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| author | Marcelo Tosatti <mtosatti@redhat.com> | 2013-05-09 20:21:41 -0300 |
|---|---|---|
| committer | Gleb Natapov <gleb@redhat.com> | 2013-05-15 20:36:09 +0300 |
| commit | 0061d53daf26ff713ab43ab84ae5c44b5edbefa9 (patch) | |
| tree | c9b86974498fb39210c355171c01afbae513bb59 /arch/x86/kvm/x86.c | |
| parent | f1ed0450a5fac7067590317cbf027f566b6ccbca (diff) | |
| download | lwn-0061d53daf26ff713ab43ab84ae5c44b5edbefa9.tar.gz lwn-0061d53daf26ff713ab43ab84ae5c44b5edbefa9.zip | |
KVM: x86: limit difference between kvmclock updates
kvmclock updates which are isolated to a given vcpu, such as vcpu->cpu
migration, should not allow system_timestamp from the rest of the vcpus
to remain static. Otherwise ntp frequency correction applies to one
vcpu's system_timestamp but not the others.
So in those cases, request a kvmclock update for all vcpus. The worst
case for a remote vcpu to update its kvmclock is then bounded by maximum
nohz sleep latency.
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: Gleb Natapov <gleb@redhat.com>
Diffstat (limited to 'arch/x86/kvm/x86.c')
| -rw-r--r-- | arch/x86/kvm/x86.c | 30 |
1 files changed, 28 insertions, 2 deletions
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 094b5d96ab14..8d28810a5f88 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -1588,6 +1588,30 @@ static int kvm_guest_time_update(struct kvm_vcpu *v) return 0; } +/* + * kvmclock updates which are isolated to a given vcpu, such as + * vcpu->cpu migration, should not allow system_timestamp from + * the rest of the vcpus to remain static. Otherwise ntp frequency + * correction applies to one vcpu's system_timestamp but not + * the others. + * + * So in those cases, request a kvmclock update for all vcpus. + * The worst case for a remote vcpu to update its kvmclock + * is then bounded by maximum nohz sleep latency. + */ + +static void kvm_gen_kvmclock_update(struct kvm_vcpu *v) +{ + int i; + struct kvm *kvm = v->kvm; + struct kvm_vcpu *vcpu; + + kvm_for_each_vcpu(i, vcpu, kvm) { + set_bit(KVM_REQ_CLOCK_UPDATE, &vcpu->requests); + kvm_vcpu_kick(vcpu); + } +} + static bool msr_mtrr_valid(unsigned msr) { switch (msr) { @@ -1985,7 +2009,7 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info) kvmclock_reset(vcpu); vcpu->arch.time = data; - kvm_make_request(KVM_REQ_CLOCK_UPDATE, vcpu); + kvm_make_request(KVM_REQ_GLOBAL_CLOCK_UPDATE, vcpu); /* we verify if the enable bit is set... */ if (!(data & 1)) @@ -2702,7 +2726,7 @@ void kvm_arch_vcpu_load(struct kvm_vcpu *vcpu, int cpu) * kvmclock on vcpu->cpu migration */ if (!vcpu->kvm->arch.use_master_clock || vcpu->cpu == -1) - kvm_make_request(KVM_REQ_CLOCK_UPDATE, vcpu); + kvm_make_request(KVM_REQ_GLOBAL_CLOCK_UPDATE, vcpu); if (vcpu->cpu != cpu) kvm_migrate_timers(vcpu); vcpu->cpu = cpu; @@ -5703,6 +5727,8 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu) __kvm_migrate_timers(vcpu); if (kvm_check_request(KVM_REQ_MASTERCLOCK_UPDATE, vcpu)) kvm_gen_update_masterclock(vcpu->kvm); + if (kvm_check_request(KVM_REQ_GLOBAL_CLOCK_UPDATE, vcpu)) + kvm_gen_kvmclock_update(vcpu); if (kvm_check_request(KVM_REQ_CLOCK_UPDATE, vcpu)) { r = kvm_guest_time_update(vcpu); if (unlikely(r)) |