On 2019/5/22 0:44, Andrew Murray wrote: > 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. > Sorry for that I didn't notice your patches... I will test your patch series. >> >> 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. > I have counted it while running my test script, the result shows that there are 1552288 times evaluated to true and 8294235 times not. I think different testcases may produce different results. >> + >> + 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. > In this patch, kvm_pmu_create_perf_event() will not recalculate the sample period. Maybe you confuse it with your patch.:) > 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 > > . > -- Thanks, Xiang _______________________________________________ kvmarm mailing list kvmarm@xxxxxxxxxxxxxxxxxxxxx https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
