Daniel Carvalho has submitted this change. (
https://gem5-review.googlesource.com/c/public/gem5/+/36579 )
Change subject: mem-cache: Add data expansion and compaction checking
functions
......................................................................
mem-cache: Add data expansion and compaction checking functions
Data expansion and compaction are determined according to the compaction
method being used. Therefore, do the verification on the blocks instead
of the cache.
Change-Id: I652418a5f4c6d5b946a9925d6287a995f262f02a
Signed-off-by: Daniel R. Carvalho <[email protected]>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/36579
Reviewed-by: Nikos Nikoleris <[email protected]>
Maintainer: Nikos Nikoleris <[email protected]>
Tested-by: kokoro <[email protected]>
---
M src/mem/cache/base.cc
M src/mem/cache/tags/super_blk.cc
M src/mem/cache/tags/super_blk.hh
3 files changed, 49 insertions(+), 9 deletions(-)
Approvals:
Nikos Nikoleris: Looks good to me, approved; Looks good to me, approved
kokoro: Regressions pass
diff --git a/src/mem/cache/base.cc b/src/mem/cache/base.cc
index 78e3f3e..09c810a 100644
--- a/src/mem/cache/base.cc
+++ b/src/mem/cache/base.cc
@@ -849,10 +849,6 @@
compressor->compress(data, compression_lat, decompression_lat);
std::size_t compression_size = comp_data->getSizeBits();
- // If block's compression factor increased, it may not be
co-allocatable
- // anymore. If so, some blocks might need to be evicted to make room
for
- // the bigger block
-
// Get previous compressed size
CompressionBlk* compression_blk = static_cast<CompressionBlk*>(blk);
M5_VAR_USED const std::size_t prev_size =
compression_blk->getSizeBits();
@@ -867,16 +863,18 @@
// there is nothing to do. Otherwise we may be facing a data expansion
// (block passing from more compressed to less compressed state), or a
// data contraction (less to more).
- const bool was_compressed = compression_blk->isCompressed();
bool is_data_expansion = false;
bool is_data_contraction = false;
+ const CompressionBlk::OverwriteType overwrite_type =
+ compression_blk->checkExpansionContraction(compression_size);
string op_name = "";
- if (was_compressed && !is_co_allocatable) {
- is_data_expansion = true;
+ if (overwrite_type == CompressionBlk::DATA_EXPANSION) {
op_name = "expansion";
- } else if (moveContractions && !was_compressed && is_co_allocatable) {
- is_data_contraction = true;
+ is_data_expansion = true;
+ } else if ((overwrite_type == CompressionBlk::DATA_CONTRACTION) &&
+ moveContractions) {
op_name = "contraction";
+ is_data_contraction = true;
}
// If block changed compression state, it was possibly co-allocated
with
diff --git a/src/mem/cache/tags/super_blk.cc
b/src/mem/cache/tags/super_blk.cc
index a6d8afb..9f7ce65 100644
--- a/src/mem/cache/tags/super_blk.cc
+++ b/src/mem/cache/tags/super_blk.cc
@@ -114,6 +114,21 @@
setUncompressed();
}
+CompressionBlk::OverwriteType
+CompressionBlk::checkExpansionContraction(const std::size_t size) const
+{
+ // @todo As of now only two states are supported: compressed to its
+ // maximum compression, and uncompressed. Support for intermediate
+ // states (e.g., if MaxCR=4, 2/4 and 3/4 of the blkSize) should be
added
+ const SuperBlk* superblock =
+ static_cast<const SuperBlk*>(getSectorBlock());
+ const bool prev_compressed = isCompressed();
+ const bool new_compressed = superblock->canCoAllocate(size);
+ return (prev_compressed == new_compressed) ? UNCHANGED :
+ ((prev_compressed & !new_compressed) ? DATA_EXPANSION :
+ DATA_CONTRACTION);
+}
+
std::string
CompressionBlk::print() const
{
diff --git a/src/mem/cache/tags/super_blk.hh
b/src/mem/cache/tags/super_blk.hh
index d7abe18..354b3f5 100644
--- a/src/mem/cache/tags/super_blk.hh
+++ b/src/mem/cache/tags/super_blk.hh
@@ -63,6 +63,21 @@
bool _compressed;
public:
+ /**
+ * When an overwrite happens, the data size may change an not fit in
its
+ * current container any longer. This enum declared which kind of size
+ * change happened in this situation.
+ */
+ enum OverwriteType : int
+ {
+ /** New data contents are considered smaller than previous
contents. */
+ DATA_CONTRACTION = -1,
+ /** New and old contents are considered of similar sizes. */
+ UNCHANGED = 0,
+ /** New data contents are considered larger than previous
contents. */
+ DATA_EXPANSION = 1,
+ };
+
CompressionBlk();
CompressionBlk(const CompressionBlk&) = delete;
CompressionBlk& operator=(const CompressionBlk&) = delete;
@@ -126,6 +141,18 @@
void invalidate() override;
/**
+ * Determines if changing the size of the block will cause a data
+ * expansion (new size is bigger) or contraction (new size is smaller).
+ * Sizes are not necessarily compared at at bit granularities (e.g., 20
+ * bits is considered equal to 23 bits when blocks use 32-bit spaces as
+ * minimum allocation units).
+ *
+ * @param size The new compressed size.
+ * @return Type of size change. @sa OverwriteType.
+ */
+ OverwriteType checkExpansionContraction(const std::size_t size) const;
+
+ /**
* Pretty-print sector offset and other CacheBlk information.
*
* @return string with basic state information
--
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Gerrit-Project: public/gem5
Gerrit-Branch: develop
Gerrit-Change-Id: I652418a5f4c6d5b946a9925d6287a995f262f02a
Gerrit-Change-Number: 36579
Gerrit-PatchSet: 4
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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