mem: Add snoop filters to L2 crossbars, and check size

This patch adds a snoop filter to the L2XBar. For now we refrain from
globally adding a snoop filter to the SystemXBar, since the latter is
also used in systems without caches. In scenarios without caches the
snoop filter will not see any writeback/clean evicts from the CPU
ports, despite the fact that they are snooping. To avoid inadvertent
use of the snoop filter in these cases we leave it out for now.

A size check is added to the snoop filter, merely to ensure it does
not grow beyond the total capacity of the caches above it. The size
has to be set manually, and a value of 8 MByte is choosen as suitably
high default.

1 files changed, 4 insertions, 1 deletions

diff --git a/src/mem/snoop_filter.hh b/src/mem/snoop_filter.hh
index b1e33dc8f..be3018e6e 100755
--- a/src/mem/snoop_filter.hh
+++ b/src/mem/snoop_filter.hh
@@ -90,7 +90,8 @@ class SnoopFilter : public SimObject {
 
     SnoopFilter (const SnoopFilterParams *p) :
         SimObject(p), reqLookupResult(cachedLocations.end()), retryItem{0, 0},
-        linesize(p->system->cacheLineSize()), lookupLatency(p->lookup_latency)
+        linesize(p->system->cacheLineSize()), lookupLatency(p->lookup_latency),
+        maxEntryCount(p->max_capacity / p->system->cacheLineSize())
     {
     }
 
@@ -254,6 +255,8 @@ class SnoopFilter : public SimObject {
     const unsigned linesize;
     /** Latency for doing a lookup in the filter */
     const Cycles lookupLatency;
+    /** Max capacity in terms of cache blocks tracked, for sanity checking */
+    const unsigned maxEntryCount;
 
     /** Statistics */
     Stats::Scalar totRequests;