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cpu: Fix o3 drain bug

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For X86, the o3 CPU would get stuck with the commit stage not being
drained if an interrupt arrived while drain was pending. isDrained()
makes sure that pcState.microPC() == 0, thus ensuring that we are at
an instruction boundary. However, when we take an interrupt we
execute:

    pcState.upc(romMicroPC(entry));
    pcState.nupc(romMicroPC(entry) + 1);
    tc->pcState(pcState);

As a result, the MicroPC is no longer zero. This patch ensures the drain is
delayed until no interrupts are present.  Once draining, non-synchronous
interrupts are deffered until after the switch.
This commit is contained in:
Mitch Hayenga 2014-09-03 07:42:45 -04:00
parent bb1e6cf7c4
commit 659bdc1a6b
2 changed files with 22 additions and 4 deletions
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11
src/cpu/o3/commit.hh
View file

@ -438,9 +438,18 @@ class DefaultCommit
/** Number of Active Threads */
ThreadID numThreads;
/** Is a drain pending. */
/** Is a drain pending? Commit is looking for an instruction boundary while
* there are no pending interrupts
*/
bool drainPending;
/** Is a drain imminent? Commit has found an instruction boundary while no
* interrupts were present or in flight. This was the last architecturally
* committed instruction. Interrupts disabled and pipeline flushed.
* Waiting for structures to finish draining.
*/
bool drainImminent;
/** The latency to handle a trap. Used when scheduling trap
* squash event.
*/

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

@ -104,6 +104,7 @@ DefaultCommit<Impl>::DefaultCommit(O3CPU *_cpu, DerivO3CPUParams *params)
commitWidth(params->commitWidth),
numThreads(params->numThreads),
drainPending(false),
drainImminent(false),
trapLatency(params->trapLatency),
canHandleInterrupts(true),
avoidQuiesceLiveLock(false)
@ -406,6 +407,7 @@ void
DefaultCommit<Impl>::drainResume()
{
drainPending = false;
drainImminent = false;
}
template <class Impl>
@ -816,8 +818,10 @@ template <class Impl>
void
DefaultCommit<Impl>::propagateInterrupt()
{
// Don't propagate intterupts if we are currently handling a trap or
// in draining and the last observable instruction has been committed.
if (commitStatus[0] == TrapPending || interrupt || trapSquash[0] ||
tcSquash[0])
tcSquash[0] || drainImminent)
return;
// Process interrupts if interrupts are enabled, not in PAL
@ -1089,10 +1093,15 @@ DefaultCommit<Impl>::commitInsts()
squashAfter(tid, head_inst);
if (drainPending) {
DPRINTF(Drain, "Draining: %i:%s\n", tid, pc[tid]);
if (pc[tid].microPC() == 0 && interrupt == NoFault) {
if (pc[tid].microPC() == 0 && interrupt == NoFault &&
!thread[tid]->trapPending) {
// Last architectually committed instruction.
// Squash the pipeline, stall fetch, and use
// drainImminent to disable interrupts
DPRINTF(Drain, "Draining: %i:%s\n", tid, pc[tid]);
squashAfter(tid, head_inst);
cpu->commitDrained(tid);
drainImminent = true;
}
}