* [PATCH] KVM: LAPIC: Tune lapic_timer_advance_ns automatically @ 2018-09-28 6:12 Wanpeng Li 2018-10-01 14:00 ` Paolo Bonzini 2018-10-07 21:02 ` Liran Alon 0 siblings, 2 replies; 6+ messages in thread From: Wanpeng Li @ 2018-09-28 6:12 UTC (permalink / raw) To: linux-kernel, kvm; +Cc: Paolo Bonzini, Radim Krčmář 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 d0659d946be05 (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> Signed-off-by: Wanpeng Li <wanpengli@tencent.com> --- arch/x86/kvm/lapic.c | 7 +++++++ arch/x86/kvm/x86.c | 2 +- 2 files changed, 8 insertions(+), 1 deletion(-) diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c index fbb0e6d..b756f12 100644 --- a/arch/x86/kvm/lapic.c +++ b/arch/x86/kvm/lapic.c @@ -70,6 +70,8 @@ #define APIC_BROADCAST 0xFF #define X2APIC_BROADCAST 0xFFFFFFFFul +static bool __read_mostly lapic_timer_advance_adjust_done = false; + static inline int apic_test_vector(int vec, void *bitmap) { return test_bit(VEC_POS(vec), (bitmap) + REG_POS(vec)); @@ -1492,6 +1494,11 @@ 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) { + lapic_timer_advance_ns += (s64)(guest_tsc - tsc_deadline) / 8; + if (abs(guest_tsc - tsc_deadline) < 100) + 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 edbf00e..e865d12 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 lapic_timer_advance_ns = 1000; module_param(lapic_timer_advance_ns, uint, S_IRUGO | S_IWUSR); EXPORT_SYMBOL_GPL(lapic_timer_advance_ns); -- 2.7.4 ^ permalink raw reply related [flat|nested] 6+ messages in thread
* Re: [PATCH] KVM: LAPIC: Tune lapic_timer_advance_ns automatically 2018-09-28 6:12 [PATCH] KVM: LAPIC: Tune lapic_timer_advance_ns automatically Wanpeng Li @ 2018-10-01 14:00 ` Paolo Bonzini 2018-10-07 21:02 ` Liran Alon 1 sibling, 0 replies; 6+ messages in thread From: Paolo Bonzini @ 2018-10-01 14:00 UTC (permalink / raw) To: Wanpeng Li, linux-kernel, kvm; +Cc: Radim Krčmář On 28/09/2018 08:12, 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 d0659d946be05 (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> > Signed-off-by: Wanpeng Li <wanpengli@tencent.com> > --- > arch/x86/kvm/lapic.c | 7 +++++++ > arch/x86/kvm/x86.c | 2 +- > 2 files changed, 8 insertions(+), 1 deletion(-) > > diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c > index fbb0e6d..b756f12 100644 > --- a/arch/x86/kvm/lapic.c > +++ b/arch/x86/kvm/lapic.c > @@ -70,6 +70,8 @@ > #define APIC_BROADCAST 0xFF > #define X2APIC_BROADCAST 0xFFFFFFFFul > > +static bool __read_mostly lapic_timer_advance_adjust_done = false; > + > static inline int apic_test_vector(int vec, void *bitmap) > { > return test_bit(VEC_POS(vec), (bitmap) + REG_POS(vec)); > @@ -1492,6 +1494,11 @@ 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) { > + lapic_timer_advance_ns += (s64)(guest_tsc - tsc_deadline) / 8; > + if (abs(guest_tsc - tsc_deadline) < 100) > + 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 edbf00e..e865d12 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 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 ^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH] KVM: LAPIC: Tune lapic_timer_advance_ns automatically 2018-09-28 6:12 [PATCH] KVM: LAPIC: Tune lapic_timer_advance_ns automatically Wanpeng Li 2018-10-01 14:00 ` Paolo Bonzini @ 2018-10-07 21:02 ` Liran Alon 2018-10-08 10:59 ` Wanpeng Li 1 sibling, 1 reply; 6+ messages in thread From: Liran Alon @ 2018-10-07 21:02 UTC (permalink / raw) To: Wanpeng Li; +Cc: linux-kernel, kvm, Paolo Bonzini, Radim Krčmář > On 28 Sep 2018, at 9:12, Wanpeng Li <kernellwp@gmail.com> 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 d0659d946be05 (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> > Signed-off-by: Wanpeng Li <wanpengli@tencent.com> > --- > arch/x86/kvm/lapic.c | 7 +++++++ > arch/x86/kvm/x86.c | 2 +- > 2 files changed, 8 insertions(+), 1 deletion(-) > > diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c > index fbb0e6d..b756f12 100644 > --- a/arch/x86/kvm/lapic.c > +++ b/arch/x86/kvm/lapic.c > @@ -70,6 +70,8 @@ > #define APIC_BROADCAST 0xFF > #define X2APIC_BROADCAST 0xFFFFFFFFul > > +static bool __read_mostly lapic_timer_advance_adjust_done = false; > + > static inline int apic_test_vector(int vec, void *bitmap) > { > return test_bit(VEC_POS(vec), (bitmap) + REG_POS(vec)); > @@ -1492,6 +1494,11 @@ 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) { > + lapic_timer_advance_ns += (s64)(guest_tsc - tsc_deadline) / 8; I don’t understand how this “/ 8” converts between guest TSC units to host nanoseconds. I think that instead you should do something like: s64 ns = (s64)(guest_tsc - tsc_deadline) * 1000000ULL; do_div(ns, vcpu->arch.virtual_tsc_khz); lapic_timer_advance_ns += ns; > + if (abs(guest_tsc - tsc_deadline) < 100) I would put this “100” hard-coded value as some “#define” to make code more clear. > + 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 edbf00e..e865d12 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 lapic_timer_advance_ns = 1000; > module_param(lapic_timer_advance_ns, uint, S_IRUGO | S_IWUSR); > EXPORT_SYMBOL_GPL(lapic_timer_advance_ns); > > -- > 2.7.4 > ^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH] KVM: LAPIC: Tune lapic_timer_advance_ns automatically 2018-10-07 21:02 ` Liran Alon @ 2018-10-08 10:59 ` Wanpeng Li 2018-10-08 12:04 ` Liran Alon 0 siblings, 1 reply; 6+ messages in thread From: Wanpeng Li @ 2018-10-08 10:59 UTC (permalink / raw) To: Liran Alon; +Cc: LKML, kvm, Paolo Bonzini, Radim Krcmar On Mon, 8 Oct 2018 at 05:02, Liran Alon <liran.alon@oracle.com> wrote: > > > > > On 28 Sep 2018, at 9:12, Wanpeng Li <kernellwp@gmail.com> 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 d0659d946be05 (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> > > Signed-off-by: Wanpeng Li <wanpengli@tencent.com> > > --- > > arch/x86/kvm/lapic.c | 7 +++++++ > > arch/x86/kvm/x86.c | 2 +- > > 2 files changed, 8 insertions(+), 1 deletion(-) > > > > diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c > > index fbb0e6d..b756f12 100644 > > --- a/arch/x86/kvm/lapic.c > > +++ b/arch/x86/kvm/lapic.c > > @@ -70,6 +70,8 @@ > > #define APIC_BROADCAST 0xFF > > #define X2APIC_BROADCAST 0xFFFFFFFFul > > > > +static bool __read_mostly lapic_timer_advance_adjust_done = false; > > + > > static inline int apic_test_vector(int vec, void *bitmap) > > { > > return test_bit(VEC_POS(vec), (bitmap) + REG_POS(vec)); > > @@ -1492,6 +1494,11 @@ 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) { > > + lapic_timer_advance_ns += (s64)(guest_tsc - tsc_deadline) / 8; > > I don’t understand how this “/ 8” converts between guest TSC units to host nanoseconds. Oh, I miss it. In addition, /8 here I mean adjust lapic_timer_advance_ns step by step. I can observe big fluctuated value between early and late when running real guest os like linux instead of kvm-unit-tests. After more testing, I saw lapic_timer_advance_ns can be overflow since the delta between guest_tsc and tsc_deadline is too huge. > > I think that instead you should do something like: > s64 ns = (s64)(guest_tsc - tsc_deadline) * 1000000ULL; > do_div(ns, vcpu->arch.virtual_tsc_khz); > lapic_timer_advance_ns += ns; > > > + if (abs(guest_tsc - tsc_deadline) < 100) > > I would put this “100” hard-coded value as some “#define” to make code more clear. How about something like below: diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c index fbb0e6d..354eb13c 100644 --- a/arch/x86/kvm/lapic.c +++ b/arch/x86/kvm/lapic.c @@ -70,6 +70,9 @@ #define APIC_BROADCAST 0xFF #define X2APIC_BROADCAST 0xFFFFFFFFul +static bool __read_mostly lapic_timer_advance_adjust_done = false; +#define LAPIC_TIMER_ADVANCE_ADJUST_DONE 100 + static inline int apic_test_vector(int vec, void *bitmap) { return test_bit(VEC_POS(vec), (bitmap) + REG_POS(vec)); @@ -1472,7 +1475,7 @@ 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 +1495,19 @@ 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) { + 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 / 8); + } else { + 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 / 8); + } + if (ns < 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); ^ permalink raw reply related [flat|nested] 6+ messages in thread
