lkml.org 
[lkml]   [2010]   [Jun]   [16]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: [PATCH 04/17] Fix deep C-state TSC desynchronization
    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.
    >
    >
    Is there any method to do the compensation on host TSC when recovering
    from C-state? It should be simpler than do it on guest TSC.
    > Signed-off-by: Zachary Amsden <zamsden@redhat.com>
    > ---
    > arch/x86/kvm/x86.c | 11 +++++++++++
    > 1 files changed, 11 insertions(+), 0 deletions(-)
    >
    > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
    > index c8289d0..618c435 100644
    > --- a/arch/x86/kvm/x86.c
    > +++ b/arch/x86/kvm/x86.c
    > @@ -1822,7 +1822,18 @@ void kvm_arch_vcpu_put(struct kvm_vcpu *vcpu)
    > {
    > kvm_x86_ops->vcpu_put(vcpu);
    > kvm_put_guest_fpu(vcpu);
    > +
    > vcpu->arch.last_host_tsc = native_read_tsc();
    > +
    > + /*
    > + * When potentially leaving a CPU with unstable TSCs, we risk
    > + * that the CPU enters deep C-state. If it does, the TSC may
    > + * go out of sync but we will not recalibrate because the test
    > + * vcpu->cpu != cpu can not detect this condition. So set
    > + * vcpu->cpu = -1 to force the recalibration above.
    > + */
    > + if (check_tsc_unstable())
    > + vcpu->cpu = -1;
    > }
    >
    > static int is_efer_nx(void)
    >



    \
     
     \ /
      Last update: 2010-06-16 10:07    [W:0.025 / U:2.364 seconds]
    ©2003-2016 Jasper Spaans. hosted at Digital OceanAdvertise on this site