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authorZachary Amsden <zamsden@redhat.com>2010-08-19 22:07:26 -1000
committerAvi Kivity <avi@redhat.com>2010-10-24 10:51:23 +0200
commit46543ba45fc4b64ca32655efdc8d9c599b4164e2 (patch)
treea66d258a99fd7654f1fba049573d0a200ece85e6 /arch/x86
parent759379dd68c2885d1fafa433083d4487e710a685 (diff)
KVM: x86: Robust TSC compensation
Make the match of TSC find TSC writes that are close to each other instead of perfectly identical; this allows the compensator to also work in migration / suspend scenarios. Signed-off-by: Zachary Amsden <zamsden@redhat.com> Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
Diffstat (limited to 'arch/x86')
-rw-r--r--arch/x86/kvm/x86.c14
1 files changed, 10 insertions, 4 deletions
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 4bcb120cc76..4ff0c271f12 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -928,21 +928,27 @@ void kvm_write_tsc(struct kvm_vcpu *vcpu, u64 data)
struct kvm *kvm = vcpu->kvm;
u64 offset, ns, elapsed;
unsigned long flags;
+ s64 sdiff;
spin_lock_irqsave(&kvm->arch.tsc_write_lock, flags);
offset = data - native_read_tsc();
ns = get_kernel_ns();
elapsed = ns - kvm->arch.last_tsc_nsec;
+ sdiff = data - kvm->arch.last_tsc_write;
+ if (sdiff < 0)
+ sdiff = -sdiff;
/*
- * Special case: identical write to TSC within 5 seconds of
+ * Special case: close write to TSC within 5 seconds of
* another CPU is interpreted as an attempt to synchronize
- * (the 5 seconds is to accomodate host load / swapping).
+ * The 5 seconds is to accomodate host load / swapping as
+ * well as any reset of TSC during the boot process.
*
* In that case, for a reliable TSC, we can match TSC offsets,
- * or make a best guest using kernel_ns value.
+ * or make a best guest using elapsed value.
*/
- if (data == kvm->arch.last_tsc_write && elapsed < 5ULL * NSEC_PER_SEC) {
+ if (sdiff < nsec_to_cycles(5ULL * NSEC_PER_SEC) &&
+ elapsed < 5ULL * NSEC_PER_SEC) {
if (!check_tsc_unstable()) {
offset = kvm->arch.last_tsc_offset;
pr_debug("kvm: matched tsc offset for %llu\n", data);