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@xxxxxxxxxx>
> ---
> 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?
Jan
--
Siemens AG, Corporate Technology, CT T DE IT 1
Corporate Competence Center Embedded Linux
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