Daniel Carvalho has submitted this change. (
https://gem5-review.googlesource.com/c/public/gem5/+/33383 )
Change subject: mem-cache: Handle zero sizes on compression
......................................................................
mem-cache: Handle zero sizes on compression
The size can be zero in special occasions, which would
generate divisions by zero. This patch expands the
stats to support them. It also fixes the compression
factor calculation in the Multi compressor.
As a side effect, now that zero sizes are handled, allow
the Zero compressor to generate it.
Change-Id: I9f7dee76576b09fdc9bef3e1f3f89be3726dcbd9
Signed-off-by: Daniel R. Carvalho <[email protected]>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/33383
Reviewed-by: Nikos Nikoleris <[email protected]>
Maintainer: Nikos Nikoleris <[email protected]>
Tested-by: kokoro <[email protected]>
---
M src/mem/cache/compressors/base.cc
M src/mem/cache/compressors/multi.cc
M src/mem/cache/compressors/zero.hh
3 files changed, 23 insertions(+), 8 deletions(-)
Approvals:
Nikos Nikoleris: Looks good to me, approved; Looks good to me, approved
kokoro: Regressions pass
diff --git a/src/mem/cache/compressors/base.cc
b/src/mem/cache/compressors/base.cc
index de29c69..788a76f 100644
--- a/src/mem/cache/compressors/base.cc
+++ b/src/mem/cache/compressors/base.cc
@@ -153,7 +153,11 @@
// Update stats
stats.compressions++;
stats.compressionSizeBits += comp_size_bits;
- stats.compressionSize[std::ceil(std::log2(comp_size_bits))]++;
+ if (comp_size_bits != 0) {
+ stats.compressionSize[1 + std::ceil(std::log2(comp_size_bits))]++;
+ } else {
+ stats.compressionSize[0]++;
+ }
// Print debug information
DPRINTF(CacheComp, "Compressed cache line from %d to %d bits. " \
@@ -221,11 +225,15 @@
{
Stats::Group::regStats();
- compressionSize.init(std::log2(compressor.blkSize*8) + 1);
+ // Values comprised are {0, 1, 2, 4, ..., blkSize}
+ compressionSize.init(std::log2(compressor.blkSize*8) + 2);
+ compressionSize.subname(0, "0");
+ compressionSize.subdesc(0,
+ "Number of blocks that compressed to fit in 0 bits");
for (unsigned i = 0; i <= std::log2(compressor.blkSize*8); ++i) {
std::string str_i = std::to_string(1 << i);
- compressionSize.subname(i, str_i);
- compressionSize.subdesc(i,
+ compressionSize.subname(1+i, str_i);
+ compressionSize.subdesc(1+i,
"Number of blocks that compressed to fit in " + str_i + "
bits");
}
diff --git a/src/mem/cache/compressors/multi.cc
b/src/mem/cache/compressors/multi.cc
index b740a95..76ec1db 100644
--- a/src/mem/cache/compressors/multi.cc
+++ b/src/mem/cache/compressors/multi.cc
@@ -94,9 +94,16 @@
const std::size_t size = compData->getSize();
// If the compressed size is worse than the uncompressed size,
// we assume the size is the uncompressed size, and thus the
- // compression factor is 1
+ // compression factor is 1.
+ //
+ // Some compressors (notably the zero compressor) may rely on
+ // extra information being stored in the tags, or added in
+ // another compression layer. Their size can be 0, so it is
+ // assigned the highest possible compression factor (the
original
+ // block's size).
compressionFactor = (size > blk_size) ? 1 :
- alignToPowerOfTwo(std::floor(blk_size / (double) size));
+ ((size == 0) ? blk_size :
+ alignToPowerOfTwo(std::floor(blk_size / (double) size)));
}
};
struct ResultsComparator
diff --git a/src/mem/cache/compressors/zero.hh
b/src/mem/cache/compressors/zero.hh
index 57a2685..c839910 100644
--- a/src/mem/cache/compressors/zero.hh
+++ b/src/mem/cache/compressors/zero.hh
@@ -106,7 +106,7 @@
{
public:
PatternX(const DictionaryEntry bytes, const int match_location)
- : DictionaryCompressor::UncompressedPattern(X, 0, 1,
match_location,
+ : DictionaryCompressor::UncompressedPattern(X, 0, 0,
match_location,
bytes)
{
}
@@ -118,7 +118,7 @@
public:
PatternZ(const DictionaryEntry bytes, const int match_location)
: DictionaryCompressor::MaskedValuePattern<0, 0xFFFFFFFFFFFFFFFF>(
- Z, 1, 1, match_location, bytes)
+ Z, 1, 0, match_location, bytes)
{
}
};
--
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Gerrit-Project: public/gem5
Gerrit-Branch: develop
Gerrit-Change-Id: I9f7dee76576b09fdc9bef3e1f3f89be3726dcbd9
Gerrit-Change-Number: 33383
Gerrit-PatchSet: 3
Gerrit-Owner: Daniel Carvalho <[email protected]>
Gerrit-Reviewer: Daniel Carvalho <[email protected]>
Gerrit-Reviewer: Nikos Nikoleris <[email protected]>
Gerrit-Reviewer: kokoro <[email protected]>
Gerrit-MessageType: merged
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