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cpu: Fix a livelock in the o3 cpu.

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Check if an instruction just enabled interrupts and we've previously had an
interrupt pending that was not handled because interrupts were subsequently
disabled before the pipeline reached a place to handle the interrupt. In that
case squash now to make sure the interrupt is handled.
This commit is contained in:
Ali Saidi 2013-02-15 17:40:07 -05:00
parent d4eca0591d
commit b84bd3028c
2 changed files with 22 additions and 1 deletions
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6
src/cpu/o3/commit.hh
View file

@ -479,6 +479,12 @@ class DefaultCommit
/** True if last committed microop can be followed by an interrupt */
bool canHandleInterrupts;
/** Have we had an interrupt pending and then seen it de-asserted because
of a masking change? In this case the variable is set and the next time
interrupts are enabled and pending the pipeline will squash to avoid
a possible livelock senario. */
bool avoidQuiesceLiveLock;
/** Updates commit stats based on this instruction. */
void updateComInstStats(DynInstPtr &inst);

17
src/cpu/o3/commit_impl.hh
View file

@ -101,7 +101,8 @@ DefaultCommit<Impl>::DefaultCommit(O3CPU *_cpu, DerivO3CPUParams *params)
numThreads(params->numThreads),
drainPending(false),
trapLatency(params->trapLatency),
canHandleInterrupts(true)
canHandleInterrupts(true),
avoidQuiesceLiveLock(false)
{
_status = Active;
_nextStatus = Inactive;
@ -728,6 +729,7 @@ DefaultCommit<Impl>::handleInterrupt()
"it got handled. Restart fetching from the orig path.\n");
toIEW->commitInfo[0].clearInterrupt = true;
interrupt = NoFault;
avoidQuiesceLiveLock = true;
return;
}
@ -759,6 +761,7 @@ DefaultCommit<Impl>::handleInterrupt()
generateTrapEvent(0);
interrupt = NoFault;
avoidQuiesceLiveLock = false;
} else {
DPRINTF(Commit, "Interrupt pending: instruction is %sin "
"flight, ROB is %sempty\n",
@ -1058,6 +1061,18 @@ DefaultCommit<Impl>::commitInsts()
"PC skip function event, stopping commit\n");
break;
}
// Check if an instruction just enabled interrupts and we've
// previously had an interrupt pending that was not handled
// because interrupts were subsequently disabled before the
// pipeline reached a place to handle the interrupt. In that
// case squash now to make sure the interrupt is handled.
//
// If we don't do this, we might end up in a live lock situation
if (!interrupt && avoidQuiesceLiveLock &&
(!head_inst->isMicroop() || head_inst->isLastMicroop()) &&
cpu->checkInterrupts(cpu->tcBase(0)))
squashAfter(tid, head_inst);
} else {
DPRINTF(Commit, "Unable to commit head instruction PC:%s "
"[tid:%i] [sn:%i].\n",