mem-cache: Add stats for failed compressions

Add statistics to keep track of the number of times compression
has failed to provide blocks whose compressed size passes the
size threshold.

Also, update the compressed data's size if compression fails.

Change-Id: If3479572bf114f07911238c602ffef3a90b6a931
Signed-off-by: Daniel R. Carvalho <odanrc@yahoo.com.br>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/33384
Reviewed-by: Nikos Nikoleris <nikos.nikoleris@arm.com>
Maintainer: Nikos Nikoleris <nikos.nikoleris@arm.com>
Tested-by: kokoro <noreply+kokoro@google.com>

src/mem/cache/compressors/base.cc

@@ -148,6 +148,7 @@ Base::compress(const uint64_t* data, Cycles& comp_lat, Cycles& decomp_lat)
     if (comp_size_bits > sizeThreshold * CHAR_BIT) {
         comp_size_bits = blkSize * CHAR_BIT;
         comp_data->setSizeBits(comp_size_bits);
+        stats.failedCompressions++;
     }
 
     // Update stats
@@ -209,6 +210,8 @@ Base::BaseStats::BaseStats(Base& _compressor)
   : Stats::Group(&_compressor), compressor(_compressor),
     compressions(this, "compressions",
         "Total number of compressions"),
+    failedCompressions(this, "failed_compressions",
+        "Total number of failed compressions"),
     compressionSize(this, "compression_size",
         "Number of blocks that were compressed to this power of two size"),
     compressionSizeBits(this, "compression_size_bits",

src/mem/cache/compressors/base.hh

@@ -106,6 +106,9 @@ class Base : public SimObject
         /** Number of compressions performed. */
         Stats::Scalar compressions;
 
+        /** Number of failed compressions. */
+        Stats::Scalar failedCompressions;
+
         /** Number of blocks that were compressed to this power of two size. */
         Stats::Vector compressionSize;