From d35dd71ab4ac44a79ac22dca82277a43cd59f3c6 Mon Sep 17 00:00:00 2001 From: Marco Balboni Date: Mon, 2 Mar 2015 04:00:46 -0500 Subject: mem: Add crossbar latencies This patch introduces latencies in crossbar that were neglected before. In particular, it adds three parameters in crossbar model: front_end_latency, forward_latency, and response_latency. Along with these parameters, three corresponding members are added: frontEndLatency, forwardLatency, and responseLatency. The coherent crossbar has an additional snoop_response_latency. The latency of the request path through the xbar is set as --> frontEndLatency + forwardLatency In case the snoop filter is enabled, the request path latency is charged also by look-up latency of the snoop filter. --> frontEndLatency + SF(lookupLatency) + forwardLatency. The latency of the response path through the xbar is set instead as --> responseLatency. In case of snoop response, if the response is treated as a normal response the latency associated is again --> responseLatency; If instead it is forwarded as snoop response we add an additional variable + snoopResponseLatency and the latency associated is --> snoopResponseLatency; Furthermore, this patch lets the crossbar progress on the next clock edge after an unused retry, changing the time the crossbar considers itself busy after sending a retry that was not acted upon. --- src/mem/noncoherent_xbar.cc | 31 +++++++++++++++++++++++-------- 1 file changed, 23 insertions(+), 8 deletions(-) (limited to 'src/mem/noncoherent_xbar.cc') diff --git a/src/mem/noncoherent_xbar.cc b/src/mem/noncoherent_xbar.cc index db33f0f70..e2bc85cad 100644 --- a/src/mem/noncoherent_xbar.cc +++ b/src/mem/noncoherent_xbar.cc @@ -1,5 +1,5 @@ /* - * Copyright (c) 2011-2014 ARM Limited + * Copyright (c) 2011-2015 ARM Limited * All rights reserved * * The license below extends only to copyright in the software and shall @@ -127,8 +127,17 @@ NoncoherentXBar::recvTimingReq(PacketPtr pkt, PortID slave_port_id) unsigned int pkt_size = pkt->hasData() ? pkt->getSize() : 0; unsigned int pkt_cmd = pkt->cmdToIndex(); - calcPacketTiming(pkt); - Tick packetFinishTime = curTick() + pkt->payloadDelay; + // store the old header delay so we can restore it if needed + Tick old_header_delay = pkt->headerDelay; + + // a request sees the frontend and forward latency + Tick xbar_delay = (frontendLatency + forwardLatency) * clockPeriod(); + + // set the packet header and payload delay + calcPacketTiming(pkt, xbar_delay); + + // determine how long to be crossbar layer is busy + Tick packetFinishTime = clockEdge(Cycles(1)) + pkt->payloadDelay; // before forwarding the packet (and possibly altering it), // remember if we are expecting a response @@ -145,12 +154,12 @@ NoncoherentXBar::recvTimingReq(PacketPtr pkt, PortID slave_port_id) DPRINTF(NoncoherentXBar, "recvTimingReq: src %s %s 0x%x RETRY\n", src_port->name(), pkt->cmdString(), pkt->getAddr()); - // undo the calculation so we can check for 0 again - pkt->headerDelay = pkt->payloadDelay = 0; + // restore the header delay as it is additive + pkt->headerDelay = old_header_delay; // occupy until the header is sent reqLayers[master_port_id]->failedTiming(src_port, - clockEdge(headerCycles)); + clockEdge(Cycles(1))); return false; } @@ -200,8 +209,14 @@ NoncoherentXBar::recvTimingResp(PacketPtr pkt, PortID master_port_id) unsigned int pkt_size = pkt->hasData() ? pkt->getSize() : 0; unsigned int pkt_cmd = pkt->cmdToIndex(); - calcPacketTiming(pkt); - Tick packetFinishTime = curTick() + pkt->payloadDelay; + // a response sees the response latency + Tick xbar_delay = responseLatency * clockPeriod(); + + // set the packet header and payload delay + calcPacketTiming(pkt, xbar_delay); + + // determine how long to be crossbar layer is busy + Tick packetFinishTime = clockEdge(Cycles(1)) + pkt->payloadDelay; // send the packet through the destination slave port bool success M5_VAR_USED = slavePorts[slave_port_id]->sendTimingResp(pkt); -- cgit v1.2.3