mem-cache: Allow tag-only accesses on latency calculation

Some accesses only need to search for a tag in the tag array, with
no need to touch the data array. This is the case for CleanEvicts,
evicts that don't find a corresponding block entry (since a write
cannot be done in parallel with tag lookup), and maintenance
operations.

Change-Id: I7365a915500b5d7ab636d49a9acc627072a7f58e
Signed-off-by: Daniel R. Carvalho <odanrc@yahoo.com.br>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/14878
Reviewed-by: Nikos Nikoleris <nikos.nikoleris@arm.com>
Maintainer: Nikos Nikoleris <nikos.nikoleris@arm.com>

1 files changed, 10 insertions, 0 deletions

diff --git a/src/mem/cache/base.hh b/src/mem/cache/base.hh
index 7bf741144..a7b25ff2f 100644
--- a/src/mem/cache/base.hh
+++ b/src/mem/cache/base.hh
@@ -422,6 +422,16 @@ class BaseCache : public MemObject
     Addr regenerateBlkAddr(CacheBlk* blk);
 
     /**
+     * Calculate latency of accesses that only touch the tag array.
+     * @sa calculateAccessLatency
+     *
+     * @param delay The delay until the packet's metadata is present.
+     * @param lookup_lat Latency of the respective tag lookup.
+     * @return The number of ticks that pass due to a tag-only access.
+     */
+    Cycles calculateTagOnlyLatency(const uint32_t delay,
+                                   const Cycles lookup_lat) const;
+    /**
      * Calculate access latency in ticks given a tag lookup latency, and
      * whether access was a hit or miss.
      *