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author | Andreas Hansson <andreas.hansson@arm.com> | 2015-09-25 07:13:54 -0400 |
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committer | Andreas Hansson <andreas.hansson@arm.com> | 2015-09-25 07:13:54 -0400 |
commit | 462c288a757bc4fd50324ebe2f1fd697d53838ab (patch) | |
tree | 02cc70a4d0682136b458ee59d5c9dad0dfdec00a /src/mem/coherent_xbar.cc | |
parent | 3bd78a141ec60ae65d910286c3d99ae7030ba703 (diff) | |
download | gem5-462c288a757bc4fd50324ebe2f1fd697d53838ab.tar.xz |
mem: Make the coherent crossbar account for timing snoops
This patch introduces the concept of a snoop latency. Given the
requirement to snoop and forward packets in zero time (due to the
coherency mechanism), the latency is accounted for later.
On a snoop, we establish the latency, and later add it to the header
delay of the packet. To allow multiple caches to contribute to the
snoop latency, we use a separate variable in the packet, and then take
the maximum before adding it to the header delay.
Diffstat (limited to 'src/mem/coherent_xbar.cc')
-rw-r--r-- | src/mem/coherent_xbar.cc | 16 |
1 files changed, 16 insertions, 0 deletions
diff --git a/src/mem/coherent_xbar.cc b/src/mem/coherent_xbar.cc index 52f69e0c9..32ca6d02d 100644 --- a/src/mem/coherent_xbar.cc +++ b/src/mem/coherent_xbar.cc @@ -187,6 +187,8 @@ CoherentXBar::recvTimingReq(PacketPtr pkt, PortID slave_port_id) Tick packetFinishTime = clockEdge(Cycles(1)) + pkt->payloadDelay; if (!system->bypassCaches()) { + assert(pkt->snoopDelay == 0); + // the packet is a memory-mapped request and should be // broadcasted to our snoopers but the source if (snoopFilter) { @@ -204,6 +206,10 @@ CoherentXBar::recvTimingReq(PacketPtr pkt, PortID slave_port_id) } else { forwardTiming(pkt, slave_port_id); } + + // add the snoop delay to our header delay, and then reset it + pkt->headerDelay += pkt->snoopDelay; + pkt->snoopDelay = 0; } // forwardTiming snooped into peer caches of the sender, and if @@ -377,9 +383,15 @@ CoherentXBar::recvTimingSnoopReq(PacketPtr pkt, PortID master_port_id) // we should only see express snoops from caches assert(pkt->isExpressSnoop()); + // set the packet header and payload delay, for now use forward latency + // @todo Assess the choice of latency further + calcPacketTiming(pkt, forwardLatency * clockPeriod()); + // remeber if the packet is inhibited so we can see if it changes const bool is_inhibited = pkt->memInhibitAsserted(); + assert(pkt->snoopDelay == 0); + if (snoopFilter) { // let the Snoop Filter work its magic and guide probing auto sf_res = snoopFilter->lookupSnoop(pkt); @@ -398,6 +410,10 @@ CoherentXBar::recvTimingSnoopReq(PacketPtr pkt, PortID master_port_id) forwardTiming(pkt, InvalidPortID); } + // add the snoop delay to our header delay, and then reset it + pkt->headerDelay += pkt->snoopDelay; + pkt->snoopDelay = 0; + // if we can expect a response, remember how to route it if (!is_inhibited && pkt->memInhibitAsserted()) { assert(routeTo.find(pkt->req) == routeTo.end()); |