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<zams...@redhat.com>
---
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).
Zach
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