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, 4 insertions, 1 deletions

diff --git a/src/mem/coherent_xbar.hh b/src/mem/coherent_xbar.hh
index ffe4a066b..3cf10689c 100644
--- a/src/mem/coherent_xbar.hh
+++ b/src/mem/coherent_xbar.hh
@@ -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
@@ -272,6 +272,9 @@ class CoherentXBar : public BaseXBar
       * broadcast needed for probes.  NULL denotes an absent filter. */
     SnoopFilter *snoopFilter;
 
+    /** Cycles of snoop response latency.*/
+    const Cycles snoopResponseLatency;
+
     /** Function called by the port when the crossbar is recieving a Timing
       request packet.*/
     bool recvTimingReq(PacketPtr pkt, PortID slave_port_id);