* Re: [PATCH] KVM: LAPIC: Tune lapic_timer_advance_ns automatically 2018-10-08 10:59 ` Wanpeng Li @ 2018-10-08 12:04 ` Liran Alon 2018-10-09 2:08 ` Wanpeng Li 0 siblings, 1 reply; 6+ messages in thread From: Liran Alon @ 2018-10-08 12:04 UTC (permalink / raw) To: Wanpeng Li; +Cc: LKML, kvm, Paolo Bonzini, Radim Krcmar > On 8 Oct 2018, at 13:59, Wanpeng Li <kernellwp@gmail.com> wrote: > > On Mon, 8 Oct 2018 at 05:02, Liran Alon <liran.alon@oracle.com> wrote: >> >> >> >>> On 28 Sep 2018, at 9:12, Wanpeng Li <kernellwp@gmail.com> 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 d0659d946be05 (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> >>> Signed-off-by: Wanpeng Li <wanpengli@tencent.com> >>> --- >>> arch/x86/kvm/lapic.c | 7 +++++++ >>> arch/x86/kvm/x86.c | 2 +- >>> 2 files changed, 8 insertions(+), 1 deletion(-) >>> >>> diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c >>> index fbb0e6d..b756f12 100644 >>> --- a/arch/x86/kvm/lapic.c >>> +++ b/arch/x86/kvm/lapic.c >>> @@ -70,6 +70,8 @@ >>> #define APIC_BROADCAST 0xFF >>> #define X2APIC_BROADCAST 0xFFFFFFFFul >>> >>> +static bool __read_mostly lapic_timer_advance_adjust_done = false; >>> + >>> static inline int apic_test_vector(int vec, void *bitmap) >>> { >>> return test_bit(VEC_POS(vec), (bitmap) + REG_POS(vec)); >>> @@ -1492,6 +1494,11 @@ 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) { >>> + lapic_timer_advance_ns += (s64)(guest_tsc - tsc_deadline) / 8; >> >> I don’t understand how this “/ 8” converts between guest TSC units to host nanoseconds. > > Oh, I miss it. In addition, /8 here I mean adjust > lapic_timer_advance_ns step by step. I can observe big fluctuated If that’s the case, I would also put the “8” as a #define to make it more clear of it’s purpose. > value between early and late when running real guest os like linux > instead of kvm-unit-tests. After more testing, I saw > lapic_timer_advance_ns can be overflow since the delta between > guest_tsc and tsc_deadline is too huge. > >> >> I think that instead you should do something like: >> s64 ns = (s64)(guest_tsc - tsc_deadline) * 1000000ULL; >> do_div(ns, vcpu->arch.virtual_tsc_khz); >> lapic_timer_advance_ns += ns; >> >>> + if (abs(guest_tsc - tsc_deadline) < 100) >> >> I would put this “100” hard-coded value as some “#define” to make code more clear. > > How about something like below: > > diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c > index fbb0e6d..354eb13c 100644 > --- a/arch/x86/kvm/lapic.c > +++ b/arch/x86/kvm/lapic.c > @@ -70,6 +70,9 @@ > #define APIC_BROADCAST 0xFF > #define X2APIC_BROADCAST 0xFFFFFFFFul > > +static bool __read_mostly lapic_timer_advance_adjust_done = false; > +#define LAPIC_TIMER_ADVANCE_ADJUST_DONE 100 > + > static inline int apic_test_vector(int vec, void *bitmap) > { > return test_bit(VEC_POS(vec), (bitmap) + REG_POS(vec)); > @@ -1472,7 +1475,7 @@ 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 +1495,19 @@ 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) { > + 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 / 8); > + } else { > + 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 / 8); > + } > + if (ns < LAPIC_TIMER_ADVANCE_ADJUST_DONE) Didn’t you meant to compare here that abs(guest_tsc - tsc_deadline) < LAPIC_TIMER_ADVANCE_ADJUST_DONE? This is also a good example on why I would also rename LAPIC_TIMER_ADVANCE_ADJUST_DONE to something which indicates it represents a number in guest TSC units. > + 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); ^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH] KVM: LAPIC: Tune lapic_timer_advance_ns automatically 2018-10-08 12:04 ` Liran Alon @ 2018-10-09 2:08 ` Wanpeng Li 0 siblings, 0 replies; 6+ messages in thread From: Wanpeng