changeset aa8fd8f6a495 in /z/repo/m5
details: http://repo.m5sim.org/m5?cmd=changeset;node=aa8fd8f6a495
description:
cache: coherence protocol enhancements & bug fixes
Allow lower-level caches (e.g., L2 or L3) to pass exclusive
copies to higher levels (e.g., L1). This eliminates a lot
of unnecessary upgrade transactions on read-write sequences
to non-shared data.
Also some cleanup of MSHR coherence handling and multiple
bug fixes.
diffstat:
src/mem/cache/base.hh | 4 +-
src/mem/cache/cache.hh | 6 +-
src/mem/cache/cache_impl.hh | 82 +++++++++++++++++++++++++++++--------
src/mem/cache/mshr.cc | 97 +++++++++++++++++++++++---------------------
src/mem/cache/mshr.hh | 26 ++++++++++-
src/mem/cache/mshr_queue.cc | 4 +-
src/mem/cache/mshr_queue.hh | 2 +-
7 files changed, 146 insertions(+), 75 deletions(-)
diffs (truncated from 493 to 300 lines):
diff -r c1b66fc648e2 -r aa8fd8f6a495 src/mem/cache/base.hh
--- a/src/mem/cache/base.hh Tue Aug 31 09:50:49 2010 -0700
+++ b/src/mem/cache/base.hh Thu Sep 09 14:40:18 2010 -0400
@@ -170,11 +170,11 @@
return mshr;
}
- void markInServiceInternal(MSHR *mshr)
+ void markInServiceInternal(MSHR *mshr, PacketPtr pkt)
{
MSHRQueue *mq = mshr->queue;
bool wasFull = mq->isFull();
- mq->markInService(mshr);
+ mq->markInService(mshr, pkt);
if (wasFull && !mq->isFull()) {
clearBlocked((BlockedCause)mq->index);
}
diff -r c1b66fc648e2 -r aa8fd8f6a495 src/mem/cache/cache.hh
--- a/src/mem/cache/cache.hh Tue Aug 31 09:50:49 2010 -0700
+++ b/src/mem/cache/cache.hh Thu Sep 09 14:40:18 2010 -0400
@@ -178,7 +178,9 @@
BlkType *handleFill(PacketPtr pkt, BlkType *blk,
PacketList &writebacks);
- void satisfyCpuSideRequest(PacketPtr pkt, BlkType *blk);
+ void satisfyCpuSideRequest(PacketPtr pkt, BlkType *blk,
+ bool deferred_response = false,
+ bool pending_downgrade = false);
bool satisfyMSHR(MSHR *mshr, PacketPtr pkt, BlkType *blk);
void doTimingSupplyResponse(PacketPtr req_pkt, uint8_t *blk_data,
@@ -292,7 +294,7 @@
* are successfully sent.
* @param pkt The request that was sent on the bus.
*/
- void markInService(MSHR *mshr);
+ void markInService(MSHR *mshr, PacketPtr pkt = 0);
/**
* Perform the given writeback request.
diff -r c1b66fc648e2 -r aa8fd8f6a495 src/mem/cache/cache_impl.hh
--- a/src/mem/cache/cache_impl.hh Tue Aug 31 09:50:49 2010 -0700
+++ b/src/mem/cache/cache_impl.hh Thu Sep 09 14:40:18 2010 -0400
@@ -165,16 +165,18 @@
template<class TagStore>
void
-Cache<TagStore>::satisfyCpuSideRequest(PacketPtr pkt, BlkType *blk)
+Cache<TagStore>::satisfyCpuSideRequest(PacketPtr pkt, BlkType *blk,
+ bool deferred_response,
+ bool pending_downgrade)
{
- assert(blk);
+ assert(blk && blk->isValid());
// Occasionally this is not true... if we are a lower-level cache
// satisfying a string of Read and ReadEx requests from
// upper-level caches, a Read will mark the block as shared but we
// can satisfy a following ReadEx anyway since we can rely on the
// Read requester(s) to have buffered the ReadEx snoop and to
// invalidate their blocks after receiving them.
