diff options
| -rw-r--r-- | src/mem/cache/cache_impl.hh | 27 |
1 files changed, 20 insertions, 7 deletions
diff --git a/src/mem/cache/cache_impl.hh b/src/mem/cache/cache_impl.hh index 9ec0250e1..c671deb68 100644 --- a/src/mem/cache/cache_impl.hh +++ b/src/mem/cache/cache_impl.hh @@ -465,13 +465,17 @@ Cache<TagStore>::recvTimingReq(PacketPtr pkt) promoteWholeLineWrites(pkt); if (pkt->memInhibitAsserted()) { + // a cache above us (but not where the packet came from) is + // responding to the request DPRINTF(Cache, "mem inhibited on 0x%x (%s): not responding\n", pkt->getAddr(), pkt->isSecure() ? "s" : "ns"); assert(!pkt->req->isUncacheable()); - // Special tweak for multilevel coherence: snoop downward here - // on invalidates since there may be other caches below here - // that have shared copies. Not necessary if we know that - // supplier had exclusive copy to begin with. + + // if the packet needs exclusive, and the cache that has + // promised to respond (setting the inhibit flag) is not + // providing exclusive (it is in O vs M state), we know that + // there may be other shared copies in the system; go out and + // invalidate them all if (pkt->needsExclusive() && !pkt->isSupplyExclusive()) { // create a downstream express snoop with cleared packet // flags, there is no need to allocate any data as the @@ -484,21 +488,30 @@ Cache<TagStore>::recvTimingReq(PacketPtr pkt) // make this an instantaneous express snoop, and let the // other caches in the system know that the packet is - // inhibited + // inhibited, because we have found the authorative copy + // (O) that will supply the right data snoop_pkt->setExpressSnoop(); snoop_pkt->assertMemInhibit(); + + // this express snoop travels towards the memory, and at + // every crossbar it is snooped upwards thus reaching + // every cache in the system bool M5_VAR_USED success = memSidePort->sendTimingReq(snoop_pkt); // express snoops always succeed assert(success); + // main memory will delete the packet } - // since we're the official target but we aren't responding, - // delete the packet now. /// @todo nominally we should just delete the packet here, /// however, until 4-phase stuff we can't because sending /// cache is still relying on it pendingDelete.push_back(pkt); + + // no need to take any action in this particular cache as the + // caches along the path to memory are allowed to keep lines + // in a shared state, and a cache above us already committed + // to responding return true; } |