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cpu: Prevent suspended TimingSimple CPUs from fetching next instructions

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In TimingSimpleCPU model, when a CPU is suspended by a syscall (e.g.,
futex(FUTEX_WAIT)), the CPU waits for another CPU to wake it up
(e.g., FUTEX_WAKE operation). While staying Idle, the suspended CPU
should not try to fetch next instructions after the syscall.

This patch added a status check before a CPU schedule a fetch event
after a fault is handled.

Change-Id: I0cc953135686c9b35afe94942aa1d0b245ec60a2
Reviewed-on: https://gem5-review.googlesource.com/8181
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Maintainer: Brandon Potter <Brandon.Potter@amd.com>
This commit is contained in:
Tuan Ta
2018-04-02 15:18:57 -04:00
parent 7341f14f14
commit 642a563cf0
1 changed files with 14 additions and 7 deletions
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21
src/cpu/simple/timing.cc
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@@ -680,25 +680,32 @@ TimingSimpleCPU::advanceInst(const Fault &fault)
return;
if (fault != NoFault) {
DPRINTF(SimpleCPU, "Fault occured, scheduling fetch event\n");
DPRINTF(SimpleCPU, "Fault occured. Handling the fault\n");
advancePC(fault);
Tick stall = dynamic_pointer_cast<SyscallRetryFault>(fault) ?
clockEdge(syscallRetryLatency) : clockEdge();
// A syscall fault could suspend this CPU (e.g., futex_wait)
// If the _status is not Idle, schedule an event to fetch the next
// instruction after 'stall' ticks.
// If the cpu has been suspended (i.e., _status == Idle), another
// cpu will wake this cpu up later.
if (_status != Idle) {
DPRINTF(SimpleCPU, "Scheduling fetch event after the Fault\n");
reschedule(fetchEvent, stall, true);
Tick stall = dynamic_pointer_cast<SyscallRetryFault>(fault) ?
clockEdge(syscallRetryLatency) : clockEdge();
reschedule(fetchEvent, stall, true);
_status = Faulting;
}
_status = Faulting;
return;
}
if (!t_info.stayAtPC)
advancePC(fault);
if (tryCompleteDrain())
return;
return;
if (_status == BaseSimpleCPU::Running) {
// kick off fetch of next instruction... callback from icache