diff options
| author | Marcelo Tosatti <mtosatti@redhat.com> | 2014-12-16 17:08:15 +0300 |
|---|---|---|
| committer | Paolo Bonzini <pbonzini@redhat.com> | 2015-01-09 00:47:30 +0300 |
| commit | d0659d946be05e098883b6955d2764595997f6a4 (patch) | |
| tree | 710980f2f6e1c00c8c2659f366ece12999dd0812 /arch/x86/kvm/x86.h | |
| parent | 7c6a98dfa1ba9dc64a62e73624ecea9995736bbd (diff) | |
| download | linux-d0659d946be05e098883b6955d2764595997f6a4.tar.xz | |
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.h')
| -rw-r--r-- | arch/x86/kvm/x86.h | 2 |
1 files changed, 2 insertions, 0 deletions
diff --git a/arch/x86/kvm/x86.h b/arch/x86/kvm/x86.h index cc1d61af6140..07994f38dacf 100644 --- a/arch/x86/kvm/x86.h +++ b/arch/x86/kvm/x86.h @@ -170,5 +170,7 @@ extern u64 kvm_supported_xcr0(void); extern unsigned int min_timer_period_us; +extern unsigned int lapic_timer_advance_ns; + extern struct static_key kvm_no_apic_vcpu; #endif |