From 642a563cf08171f1a89ae67229e93187cae28bd8 Mon Sep 17 00:00:00 2001 From: Tuan Ta Date: Mon, 2 Apr 2018 15:18:57 -0400 Subject: cpu: Prevent suspended TimingSimple CPUs from fetching next instructions 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 Maintainer: Brandon Potter --- src/cpu/simple/timing.cc | 23 +++++++++++++++-------- 1 file changed, 15 insertions(+), 8 deletions(-) diff --git a/src/cpu/simple/timing.cc b/src/cpu/simple/timing.cc index 14e760af9..b5450cf5f 100644 --- a/src/cpu/simple/timing.cc +++ b/src/cpu/simple/timing.cc @@ -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(fault) ? - clockEdge(syscallRetryLatency) : clockEdge(); - - reschedule(fetchEvent, stall, true); + // 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"); + + Tick stall = dynamic_pointer_cast(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 -- cgit v1.2.3