Li @ 2018-10-09 2:08 UTC (permalink / raw) To: Liran Alon; +Cc: LKML, kvm, Paolo Bonzini, Radim Krcmar On Mon, 8 Oct 2018 at 20:04, Liran Alon <liran.alon@oracle.com> wrote: > > > > > On 8 Oct 2018, at 13:59, Wanpeng Li <kernellwp@gmail.com> wrote: > > > > On Mon, 8 Oct 2018 at 05:02, Liran Alon <liran.alon@oracle.com> wrote: > >> > >> > >> > >>> On 28 Sep 2018, at 9:12, Wanpeng Li <kernellwp@gmail.com> 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 d0659d946be05 (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> > >>> Signed-off-by: Wanpeng Li <wanpengli@tencent.com> > >>> --- > >>> arch/x86/kvm/lapic.c | 7 +++++++ > >>> arch/x86/kvm/x86.c | 2 +- > >>> 2 files changed, 8 insertions(+), 1 deletion(-) > >>> > >>> diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c > >>> index fbb0e6d..b756f12 100644 > >>> --- a/arch/x86/kvm/lapic.c > >>> +++ b/arch/x86/kvm/lapic.c > >>> @@ -70,6 +70,8 @@ > >>> #define APIC_BROADCAST 0xFF > >>> #define X2APIC_BROADCAST 0xFFFFFFFFul > >>> > >>> +static bool __read_mostly lapic_timer_advance_adjust_done = false; > >>> + > >>> static inline int apic_test_vector(int vec, void *bitmap) > >>> { > >>> return test_bit(VEC_POS(vec), (bitmap) + REG_POS(vec)); > >>> @@ -1492,6 +1494,11 @@ 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) { > >>> + lapic_timer_advance_ns += (s64)(guest_tsc - tsc_deadline) / 8; > >> > >> I don’t understand how this “/ 8” converts between guest TSC units to host nanoseconds. > > > > Oh, I miss it. In addition, /8 here I mean adjust > > lapic_timer_advance_ns step by step. I can observe big fluctuated > > If that’s the case, I would also put the “8” as a #define to make it more clear of it’s purpose. > > > value between early and late when running real guest os like linux > > instead of kvm-unit-tests. After more testing, I saw > > lapic_timer_advance_ns can be overflow since the delta between > > guest_tsc and tsc_deadline is too huge. > > > >> > >> I think that instead you should do something like: > >> s64 ns = (s64)(guest_tsc - tsc_deadline) * 1000000ULL; > >> do_div(ns, vcpu->arch.virtual_tsc_khz); > >> lapic_timer_advance_ns += ns; > >> > >>> + if (abs(guest_tsc - tsc_deadline) < 100) > >> > >> I would put this “100” hard-coded value as some “#define” to make code more clear. > > > > How about something like below: > > > > diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c > > index fbb0e6d..354eb13c 100644 > > --- a/arch/x86/kvm/lapic.c > > +++ b/arch/x86/kvm/lapic.c > > @@ -70,6 +70,9 @@ > > #define APIC_BROADCAST 0xFF > > #define X2APIC_BROADCAST 0xFFFFFFFFul > > > > +static bool __read_mostly lapic_timer_advance_adjust_done = false; > > +#define LAPIC_TIMER_ADVANCE_ADJUST_DONE 100 > > + > > static inline int apic_test_vector(int vec, void *bitmap) > > { > > return test_bit(VEC_POS(vec), (bitmap) + REG_POS(vec)); > > @@ -1472,7 +1475,7 @@ 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 +1495,19 @@ 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) { > > + 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 / 8); > > + } else { > > + 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 / 8); > > + } > > + if (ns < LAPIC_TIMER_ADVANCE_ADJUST_DONE) > > Didn’t you meant to compare here that abs(guest_tsc - tsc_deadline) < LAPIC_TIMER_ADVANCE_ADJUST_DONE? > This is also a good example on why I would also rename LAPIC_TIMER_ADVANCE_ADJUST_DONE to something > which indicates it represents a number in guest TSC units. Done in v2. Regards, Wanpeng Li ^ permalink raw reply [flat|nested] 6+ messages in thread
end of thread, other threads:[~2018-10-09 2:07 UTC | newest] Thread overview: 6+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- 2018-09-28 6:12 [PATCH] KVM: LAPIC: Tune lapic_timer_advance_ns automatically Wanpeng Li 2018-10-01 14:00 ` Paolo Bonzini 2018-10-07 21:02 ` Liran Alon 2018-10-08 10:59 ` Wanpeng Li 2018-10-08 12:04 ` Liran Alon 2018-10-09 2:08 ` Wanpeng Li
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