sanchayanmaity/gem5
1
0
Fork 0
Code Issues Pull requests Packages Projects Releases Wiki Activity

O3: Keep around the last committed instruction and use for squashing.

Browse source 
Without this change 0 is always used for the youngest sequence number if
a squash occured and the ROB was empty (E.g. an instruction is marked
serializeAfter or a fetch stall prevents other instructions from issuing).
Using 0 there is a race to rename where an instruction that committed the
same cycle as the squashing instruction can have it's renamed state undone
by the squash using sequence number 0.
This commit is contained in:
Ali Saidi 2011-01-18 16:30:05 -06:00
parent ea058b14da
commit 1167ef19cf
2 changed files with 21 additions and 2 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

15
src/cpu/o3/commit.hh
View file

@ -1,4 +1,16 @@
/*
* Copyright (c) 2010 ARM Limited
* All rights reserved.
*
* The license below extends only to copyright in the software and shall
* not be construed as granting a license to any other intellectual
* property including but not limited to intellectual property relating
* to a hardware implementation of the functionality of the software
* licensed hereunder. You may use the software subject to the license
* terms below provided that you ensure that this notice is replicated
* unmodified and in its entirety in all distributions of the software,
* modified or unmodified, in source code or in binary form.
*
* Copyright (c) 2004-2006 The Regents of The University of Michigan
* All rights reserved.
*
@ -409,6 +421,9 @@ class DefaultCommit
/** The sequence number of the youngest valid instruction in the ROB. */
InstSeqNum youngestSeqNum[Impl::MaxThreads];
/** The sequence number of the last commited instruction. */
InstSeqNum lastCommitedSeqNum[Impl::MaxThreads];
/** Records if there is a trap currently in flight. */
bool trapInFlight[Impl::MaxThreads];

8
src/cpu/o3/commit_impl.hh
View file

@ -141,6 +141,7 @@ DefaultCommit<Impl>::DefaultCommit(O3CPU *_cpu, DerivO3CPUParams *params)
trapSquash[tid] = false;
tcSquash[tid] = false;
pc[tid].set(0);
lastCommitedSeqNum[tid] = 0;
}
#if FULL_SYSTEM
interrupt = NoFault;
@ -498,12 +499,12 @@ DefaultCommit<Impl>::squashAll(ThreadID tid)
// Hopefully this doesn't mess things up. Basically I want to squash
// all instructions of this thread.
InstSeqNum squashed_inst = rob->isEmpty() ?
0 : rob->readHeadInst(tid)->seqNum - 1;
lastCommitedSeqNum[tid] : rob->readHeadInst(tid)->seqNum - 1;
// All younger instructions will be squashed. Set the sequence
// number as the youngest instruction in the ROB (0 in this case.
// Hopefully nothing breaks.)
youngestSeqNum[tid] = 0;
youngestSeqNum[tid] = lastCommitedSeqNum[tid];
rob->squash(squashed_inst, tid);
changedROBNumEntries[tid] = true;
@ -960,6 +961,9 @@ DefaultCommit<Impl>::commitInsts()
TheISA::advancePC(pc[tid], head_inst->staticInst);
// Keep track of the last sequence number commited
lastCommitedSeqNum[tid] = head_inst->seqNum;
// If this is an instruction that doesn't play nicely with
// others squash everything and restart fetch
if (head_inst->isSquashAfter())