From: Like Xu <like.xu@linux.intel.com>
To: pbonzini@redhat.com
Cc: ehankland@google.com, jmattson@google.com, joro@8bytes.org,
kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
sean.j.christopherson@intel.com, vkuznets@redhat.com,
wanpengli@tencent.com
Subject: Re: [PATCH v2] KVM: x86/pmu: Reduce counter period change overhead and delay the effective time
Date: Thu, 26 Mar 2020 20:47:53 +0800 [thread overview]
Message-ID: <1528e1b4-3dee-161b-9463-57471263b5a8@linux.intel.com> (raw)
In-Reply-To: <20200317081458.88714-1-like.xu@linux.intel.com>
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)
>
next prev parent reply other threads:[~2020-03-26 12:47 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-03-17 7:53 [PATCH] kvm/x86: Reduce counter period change overhead and delay the effective time Like Xu
2020-03-17 8:00 ` Like Xu
2020-03-17 8:14 ` [PATCH v2] KVM: x86/pmu: " Like Xu
2020-03-26 12:47 ` Like Xu [this message]
2020-04-08 14:04 ` Like Xu
2020-04-16 14:41 ` Like Xu
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