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 | Thu, 16 Apr 2020 22:41:57 +0800 |
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Ping.
On 2020/4/8 22:04, Like Xu wrote: > 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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