On 06/16/2010 03:52 AM, Glauber Costa wrote:
On Mon, Jun 14, 2010 at 09:34:18PM -1000, Zachary Amsden wrote:Attempt to synchronize TSCs which are reset to the same value. In the case of a reliable hardware TSC, we can just re-use the same offset, but on non-reliable hardware, we can get closer by adjusting the offset to match the elapsed time. Signed-off-by: Zachary Amsden<zamsden@xxxxxxxxxx> --- arch/x86/kvm/x86.c | 34 ++++++++++++++++++++++++++++++++-- 1 files changed, 32 insertions(+), 2 deletions(-) diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 8e836e9..cedb71f 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -937,14 +937,44 @@ static inline void kvm_request_guest_time_update(struct kvm_vcpu *v) set_bit(KVM_REQ_CLOCK_SYNC,&v->requests); } +static inline int kvm_tsc_reliable(void) +{ + return (boot_cpu_has(X86_FEATURE_CONSTANT_TSC)&& + boot_cpu_has(X86_FEATURE_NONSTOP_TSC)&& + !check_tsc_unstable()); +} +why can't we re-use vmware TSC_RELIABLE flag?
It's only set for VMware. Basically, it means "you are running in a VMware hypervisor, TSC is reliable". Which KVM won't ever be, at least, not in production use, so it doesn't make that sort of sense here. Besides, a system with a reliable TSC can become a system without a reliable TSC : CPU hotplug will always guarantee this.
We could, however, have the guest set the TSC_RELIABLE flag for itself if KVM somehow makes that promise (currently, it does not).
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