| Message ID | 1539046928-18600-1-git-send-email-wanpengli@tencent.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [v2] KVM: LAPIC: Tune lapic_timer_advance_ns automatically | expand |
On 09/10/2018 03:02, Wanpeng Li wrote: > From: Wanpeng Li <wanpengli@tencent.com> > > In cloud environment, lapic_timer_advance_ns is needed to be tuned for every CPU > generations, and every host kernel versions(the kvm-unit-tests/tscdeadline_latency.flat > is 5700 cycles for upstream kernel and 9600 cycles for our 3.10 product kernel, > both preemption_timer=N, Skylake server). > > This patch adds the capability to automatically tune lapic_timer_advance_ns > step by step, the initial value is 1000ns as 'commit d0659d946be0 ("KVM: x86: > add option to advance tscdeadline hrtimer expiration")' recommended, it will be > reduced when it is too early, and increased when it is too late. The guest_tsc > and tsc_deadline are hard to equal, so we assume we are done when the delta > is within a small scope e.g. 100 cycles. This patch reduces latency > (kvm-unit-tests/tscdeadline_latency, busy waits, preemption_timer enabled) > from ~2600 cyles to ~1200 cyles on our Skylake server. > > Cc: Paolo Bonzini <pbonzini@redhat.com> > Cc: Radim Krčmář <rkrcmar@redhat.com> > Cc: Liran Alon <liran.alon@oracle.com> > Signed-off-by: Wanpeng Li <wanpengli@tencent.com> > --- > v1 -> v2: > * converts between guest TSC units to host nanoseconds correctly > * put hard-coded numbers to #define > > arch/x86/kvm/lapic.c | 25 ++++++++++++++++++++++++- > arch/x86/kvm/x86.c | 2 +- > 2 files changed, 25 insertions(+), 2 deletions(-) > > diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c > index fbb0e6d..197cf5d 100644 > --- a/arch/x86/kvm/lapic.c > +++ b/arch/x86/kvm/lapic.c > @@ -70,6 +70,11 @@ > #define APIC_BROADCAST 0xFF > #define X2APIC_BROADCAST 0xFFFFFFFFul > > +static bool lapic_timer_advance_adjust_done = false; > +#define LAPIC_TIMER_ADVANCE_ADJUST_DONE 100 > +/* step-by-step approximation to mitigate fluctuation */ > +#define LAPIC_TIMER_ADVANCE_ADJUST_STEP 8 > + > static inline int apic_test_vector(int vec, void *bitmap) > { > return test_bit(VEC_POS(vec), (bitmap) + REG_POS(vec)); > @@ -1472,7 +1477,7 @@ static bool lapic_timer_int_injected(struct kvm_vcpu *vcpu) > void wait_lapic_expire(struct kvm_vcpu *vcpu) > { > struct kvm_lapic *apic = vcpu->arch.apic; > - u64 guest_tsc, tsc_deadline; > + u64 guest_tsc, tsc_deadline, ns; > > if (!lapic_in_kernel(vcpu)) > return; > @@ -1492,6 +1497,24 @@ void wait_lapic_expire(struct kvm_vcpu *vcpu) > if (guest_tsc < tsc_deadline) > __delay(min(tsc_deadline - guest_tsc, > nsec_to_cycles(vcpu, lapic_timer_advance_ns))); > + > + if (!lapic_timer_advance_adjust_done) { > + /* too early */ > + if (guest_tsc < tsc_deadline) { > + ns = (tsc_deadline - guest_tsc) * 1000000ULL; > + do_div(ns, vcpu->arch.virtual_tsc_khz); > + lapic_timer_advance_ns -= min((unsigned int)ns, > + lapic_timer_advance_ns / LAPIC_TIMER_ADVANCE_ADJUST_STEP); > + } else { > + /* too