From d0659d946be05e098883b6955d2764595997f6a4 Mon Sep 17 00:00:00 2001 From: Marcelo Tosatti Date: Tue, 16 Dec 2014 09:08:15 -0500 Subject: 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 Signed-off-by: Paolo Bonzini --- arch/x86/kvm/x86.h | 2 ++ 1 file changed, 2 insertions(+) (limited to 'arch/x86/kvm/x86.h') diff --git a/arch/x86/kvm/x86.h b/arch/x86/kvm/x86.h index cc1d61a..07994f3 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 -- cgit v1.1