From: David Woodhouse <[email protected]> Eliminate three sources of unnecessary KVM_REQ_GLOBAL_CLOCK_UPDATE:
1. kvm_write_system_time(): The global clock update was a workaround for ever-drifting clocks based on the host's CLOCK_MONOTONIC subject to NTP skew. On booting or resuming a guest, it just leads to running kvm_guest_time_update() twice for each vCPU for no good reason. Use KVM_REQ_CLOCK_UPDATE on the vCPU itself, and only when the clock is being enabled, not disabled. 2. kvm_arch_vcpu_load(): Use KVM_REQ_CLOCK_UPDATE instead of KVM_REQ_GLOBAL_CLOCK_UPDATE. There is no need to update all vCPUs' clocks when one vCPU is loaded. 3. kvm_gen_kvmclock_update(): Skip the periodic global update entirely when in master clock mode, since the clock is defined precisely by the guest TSC and doesn't drift. Signed-off-by: David Woodhouse <[email protected]> Reviewed-by: Paul Durrant <[email protected]> --- arch/x86/kvm/x86.c | 12 ++++++++---- 1 file changed, 8 insertions(+), 4 deletions(-) diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 0656d901fe79..7d9ec0638d28 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -2457,13 +2457,13 @@ static void kvm_write_system_time(struct kvm_vcpu *vcpu, gpa_t system_time, } vcpu->arch.time = system_time; - kvm_make_request(KVM_REQ_GLOBAL_CLOCK_UPDATE, vcpu); /* we verify if the enable bit is set... */ - if (system_time & 1) + if (system_time & 1) { kvm_gpc_activate(&vcpu->arch.pv_time, system_time & ~1ULL, sizeof(struct pvclock_vcpu_time_info)); - else + kvm_make_request(KVM_REQ_CLOCK_UPDATE, vcpu); + } else kvm_gpc_deactivate(&vcpu->arch.pv_time); return; @@ -3638,6 +3638,10 @@ static void kvm_gen_kvmclock_update(struct kvm_vcpu *v) struct kvm_vcpu *vcpu; struct kvm *kvm = v->kvm; + /* In master clock mode, the clock doesn't need periodic updates. */ + if (kvm->arch.use_master_clock) + return; + kvm_for_each_vcpu(i, vcpu, kvm) { kvm_make_request(KVM_REQ_CLOCK_UPDATE, vcpu); kvm_vcpu_kick(vcpu); @@ -5339,7 +5343,7 @@ 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_GLOBAL_CLOCK_UPDATE, vcpu); + kvm_make_request(KVM_REQ_CLOCK_UPDATE, vcpu); if (vcpu->cpu != cpu) kvm_make_request(KVM_REQ_MIGRATE_TIMER, vcpu); vcpu->cpu = cpu; -- 2.51.0
