From c2ec232920354ac1c8e07e0d2fbb8b8b314343b5 Mon Sep 17 00:00:00 2001 From: Andreas Sandberg Date: Mon, 3 Jun 2013 13:39:11 +0200 Subject: kvm: Allow architectures to override the cycle accounting mechanism Some architectures have special registers in the guest that can be used to do cycle accounting. This is generally preferrable since the prevents the guest from seeing a non-monotonic clock. This changeset adds a virtual method, getHostCycles(), that the architecture-specific code can override to implement this functionallity. The default implementation uses the hwCycles counter. --- src/cpu/kvm/base.cc | 16 ++++++++++++---- 1 file changed, 12 insertions(+), 4 deletions(-) (limited to 'src/cpu/kvm/base.cc') diff --git a/src/cpu/kvm/base.cc b/src/cpu/kvm/base.cc index b5f64664f..a0aa511ea 100644 --- a/src/cpu/kvm/base.cc +++ b/src/cpu/kvm/base.cc @@ -456,12 +456,15 @@ BaseKvmCPU::tick() } } +uint64_t +BaseKvmCPU::getHostCycles() const +{ + return hwCycles.read(); +} + Tick BaseKvmCPU::kvmRun(Tick ticks) { - uint64_t baseCycles(hwCycles.read()); - uint64_t baseInstrs(hwInstructions.read()); - // We might need to update the KVM state. syncKvmState(); // Entering into KVM implies that we'll have to reload the thread @@ -478,6 +481,11 @@ BaseKvmCPU::kvmRun(Tick ticks) DPRINTF(KvmRun, "KVM: Executing for %i ticks\n", ticks); timerOverflowed = false; + // Get hardware statistics after synchronizing contexts. The KVM + // state update might affect guest cycle counters. + uint64_t baseCycles(getHostCycles()); + uint64_t baseInstrs(hwInstructions.read()); + // Arm the run timer and start the cycle timer if it isn't // controlled by the overflow timer. Starting/stopping the cycle // timer automatically starts the other perf timers as they are in @@ -497,7 +505,7 @@ BaseKvmCPU::kvmRun(Tick ticks) hwCycles.stop(); - const uint64_t hostCyclesExecuted(hwCycles.read() - baseCycles); + const uint64_t hostCyclesExecuted(getHostCycles() - baseCycles); const uint64_t simCyclesExecuted(hostCyclesExecuted * hostFactor); const uint64_t instsExecuted(hwInstructions.read() - baseInstrs); const Tick ticksExecuted(runTimer->ticksFromHostCycles(hostCyclesExecuted)); -- cgit v1.2.3