On Sun, May 19, 2019 at 06:05:59PM +0800, Xiang Zheng wrote: > Guest will adjust the sample period and set PMU counter value when > it takes a long time to handle the PMU interrupts. > > However, we don't have a corresponding change on the virtual PMU > which is emulated via a perf event. It could cause a large number > of PMU interrupts injected to guest. Then guest will get hang for > handling these interrupts. Yes this is indeed an issue. I believe I've addressed this in my 'chained pmu' series - the relevant patch is here... https://lists.cs.columbia.edu/pipermail/kvmarm/2019-May/035933.html Some other comments below. > > So update the sample_period of perf event if the counter value is > changed to avoid this case. > > Signed-off-by: Xiang Zheng <zhengxiang9@xxxxxxxxxx> > --- > virt/kvm/arm/pmu.c | 54 +++++++++++++++++++++++++++++++++++++++++++++--------- > 1 file changed, 45 insertions(+), 9 deletions(-) > > diff --git a/virt/kvm/arm/pmu.c b/virt/kvm/arm/pmu.c > index 1c5b76c..cbad3ec 100644 > --- a/virt/kvm/arm/pmu.c > +++ b/virt/kvm/arm/pmu.c > @@ -24,6 +24,11 @@ > #include <kvm/arm_pmu.h> > #include <kvm/arm_vgic.h> > > +static void kvm_pmu_stop_counter(struct kvm_vcpu *vcpu, struct kvm_pmc *pmc); > +static struct perf_event *kvm_pmu_create_perf_event(struct kvm_vcpu *vcpu, > + struct kvm_pmc *pmc, > + struct perf_event_attr *attr); > + > /** > * kvm_pmu_get_counter_value - get PMU counter value > * @vcpu: The vcpu pointer > @@ -57,11 +62,29 @@ u64 kvm_pmu_get_counter_value(struct kvm_vcpu *vcpu, u64 select_idx) > */ > void kvm_pmu_set_counter_value(struct kvm_vcpu *vcpu, u64 select_idx, u64 val) > { > - u64 reg; > + u64 reg, counter, old_sample_period; > + struct kvm_pmu *pmu = &vcpu->arch.pmu; > + struct kvm_pmc *pmc = &pmu->pmc[select_idx]; > + struct perf_event *event; > + struct perf_event_attr attr; > > reg = (select_idx == ARMV8_PMU_CYCLE_IDX) > ? PMCCNTR_EL0 : PMEVCNTR0_EL0 + select_idx; > __vcpu_sys_reg(vcpu, reg) += (s64)val - kvm_pmu_get_counter_value(vcpu, select_idx); > + > + if (pmc->perf_event) { > + attr = pmc->perf_event->attr; > + old_sample_period = attr.sample_period; > + counter = kvm_pmu_get_counter_value(vcpu, select_idx); > + attr.sample_period = (-counter) & pmc->bitmask; > + if (attr.sample_period == old_sample_period) > + return; I'd be interested to know how often this would evaluate to true. > + > + kvm_pmu_stop_counter(vcpu, pmc); > + event = kvm_pmu_create_perf_event(vcpu, pmc, &attr); I'm not sure it's necessary to change the prototype of kvm_pmu_create_perf_event as this function will recalculate the sample period based on the updated counter value anyway. Thanks, Andrew Murray > + if (event) > + pmc->perf_event = event; > + } > } > > /** > @@ -303,6 +326,24 @@ static void kvm_pmu_perf_overflow(struct perf_event *perf_event, > } > } > > +static struct perf_event *kvm_pmu_create_perf_event(struct kvm_vcpu *vcpu, > + struct kvm_pmc *pmc, > + struct perf_event_attr *attr) > +{ > + struct perf_event *event; > + > + event = perf_event_create_kernel_counter(attr, -1, current, > + kvm_pmu_perf_overflow, pmc); > + > + if (IS_ERR(event)) { > + pr_err_once("kvm: pmu event creation failed %ld\n", > + PTR_ERR(event)); > + return NULL; > + } > + > + return event; > +} > + > /** > * kvm_pmu_software_increment - do software increment > * @vcpu: The vcpu pointer > @@ -416,15 +457,10 @@ void kvm_pmu_set_counter_event_type(struct kvm_vcpu *vcpu, u64 data, > /* The initial sample period (overflow count) of an event. */ > attr.sample_period = (-counter) & pmc->bitmask; > > - event = perf_event_create_kernel_counter(&attr, -1, current, > - kvm_pmu_perf_overflow, pmc); > - if (IS_ERR(event)) { > - pr_err_once("kvm: pmu event creation failed %ld\n", > - PTR_ERR(event)); > - return; > - } > + event = kvm_pmu_create_perf_event(vcpu, pmc, &attr); > > - pmc->perf_event = event; > + if (event) > + pmc->perf_event = event; > } > > bool kvm_arm_support_pmu_v3(void) > -- > 1.8.3.1 > > > _______________________________________________ > kvmarm mailing list > kvmarm@xxxxxxxxxxxxxxxxxxxxx > https://lists.cs.columbia.edu/mailman/listinfo/kvmarm _______________________________________________ kvmarm mailing list kvmarm@xxxxxxxxxxxxxxxxxxxxx https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
