Daniel Carvalho has submitted this change. (
https://gem5-review.googlesource.com/c/public/gem5/+/36580 )
Change subject: mem-cache: Set compression bit with its size
......................................................................
mem-cache: Set compression bit with its size
When setting the size of a compressed block, its compressibility
needs to be recalculated based on that, so move such functionality
to be done after the block has been inserted, within setSizeBits.
As a side effect, insertBlock does not need to be overridden
anymore.
Change-Id: I608f876cd2110ac5e394ffad5b29941ba458ba91
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/36580
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/compressed_tags.cc
M src/mem/cache/tags/compressed_tags.hh
M src/mem/cache/tags/super_blk.cc
4 files changed, 27 insertions(+), 53 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 09c810a..98467ab 100644
--- a/src/mem/cache/base.cc
+++ b/src/mem/cache/base.cc
@@ -853,12 +853,6 @@
CompressionBlk* compression_blk = static_cast<CompressionBlk*>(blk);
M5_VAR_USED const std::size_t prev_size =
compression_blk->getSizeBits();
- // Check if new data is co-allocatable
- const SuperBlk* superblock =
- static_cast<const SuperBlk*>(compression_blk->getSectorBlock());
- const bool is_co_allocatable =
superblock->isCompressed(compression_blk) &&
- superblock->canCoAllocate(compression_size);
-
// If compressed size didn't change enough to modify its
co-allocatability
// there is nothing to do. Otherwise we may be facing a data expansion
// (block passing from more compressed to less compressed state), or a
@@ -909,7 +903,7 @@
} else {
// If we do not move the expanded block, we must make room for
// the expansion to happen, so evict every co-allocated block
- superblock = static_cast<const SuperBlk*>(
+ const SuperBlk* superblock = static_cast<const SuperBlk*>(
compression_blk->getSectorBlock());
for (auto& sub_blk : superblock->blks) {
if (sub_blk->isValid() && (blk != sub_blk)) {
@@ -945,17 +939,6 @@
compression_blk->setSizeBits(compression_size);
compression_blk->setDecompressionLatency(decompression_lat);
- if (is_data_expansion || is_data_contraction) {
- // If contracting data, for sure data is compressed. If expanding,
- // both situations can arise. When no contraction or expansion
happens
- // block keeps its old state
- if (is_co_allocatable) {
- compression_blk->setCompressed();
- } else {
- compression_blk->setUncompressed();
- }
- }
-
return true;
}
@@ -1503,16 +1486,16 @@
return nullptr;
}
- // If using a compressor, set compression data. This must be done
before
- // block insertion, as compressed tags use this information.
+ // Insert new block at victimized entry
+ tags->insertBlock(pkt, victim);
+
+ // If using a compressor, set compression data. This must be done after
+ // insertion, as the compression bit may be set.
if (compressor) {
compressor->setSizeBits(victim, blk_size_bits);
compressor->setDecompressionLatency(victim, decompression_lat);
}
- // Insert new block at victimized entry
- tags->insertBlock(pkt, victim);
-
return victim;
}
diff --git a/src/mem/cache/tags/compressed_tags.cc
b/src/mem/cache/tags/compressed_tags.cc
index 780c738..f71deda 100644
--- a/src/mem/cache/tags/compressed_tags.cc
+++ b/src/mem/cache/tags/compressed_tags.cc
@@ -165,28 +165,6 @@
}
void
-CompressedTags::insertBlock(const PacketPtr pkt, CacheBlk *blk)
-{
- // We check if block can co-allocate before inserting, because this
check
- // assumes the block is still invalid
- CompressionBlk* compression_blk = static_cast<CompressionBlk*>(blk);
- const SuperBlk* superblock = static_cast<const SuperBlk*>(
- compression_blk->getSectorBlock());
- const bool is_co_allocatable = superblock->isCompressed() &&
- superblock->canCoAllocate(compression_blk->getSizeBits());
-
- // Insert block
- SectorTags::insertBlock(pkt, blk);
-
- // We always store compressed blocks when possible
- if (is_co_allocatable) {
- compression_blk->setCompressed();
- } else {
- compression_blk->setUncompressed();
- }
-}
-
-void
CompressedTags::forEachBlk(std::function<void(CacheBlk &)> visitor)
{
for (CompressionBlk& blk : blks) {
diff --git a/src/mem/cache/tags/compressed_tags.hh
b/src/mem/cache/tags/compressed_tags.hh
index 73231f2..306acd5 100644
--- a/src/mem/cache/tags/compressed_tags.hh
+++ b/src/mem/cache/tags/compressed_tags.hh
@@ -110,14 +110,6 @@
std::vector<CacheBlk*>& evict_blks) override;
/**
- * Insert the new block into the cache and update replacement data.
- *
- * @param pkt Packet holding the address to update
- * @param blk The block to update.
- */
- void insertBlock(const PacketPtr pkt, CacheBlk *blk) override;
-
- /**
* Visit each sub-block in the tags and apply a visitor.
*
* The visitor should be a std::function that takes a cache block.
diff --git a/src/mem/cache/tags/super_blk.cc
b/src/mem/cache/tags/super_blk.cc
index 9f7ce65..09bb207 100644
--- a/src/mem/cache/tags/super_blk.cc
+++ b/src/mem/cache/tags/super_blk.cc
@@ -93,6 +93,27 @@
CompressionBlk::setSizeBits(const std::size_t size)
{
_size = size;
+
+ SuperBlk* superblock = static_cast<SuperBlk*>(getSectorBlock());
+
+ // Either this function is called after an insertion, or an update.
+ // If somebody else is present in the block, keep the superblock's
+ // compressibility. Otherwise, check if it can co-allocate
+ const uint8_t num_valid = superblock->getNumValid();
+ assert(num_valid >= 1);
+ if (num_valid == 1) {
+ if (superblock->canCoAllocate(size)) {
+ setCompressed();
+ } else {
+ setUncompressed();
+ }
+ } else {
+ if (superblock->isCompressed(this)) {
+ setCompressed();
+ } else {
+ setUncompressed();
+ }
+ }
}
Cycles
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Gerrit-Project: public/gem5
Gerrit-Branch: develop
Gerrit-Change-Id: I608f876cd2110ac5e394ffad5b29941ba458ba91
Gerrit-Change-Number: 36580
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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