- // assert(pkt->needsExclusive() ? blk->isWritable() : blk->isValid());
+ // assert(!pkt->needsExclusive() || blk->isWritable());
assert(pkt->getOffset(blkSize) + pkt->getSize() <= blkSize);
// Check RMW operations first since both isRead() and
@@ -195,13 +197,43 @@
// special handling for coherent block requests from
// upper-level caches
if (pkt->needsExclusive()) {
- // on ReadExReq we give up our copy
+ // if we have a dirty copy, make sure the recipient
+ // keeps it marked dirty
+ if (blk->isDirty()) {
+ pkt->assertMemInhibit();
+ }
+ // on ReadExReq we give up our copy unconditionally
tags->invalidateBlk(blk);
+ } else if (blk->isWritable() && !pending_downgrade
+ && !pkt->sharedAsserted()) {
+ // we can give the requester an exclusive copy (by not
+ // asserting shared line) on a read request if:
+ // - we have an exclusive copy at this level (& below)
+ // - we don't have a pending snoop from below
+ // signaling another read request
+ // - no other cache above has a copy (otherwise it
+ // would have asseretd shared line on request)
+
+ if (blk->isDirty()) {
+ // special considerations if we're owner:
+ if (!deferred_response) {
+ // if we are responding immediately and can
+ // signal that we're transferring ownership
+ // along with exclusivity, do so
+ pkt->assertMemInhibit();
+ blk->status &= ~BlkDirty;
+ } else {
+ // if we're responding after our own miss,
+ // there's a window where the recipient didn't
+ // know it was getting ownership and may not
+ // have responded to snoops correctly, so we
+ // can't pass off ownership *or* exclusivity
+ pkt->assertShared();
+ }
+ }
} else {
- // on ReadReq we create shareable copies here and in
- // the requester
+ // otherwise only respond with a shared copy
pkt->assertShared();
- blk->status &= ~BlkWritable;
}
}
} else {
@@ -223,9 +255,9 @@
template<class TagStore>
void
-Cache<TagStore>::markInService(MSHR *mshr)
+Cache<TagStore>::markInService(MSHR *mshr, PacketPtr pkt)
{
- markInServiceInternal(mshr);
+ markInServiceInternal(mshr, pkt);
#if 0
if (mshr->originalCmd == MemCmd::HardPFReq) {
DPRINTF(HWPrefetch, "%s:Marking a HW_PF in service\n",
@@ -829,7 +861,8 @@
case MSHR::Target::FromCPU:
Tick completion_time;
if (is_fill) {
- satisfyCpuSideRequest(target->pkt, blk);
+ satisfyCpuSideRequest(target->pkt, blk,
+ true, mshr->hasPostDowngrade());
// How many bytes past the first request is this one
int transfer_offset =
target->pkt->getOffset(blkSize) - initial_offset;
@@ -860,12 +893,11 @@
// if this packet is an error copy that to the new packet
if (is_error)
target->pkt->copyError(pkt);
- if (pkt->isInvalidate()) {
+ if (target->pkt->cmd == MemCmd::ReadResp &&
+ (pkt->isInvalidate() || mshr->hasPostInvalidate())) {
// If intermediate cache got ReadRespWithInvalidate,
// propagate that. Response should not have
// isInvalidate() set otherwise.
