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.

1 files changed, 13 insertions, 3 deletions

diff --git a/src/mem/xbar.hh b/src/mem/xbar.hh
index f51b08da2..ed678d9d0 100644
--- a/src/mem/xbar.hh
+++ b/src/mem/xbar.hh
@@ -309,8 +309,15 @@ class BaseXBar : public MemObject
         { retry_port->sendRetrySnoopResp(); }
     };
 
-    /** cycles of overhead per transaction */
-    const Cycles headerCycles;
+    /**
+     * Cycles of front-end pipeline including the delay to accept the request
+     * and to decode the address.
+     */
+    const Cycles frontendLatency;
+    /** Cycles of forward latency */
+    const Cycles forwardLatency;
+    /** Cycles of response latency */
+    const Cycles responseLatency;
     /** the width of the xbar in bytes */
     const uint32_t width;
 
@@ -404,8 +411,11 @@ class BaseXBar : public MemObject
      * headerDelay and payloadDelay fields of the packet
      * object with the relative number of ticks required to transmit
      * the header and the payload, respectively.
+     *
+     * @param pkt Packet to populate with timings
+     * @param header_delay Header delay to be added
      */
-    void calcPacketTiming(PacketPtr pkt);
+    void calcPacketTiming(PacketPtr pkt, Tick header_delay);
 
     /**
      * Remember for each of the master ports of the crossbar if we got