mem-ruby: fix inconsistent WBs for dirty data

Initiate_MaitainCoherence would not trigger a writeback if
tbe.dataMaybeDirtyUpstream is set due to the assumption that
the upstream cache would writeback any dirty data. However this
is not the case if we use this action finalize a CleanUnique, e.g.:

- L1-A has data in SC
- L1-B has data in SD
- L2 has data in RUSD (L2 is an exclusive cache)
- L1-A sends CleanUnique to L2
- L2 invalidates L1-B and receives dirty data.
- L2 acks the CleanUnique; L1-A is now UC
- L2 has the dirty data but drops it because dataMaybeDirtyUpstream
- L1-A doesn't modify the data and eventually evicts it with WriteEvict
- Data from WriteEvicts are dropped at the HNF and we lose the line

This patch removes the tbe.dataMaybeDirtyUpstream check.
Instead it only skips the WriteBack if an upstream cache is in
SD state, when it's guaranteed it will writeback the dirty data.


Change-Id: I6722bc25068b0c44afcf261abc8824f1d80c09f9
Signed-off-by: Tiago Mück <>
Tested-by: kokoro <>
Reviewed-by: Daecheol You <>
Reviewed-by: Jason Lowe-Power <>
Maintainer: Jason Lowe-Power <>
1 file changed