(pkt, blk, false, false);
+ handleSnoop(pkt, blk, false, false, false);
return hitLatency;
}
diff --git a/src/mem/cache/miss/mshr.cc b/src/mem/cache/miss/mshr.cc
index 856819c10..b9dfdf729 100644
--- a/src/mem/cache/miss/mshr.cc
+++ b/src/mem/cache/miss/mshr.cc
@@ -164,7 +164,7 @@ MSHR::allocateTarget(PacketPtr pkt, Tick whenReady, Counter _order)
bool
MSHR::handleSnoop(PacketPtr pkt, Counter _order)
{
- if (!inService || (pkt->isExpressSnoop() && !pkt->isDeferredSnoop())) {
+ if (!inService || (pkt->isExpressSnoop() && pkt->lowerMSHRPending())) {
// Request has not been issued yet, or it's been issued
// locally but is buffered unissued at some downstream cache
// which is forwarding us this snoop. Either way, the packet
diff --git a/src/mem/packet.hh b/src/mem/packet.hh
index 8063c7ae7..779ea49a2 100644
--- a/src/mem/packet.hh
+++ b/src/mem/packet.hh
@@ -257,7 +257,7 @@ class Packet : public FastAlloc
Shared,
// Special control flags
ExpressSnoop,
- DeferredSnoop,
+ LowerMSHRPending, // not yet in service
NUM_PACKET_FLAGS
};
@@ -323,8 +323,8 @@ class Packet : public FastAlloc
// Special control flags
void setExpressSnoop() { flags[ExpressSnoop] = true; }
bool isExpressSnoop() { return flags[ExpressSnoop]; }
- void setDeferredSnoop() { flags[DeferredSnoop] = true; }
- bool isDeferredSnoop() { return flags[DeferredSnoop]; }
+ void setLowerMSHRPending() { flags[LowerMSHRPending] = true; }
+ bool lowerMSHRPending() { return flags[LowerMSHRPending]; }
// Network error conditions... encapsulate them as methods since
// their encoding keeps changing (from result field to command