Messages in this thread | | | Date | Tue, 14 Sep 2010 11:27:15 +0200 | From | Avi Kivity <> | Subject | Re: [KVM timekeeping 10/35] Fix deep C-state TSC desynchronization |
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On 09/14/2010 11:10 AM, Jan Kiszka wrote: > Am 20.08.2010 10:07, Zachary Amsden wrote: >> When CPUs with unstable TSCs enter deep C-state, TSC may stop >> running. This causes us to require resynchronization. Since >> we can't tell when this may potentially happen, we assume the >> worst by forcing re-compensation for it at every point the VCPU >> task is descheduled. >> >> Signed-off-by: Zachary Amsden<zamsden@redhat.com> >> --- >> arch/x86/kvm/x86.c | 2 +- >> 1 files changed, 1 insertions(+), 1 deletions(-) >> >> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c >> index 7fc4a55..52b6c21 100644 >> --- a/arch/x86/kvm/x86.c >> +++ b/arch/x86/kvm/x86.c >> @@ -1866,7 +1866,7 @@ void kvm_arch_vcpu_load(struct kvm_vcpu *vcpu, int cpu) >> } >> >> kvm_x86_ops->vcpu_load(vcpu, cpu); >> - if (unlikely(vcpu->cpu != cpu)) { >> + if (unlikely(vcpu->cpu != cpu) || check_tsc_unstable()) { >> /* Make sure TSC doesn't go backwards */ >> s64 tsc_delta = !vcpu->arch.last_host_tsc ? 0 : >> native_read_tsc() - vcpu->arch.last_host_tsc; > For yet unknown reason, this commit breaks Linux guests here if they are > started with only a single VCPU. They hang during boot, obviously no > longer receiving interrupts. > > I'm using kvm-kmod against a 2.6.34 host kernel, so this may be a side > effect of the wrapping, though I cannot imagine how. > > Anyone any ideas? > >
Most likely, time went backwards, and some 'future - past' calculation resulted in a negative sleep value which was then interpreted as unsigned and resulted in a 2342525634 year sleep.
Does your guest use kvmclock, tsc, or some other time source?
-- error compiling committee.c: too many arguments to function
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