tree 1b7e48d5116ecbc8255c7006b7fbabcf63707497
parent abd33d6fd26bb69d3bf53ceb6c2dc8f90d893e34
author Tiago Muck <tiago.muck@arm.com> 1549561016 -0600
committer Tiago Mück <tiago.muck@arm.com> 1557871272 +0000

mem-ruby: Prevent response stalls on MOESI_CMP_directory

When a message triggers a transition that has actions which allocate
TBEs, the generated code automatically includes a check for the TBETable
size before executing any action. If the table is full, the transition
returns TransitionResult_ResourceStall and no more messages from the
buffer are handled (until the next cycle).

This behavior may lead to deadlocks in the MOESI_CMP_directory protocol
since events triggered by the response queue may allocate TBEs (e.g.
L2 replacements triggered by the response queue). If the table is full,
the queue is stalled preventing other responses from freeing TBEs.

This patch fixes this by handling WRITEBACK_DIRTY_DATA/CLEAN_DATA messages
as requests and WB_ACK/WB_NACK as responses. All controllers are changed
to work with the new types. With this fix, responses are always
handled first in all controllers, and no response triggers TBE
allocations.

Change-Id: I377c0ec4f06d528e9f0541daf3dcc621184f2524
Signed-off-by: Tiago Muck <tiago.muck@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/18408
Tested-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Matthew Poremba <matthew.poremba@amd.com>
Reviewed-by: Nikos Nikoleris <nikos.nikoleris@arm.com>
Reviewed-by: John Alsop <johnathan.alsop@amd.com>
Maintainer: Jason Lowe-Power <jason@lowepower.com>