Messages in this thread | | | Subject | Re: [PATCH v2] KVM: x86/pmu: Reduce counter period change overhead and delay the effective time | From | Like Xu <> | Date | Wed, 8 Apr 2020 22:04:34 +0800 |
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Hi Paolo,
Could you please take a look at this patch? If there is anything needs to be improved, please let me know.
Thanks, Like Xu
On 2020/3/26 20:47, Like Xu wrote: > Anyone to help review this change? > > Thanks, > Like Xu > > On 2020/3/17 16:14, Like Xu wrote: >> The cost of perf_event_period() is unstable, and when the guest samples >> multiple events, the overhead increases dramatically (5378 ns on E5-2699). >> >> For a non-running counter, the effective time of the new period is when >> its corresponding enable bit is enabled. Calling perf_event_period() >> in advance is superfluous. For a running counter, it's safe to delay the >> effective time until the KVM_REQ_PMU event is handled. If there are >> multiple perf_event_period() calls before handling KVM_REQ_PMU, >> it helps to reduce the total cost. >> >> Signed-off-by: Like Xu <like.xu@linux.intel.com> >> --- >> arch/x86/kvm/pmu.c | 11 ----------- >> arch/x86/kvm/pmu.h | 11 +++++++++++ >> arch/x86/kvm/vmx/pmu_intel.c | 10 ++++------ >> 3 files changed, 15 insertions(+), 17 deletions(-) >> >> diff --git a/arch/x86/kvm/pmu.c b/arch/x86/kvm/pmu.c >> index d1f8ca57d354..527a8bb85080 100644 >> --- a/arch/x86/kvm/pmu.c >> +++ b/arch/x86/kvm/pmu.c >> @@ -437,17 +437,6 @@ void kvm_pmu_init(struct kvm_vcpu *vcpu) >> kvm_pmu_refresh(vcpu); >> } >> -static inline bool pmc_speculative_in_use(struct kvm_pmc *pmc) >> -{ >> - struct kvm_pmu *pmu = pmc_to_pmu(pmc); >> - >> - if (pmc_is_fixed(pmc)) >> - return fixed_ctrl_field(pmu->fixed_ctr_ctrl, >> - pmc->idx - INTEL_PMC_IDX_FIXED) & 0x3; >> - >> - return pmc->eventsel & ARCH_PERFMON_EVENTSEL_ENABLE; >> -} >> - >> /* Release perf_events for vPMCs that have been unused for a full time >> slice. */ >> void kvm_pmu_cleanup(struct kvm_vcpu *vcpu) >> { >> diff --git a/arch/x86/kvm/pmu.h b/arch/x86/kvm/pmu.h >> index d7da2b9e0755..cd112e825d2c 100644 >> --- a/arch/x86/kvm/pmu.h >> +++ b/arch/x86/kvm/pmu.h >> @@ -138,6 +138,17 @@ static inline u64 get_sample_period(struct kvm_pmc >> *pmc, u64 counter_value) >> return sample_period; >> } >> +static inline bool pmc_speculative_in_use(struct kvm_pmc *pmc) >> +{ >> + struct kvm_pmu *pmu = pmc_to_pmu(pmc); >> + >> + if (pmc_is_fixed(pmc)) >> + return fixed_ctrl_field(pmu->fixed_ctr_ctrl, >> + pmc->idx - INTEL_PMC_IDX_FIXED) & 0x3; >> + >> + return pmc->eventsel & ARCH_PERFMON_EVENTSEL_ENABLE; >> +} >> + >> void reprogram_gp_counter(struct kvm_pmc *pmc, u64 eventsel); >> void reprogram_fixed_counter(struct kvm_pmc *pmc, u8 ctrl, int fixed_idx); >> void reprogram_counter(struct kvm_pmu *pmu, int pmc_idx); >> diff --git a/arch/x86/kvm/vmx/pmu_intel.c b/arch/x86/kvm/vmx/pmu_intel.c >> index 7c857737b438..20f654a0c09b 100644 >> --- a/arch/x86/kvm/vmx/pmu_intel.c >> +++ b/arch/x86/kvm/vmx/pmu_intel.c >> @@ -263,15 +263,13 @@ static int intel_pmu_set_msr(struct kvm_vcpu *vcpu, >> struct msr_data *msr_info) >> if (!msr_info->host_initiated) >> data = (s64)(s32)data; >> pmc->counter += data - pmc_read_counter(pmc); >> - if (pmc->perf_event) >> - perf_event_period(pmc->perf_event, >> - get_sample_period(pmc, data)); >> + if (pmc_speculative_in_use(pmc)) >> + kvm_make_request(KVM_REQ_PMU, vcpu); >> return 0; >> } else if ((pmc = get_fixed_pmc(pmu, msr))) { >> pmc->counter += data - pmc_read_counter(pmc); >> - if (pmc->perf_event) >> - perf_event_period(pmc->perf_event, >> - get_sample_period(pmc, data)); >> + if (pmc_speculative_in_use(pmc)) >> + kvm_make_request(KVM_REQ_PMU, vcpu); >> return 0; >> } else if ((pmc = get_gp_pmc(pmu, msr, MSR_P6_EVNTSEL0))) { >> if (data == pmc->eventsel) >> >
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