late */ > + ns = (guest_tsc - tsc_deadline) * 1000000ULL; > + do_div(ns, vcpu->arch.virtual_tsc_khz); > + lapic_timer_advance_ns += min((unsigned int)ns, > + lapic_timer_advance_ns / LAPIC_TIMER_ADVANCE_ADJUST_STEP); > + } > + if (abs(guest_tsc - tsc_deadline) < LAPIC_TIMER_ADVANCE_ADJUST_DONE) > + lapic_timer_advance_adjust_done = true; > + } > } > > static void start_sw_tscdeadline(struct kvm_lapic *apic) > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c > index ca71773..1f3f955 100644 > --- a/arch/x86/kvm/x86.c > +++ b/arch/x86/kvm/x86.c > @@ -136,7 +136,7 @@ static u32 __read_mostly tsc_tolerance_ppm = 250; > 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; > +unsigned int __read_mostly lapic_timer_advance_ns = 1000; > module_param(lapic_timer_advance_ns, uint, S_IRUGO | S_IWUSR); > EXPORT_SYMBOL_GPL(lapic_timer_advance_ns); > > Queued, thanks. Paolo
diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c index fbb0e6d..197cf5d 100644 --- a/arch/x86/kvm/lapic.c +++ b/arch/x86/kvm/lapic.c @@ -70,6 +70,11 @@ #define APIC_BROADCAST 0xFF #define X2APIC_BROADCAST 0xFFFFFFFFul +static bool lapic_timer_advance_adjust_done = false; +#define LAPIC_TIMER_ADVANCE_ADJUST_DONE 100 +/* step-by-step approximation to mitigate fluctuation */ +#define LAPIC_TIMER_ADVANCE_ADJUST_STEP 8 + static inline int apic_test_vector(int vec, void *bitmap) { return test_bit(VEC_POS(vec), (bitmap) + REG_POS(vec)); @@ -1472,7 +1477,7 @@ static bool lapic_timer_int_injected(struct kvm_vcpu *vcpu) void wait_lapic_expire(struct kvm_vcpu *vcpu) { struct kvm_lapic *apic = vcpu->arch.apic; - u64 guest_tsc, tsc_deadline; + u64 guest_tsc, tsc_deadline, ns; if (!lapic_in_kernel(vcpu)) return; @@ -1492,6 +1497,24 @@ void wait_lapic_expire(struct kvm_vcpu *vcpu) if (guest_tsc < tsc_deadline) __delay(min(tsc_deadline - guest_tsc, nsec_to_cycles(vcpu, lapic_timer_advance_ns))); + + if (!lapic_timer_advance_adjust_done) { + /* too early */ + if (guest_tsc < tsc_deadline) { + ns = (tsc_deadline - guest_tsc) * 1000000ULL; + do_div(ns, vcpu->arch.virtual_tsc_khz); + lapic_timer_advance_ns -= min((unsigned int)ns, + lapic_timer_advance_ns / LAPIC_TIMER_ADVANCE_ADJUST_STEP); + } else { + /* too late */ + ns = (guest_tsc - tsc_deadline) * 1000000ULL; + do_div(ns, vcpu->arch.virtual_tsc_khz); + lapic_timer_advance_ns += min((unsigned int)ns, + lapic_timer_advance_ns / LAPIC_TIMER_ADVANCE_ADJUST_STEP); + } + if (abs(guest_tsc - tsc_deadline) < LAPIC_TIMER_ADVANCE_ADJUST_DONE) + lapic_timer_advance_adjust_done = true; + } } static void start_sw_tscdeadline(struct kvm_lapic *apic) diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index ca71773..1f3f955 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -136,7 +136,7 @@ static u32 __read_mostly tsc_tolerance_ppm = 250; 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; +unsigned int __read_mostly lapic_timer_advance_ns = 1000; module_param(lapic_timer_advance_ns, uint, S_IRUGO | S_IWUSR); EXPORT_SYMBOL_GPL(lapic_timer_advance_ns);