- assert(target->pkt->cmd == MemCmd::ReadResp);
- assert(pkt->cmd == MemCmd::ReadRespWithInvalidate);
target->pkt->cmd = MemCmd::ReadRespWithInvalidate;
}
cpuSidePort->respond(target->pkt, completion_time);
@@ -884,8 +916,9 @@
assert(!is_error);
// response to snoop request
DPRINTF(Cache, "processing deferred snoop...\n");
+ assert(!(pkt->isInvalidate() && !mshr->hasPostInvalidate()));
handleSnoop(target->pkt, blk, true, true,
- mshr->pendingInvalidate || pkt->isInvalidate());
+ mshr->hasPostInvalidate());
break;
default:
@@ -895,14 +928,20 @@
mshr->popTarget();
}
- if (pkt->isInvalidate()) {
- tags->invalidateBlk(blk);
+ if (blk) {
+ if (pkt->isInvalidate() || mshr->hasPostInvalidate()) {
+ tags->invalidateBlk(blk);
+ } else if (mshr->hasPostDowngrade()) {
+ blk->status &= ~BlkWritable;
+ }
}
if (mshr->promoteDeferredTargets()) {
// avoid later read getting stale data while write miss is
// outstanding.. see comment in timingAccess()
- blk->status &= ~BlkReadable;
+ if (blk) {
+ blk->status &= ~BlkReadable;
+ }
MSHRQueue *mq = mshr->queue;
mq->markPending(mshr);
requestMemSideBus((RequestCause)mq->index, pkt->finishTime);
@@ -1017,14 +1056,19 @@
int id = pkt->req->hasContextId() ? pkt->req->contextId() : -1;
tags->insertBlock(pkt->getAddr(), blk, id);
}
+
+ // starting from scratch with a new block
+ blk->status = 0;
} else {
// existing block... probably an upgrade
assert(blk->tag == tags->extractTag(addr));
// either we're getting new data or the block should already be valid
assert(pkt->hasData() || blk->isValid());
+ // don't clear block status... if block is already dirty we
+ // don't want to lose that
}
- blk->status = BlkValid | BlkReadable;
+ blk->status |= BlkValid | BlkReadable;
if (!pkt->sharedAsserted()) {
blk->status |= BlkWritable;
@@ -1587,7 +1631,7 @@
delete pkt;
}
} else {
- myCache()->markInService(mshr);
+ myCache()->markInService(mshr, pkt);
}
}
}
diff -r c1b66fc648e2 -r aa8fd8f6a495 src/mem/cache/mshr.cc
--- a/src/mem/cache/mshr.cc Tue Aug 31 09:50:49 2010 -0700
+++ b/src/mem/cache/mshr.cc Thu Sep 09 14:40:18 2010 -0400
@@ -89,6 +89,19 @@
}
+static void
+replaceUpgrade(PacketPtr pkt)
+{
+ if (pkt->cmd == MemCmd::UpgradeReq) {
+ pkt->cmd = MemCmd::ReadExReq;
+ DPRINTF(Cache, "Replacing UpgradeReq with ReadExReq\n");
+ } else if (pkt->cmd == MemCmd::SCUpgradeReq) {
+ pkt->cmd = MemCmd::SCUpgradeFailReq;
+ DPRINTF(Cache, "Replacing SCUpgradeReq with SCUpgradeFailReq\n");
+ }
+}
+
+
void
MSHR::TargetList::replaceUpgrades()
{
@@ -97,13 +110,7 @@
Iterator end_i = end();
for (Iterator i = begin(); i != end_i; ++i) {
- if (i->pkt->cmd == MemCmd::UpgradeReq) {
- i->pkt->cmd = MemCmd::ReadExReq;
- DPRINTF(Cache, "Replacing UpgradeReq with ReadExReq\n");
- } else if (i->pkt->cmd == MemCmd::SCUpgradeReq) {
- i->pkt->cmd = MemCmd::SCUpgradeFailReq;
- DPRINTF(Cache, "Replacing SCUpgradeReq with SCUpgradeFailReq\n");
- }
+ replaceUpgrade(i->pkt);
}
hasUpgrade = false;
@@ -180,8 +187,6 @@
Target::FromPrefetcher : Target::FromCPU;
targets->add(target, whenReady, _order, source, true);
assert(deferredTargets->isReset());
- pendingInvalidate = false;
- pendingShared = false;
data = NULL;
}
@@ -197,7 +202,7 @@
}
bool
-MSHR::markInService()
+MSHR::markInService(PacketPtr pkt)
{
assert(!inService);
if (isForwardNoResponse()) {
@@ -208,6 +213,10 @@
return true;
}
inService = true;
+ pendingDirty = (targets->needsExclusive ||
+ (!pkt->sharedAsserted() && pkt->memInhibitAsserted()));
+ postInvalidate = postDowngrade = false;
+
if (!downstreamPending) {
// let upstream caches know that the request has made it to a
// level where it's going to get a response
@@ -225,8 +234,6 @@
assert(deferredTargets->isReset());
assert(ntargets == 0);
inService = false;
- //allocIter = NULL;
- //readyIter = NULL;
}
/*
@@ -241,17 +248,22 @@
// - there are other targets already deferred
// - there's a pending invalidate to be applied after the response
// comes back (but before this target is processed)
- // - the outstanding request is for a non-exclusive block and this
- // target requires an exclusive block
+ // - this target requires an exclusive block and either we're not
+ // getting an exclusive block back or we have already snooped
+ // another read request that will downgrade our exclusive block
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