diff options
| author | Marcelo Tosatti <mtosatti@redhat.com> | 2014-12-16 09:08:15 -0500 |
|---|---|---|
| committer | Paolo Bonzini <pbonzini@redhat.com> | 2015-01-08 22:47:30 +0100 |
| commit | d0659d946be05e098883b6955d2764595997f6a4 (patch) | |
| tree | 710980f2f6e1c00c8c2659f366ece12999dd0812 /arch/x86/kvm/x86.c | |
| parent | 7c6a98dfa1ba9dc64a62e73624ecea9995736bbd (diff) | |
KVM: x86: add option to advance tscdeadline hrtimer expiration
For the hrtimer which emulates the tscdeadline timer in the guest,
add an option to advance expiration, and busy spin on VM-entry waiting
for the actual expiration time to elapse.
This allows achieving low latencies in cyclictest (or any scenario
which requires strict timing regarding timer expiration).
Reduces average cyclictest latency from 12us to 8us
on Core i5 desktop.
Note: this option requires tuning to find the appropriate value
for a particular hardware/guest combination. One method is to measure the
average delay between apic_timer_fn and VM-entry.
Another method is to start with 1000ns, and increase the value
in say 500ns increments until avg cyclictest numbers stop decreasing.
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Diffstat (limited to 'arch/x86/kvm/x86.c')
| -rw-r--r-- | arch/x86/kvm/x86.c | 5 |
1 files changed, 5 insertions, 0 deletions
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index af9faed270f..559e3fd6c89 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -108,6 +108,10 @@ EXPORT_SYMBOL_GPL(kvm_max_guest_tsc_khz); static u32 tsc_tolerance_ppm = 250; module_param(tsc_tolerance_ppm, uint, S_IRUGO | S_IWUSR); +/* lapic timer advance (tscdeadline mode only) in nanoseconds */ +unsigned int lapic_timer_advance_ns = 0; +module_param(lapic_timer_advance_ns, uint, S_IRUGO | S_IWUSR); + static bool backwards_tsc_observed = false; #define KVM_NR_SHARED_MSRS 16 @@ -6312,6 +6316,7 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu) } trace_kvm_entry(vcpu->vcpu_id); + wait_lapic_expire(vcpu); kvm_x86_ops->run(vcpu); /* |