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mem-ruby: fix CHI snoops clearing WU data

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When just forwarding a WU request, the controller waits until the WU is
acked from downstream before sending the ack upstream. This
prevents snoops clearing valid WU data.

JIRA: https://gem5.atlassian.net/browse/GEM5-1195

This was more likely to happen with shared exclusive caches, e.g:
assume core C1 and C2 with private L1/L2 and a shared exclusive L3.
C1 has as dirty copy of the line while C2 issues a WriteUnique request
to that line. The line state is RU in the L3, so the L3 will just
forward the request to the HNF, so:
- C2 issues WU to L3 cache
- L3 acks the WU, allowing C2 to send the data, while concurrently
  forwarding the WU to the HNF.
- L3 receives data from C2
- HNF sends invalidating snoops upstream because line is RU
- The snoop hazards with the pending WU at the L3 and invalidates
  the data previously received. This causes an assertion to fail when
  we resume handling the WU.

Change-Id: I51e457e0bdb648c0fff3f702b7d2c95dcf431dc5
Signed-off-by: Tiago Mück <tiago.muck@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/59990
Tested-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Jason Lowe-Power <power.jg@gmail.com>
Maintainer: Jason Lowe-Power <power.jg@gmail.com>
This commit is contained in:
Tiago Mück
2022-05-16 17:50:18 -05:00
committed by Tiago Muck
parent 1dfd319d98
commit 612f242359
1 changed files with 3 additions and 10 deletions
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13
src/mem/ruby/protocol/chi/CHI-cache-actions.sm
View File

@@ -842,16 +842,9 @@ action(Initiate_WriteUnique_PartialWrite, desc="") {
}
action(Initiate_WriteUnique_Forward, desc="") {
if (comp_wu) {
tbe.actions.push(Event:SendDBIDResp_WU);
tbe.actions.pushNB(Event:WriteFEPipe);
tbe.actions.pushNB(Event:SendWriteUnique);
tbe.actions.pushNB(Event:SendComp_WU);
} else {
tbe.actions.push(Event:SendCompDBIDResp_WU);
tbe.actions.pushNB(Event:WriteFEPipe);
tbe.actions.pushNB(Event:SendWriteUnique);
}
tbe.actions.push(Event:WriteFEPipe);
tbe.actions.push(Event:SendWriteUnique);
tbe.actions.push(Event:SendCompDBIDResp_WU);
tbe.actions.push(Event:WriteBEPipe);
tbe.actions.push(Event:SendWUData);
tbe.dataToBeInvalid := true;