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| author | Wanpeng Li <wanpengli@tencent.com> | 2018-05-29 09:53:17 +0300 |
|---|---|---|
| committer | Paolo Bonzini <pbonzini@redhat.com> | 2018-06-04 18:51:59 +0300 |
| commit | c5ce8235cffa00c207e24210329094d7634bb467 (patch) | |
| tree | 9bc040bb9c249aa5792c06f869a1dedb51afa0db /arch/x86 | |
| parent | 71e9d9aeec7036ece9de8e51082f94d59c31be9a (diff) | |
| download | linux-c5ce8235cffa00c207e24210329094d7634bb467.tar.xz | |
KVM: VMX: Optimize tscdeadline timer latency
'Commit d0659d946be0 ("KVM: x86: add option to advance tscdeadline
hrtimer expiration")' advances the tscdeadline (the timer is emulated
by hrtimer) expiration in order that the latency which is incurred
by hypervisor (apic_timer_fn -> vmentry) can be avoided. This patch
adds the advance tscdeadline expiration support to which the tscdeadline
timer is emulated by VMX preemption timer to reduce the hypervisor
lantency (handle_preemption_timer -> vmentry). The guest can also
set an expiration that is very small (for example in Linux if an
hrtimer feeds a expiration in the past); in that case we set delta_tsc
to 0, leading to an immediately vmexit when delta_tsc is not bigger than
advance ns.
This patch can reduce ~63% latency (~4450 cycles to ~1660 cycles on
a haswell desktop) for kvm-unit-tests/tscdeadline_latency when testing
busy waits.
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Radim Krčmář <rkrcmar@redhat.com>
Signed-off-by: Wanpeng Li <wanpengli@tencent.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Diffstat (limited to 'arch/x86')
| -rw-r--r-- | arch/x86/kvm/vmx.c | 8 | ||||
| -rw-r--r-- | arch/x86/kvm/x86.c | 1 |
2 files changed, 8 insertions, 1 deletions
diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c index d205e9246f99..aff0f3ee6a1d 100644 --- a/arch/x86/kvm/vmx.c +++ b/arch/x86/kvm/vmx.c @@ -12435,7 +12435,7 @@ static inline int u64_shl_div_u64(u64 a, unsigned int shift, static int vmx_set_hv_timer(struct kvm_vcpu *vcpu, u64 guest_deadline_tsc) { struct vcpu_vmx *vmx; - u64 tscl, guest_tscl, delta_tsc; + u64 tscl, guest_tscl, delta_tsc, lapic_timer_advance_cycles; if (kvm_mwait_in_guest(vcpu->kvm)) return -EOPNOTSUPP; @@ -12444,6 +12444,12 @@ static int vmx_set_hv_timer(struct kvm_vcpu *vcpu, u64 guest_deadline_tsc) tscl = rdtsc(); guest_tscl = kvm_read_l1_tsc(vcpu, tscl); delta_tsc = max(guest_deadline_tsc, guest_tscl) - guest_tscl; + lapic_timer_advance_cycles = nsec_to_cycles(vcpu, lapic_timer_advance_ns); + + if (delta_tsc > lapic_timer_advance_cycles) + delta_tsc -= lapic_timer_advance_cycles; + else + delta_tsc = 0; /* Convert to host delta tsc if tsc scaling is enabled */ if (vcpu->arch.tsc_scaling_ratio != kvm_default_tsc_scaling_ratio && diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 1d3dfc2c941d..93dd25d005a1 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -138,6 +138,7 @@ module_param(tsc_tolerance_ppm, uint, S_IRUGO | S_IWUSR); /* lapic timer advance (tscdeadline mode only) in nanoseconds */ unsigned int __read_mostly lapic_timer_advance_ns = 0; module_param(lapic_timer_advance_ns, uint, S_IRUGO | S_IWUSR); +EXPORT_SYMBOL_GPL(lapic_timer_advance_ns); static bool __read_mostly vector_hashing = true; module_param(vector_hashing, bool, S_IRUGO); |