diff options
author | Nikos Nikoleris <nikos.nikoleris@arm.com> | 2019-11-26 12:59:03 +0000 |
---|---|---|
committer | Nikos Nikoleris <nikos.nikoleris@arm.com> | 2020-01-06 11:09:21 +0000 |
commit | 44e3c95555b380f62c3fa4d878d78f26ad035475 (patch) | |
tree | dae42b1608eac6b602449493a410103901d99d65 /src | |
parent | 6f864aaf4a472036e97c0ba28743f221811f1fc0 (diff) | |
download | gem5-44e3c95555b380f62c3fa4d878d78f26ad035475.tar.xz |
mem-cache: Avoid write merging if there are reads in between
This CL reworks the logic in the MSHR to make sure we do not coalesce
requests unless there is a series of write requests for the whole
cache block without any other incompatible requests (e.g., read) in
between.
Change-Id: I0b3195858fb33ef85d7aae27376506057dd53ea7
Signed-off-by: Nikos Nikoleris <nikos.nikoleris@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/23666
Reviewed-by: Daniel Carvalho <odanrc@yahoo.com.br>
Tested-by: kokoro <noreply+kokoro@google.com>
Diffstat (limited to 'src')
-rw-r--r-- | src/mem/cache/mshr.cc | 46 | ||||
-rw-r--r-- | src/mem/cache/mshr.hh | 33 |
2 files changed, 47 insertions, 32 deletions
diff --git a/src/mem/cache/mshr.cc b/src/mem/cache/mshr.cc index 4241fa375..1b21546aa 100644 --- a/src/mem/cache/mshr.cc +++ b/src/mem/cache/mshr.cc @@ -111,6 +111,52 @@ MSHR::TargetList::populateFlags() } } +void +MSHR::TargetList::updateWriteFlags(PacketPtr pkt) +{ + if (isWholeLineWrite()) { + // if we have already seen writes for the full block + // stop here, this might be a full line write followed + // by other compatible requests (e.g., reads) + return; + } + + if (canMergeWrites) { + if (!pkt->isWrite()) { + // We won't allow further merging if this hasn't + // been a write + canMergeWrites = false; + return; + } + + // Avoid merging requests with special flags (e.g., + // strictly ordered) + const Request::FlagsType no_merge_flags = + Request::UNCACHEABLE | Request::STRICT_ORDER | + Request::MMAPPED_IPR | Request::PRIVILEGED | + Request::LLSC | Request::MEM_SWAP | + Request::MEM_SWAP_COND | Request::SECURE; + const auto &req_flags = pkt->req->getFlags(); + bool compat_write = !req_flags.isSet(no_merge_flags); + + // if this is the first write, it might be a whole + // line write and even if we can't merge any + // subsequent write requests, we still need to service + // it as a whole line write (e.g., SECURE whole line + // write) + bool first_write = empty(); + if (first_write || compat_write) { + auto offset = pkt->getOffset(blkSize); + auto begin = writesBitmap.begin() + offset; + std::fill(begin, begin + pkt->getSize(), true); + } + + // We won't allow further merging if this has been a + // special write + canMergeWrites &= compat_write; + } +} + inline void MSHR::TargetList::add(PacketPtr pkt, Tick readyTime, Counter order, Target::Source source, bool markPending, diff --git a/src/mem/cache/mshr.hh b/src/mem/cache/mshr.hh index 40eb970c0..685064f39 100644 --- a/src/mem/cache/mshr.hh +++ b/src/mem/cache/mshr.hh @@ -227,38 +227,7 @@ class MSHR : public QueueEntry, public Printable * * @param pkt Packet considered for adding */ - void - updateWriteFlags(PacketPtr pkt) - { - // if we have already seen writes for the full block stop - // here, this might be a full line write followed by - // other compatible requests (e.g., reads) - if (!isWholeLineWrite()) { - // Avoid merging requests with special flags (e.g., - // strictly ordered) - const Request::FlagsType no_merge_flags = - Request::UNCACHEABLE | Request::STRICT_ORDER | - Request::MMAPPED_IPR | Request::PRIVILEGED | - Request::LLSC | Request::MEM_SWAP | - Request::MEM_SWAP_COND | Request::SECURE; - const auto &req_flags = pkt->req->getFlags(); - bool compat_write = pkt->isWrite() && - !req_flags.isSet(no_merge_flags); - canMergeWrites &= compat_write; - - // if this request is the first target in this list - // and additionally a whole-line write, we need to - // service it as a whole-line even if we won't allow - // any further merging (e.g., SECURE whole line - // write). - bool first_write = pkt->isWrite() && (size() == 0); - if (first_write || compat_write) { - auto offset = pkt->getOffset(blkSize); - auto begin = writesBitmap.begin() + offset; - std::fill(begin, begin + pkt->getSize(), true); - } - } - } + void updateWriteFlags(PacketPtr pkt); /** * Tests if the flags of this TargetList have their default |