Messages in this thread Patch in this message | | | Date | Fri, 2 Oct 2020 13:02:58 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH] perf/x86/intel: Fix n_metric for the canceled group |
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On Wed, Sep 30, 2020 at 07:29:35AM -0700, kan.liang@linux.intel.com wrote: > From: Kan Liang <kan.liang@linux.intel.com> > > When a group that has TopDown members is failed to be scheduled, any > later TopDown groups will not return valid values. > > Here is an example. > > A background perf that occupies all the GP counters and the fixed > counter 1. > $perf stat -e "{cycles,cycles,cycles,cycles,cycles,cycles,cycles, > cycles,cycles}:D" -a > > A user monitors a TopDown group. It works well, because the fixed > counter 3 and the PERF_METRICS are available. > $perf stat -x, --topdown -- ./workload > retiring,bad speculation,frontend bound,backend bound, > 18.0,16.1,40.4,25.5, > > Then the user tries to monitor a group that has TopDown members. > Because of the cycles event, the group is failed to be scheduled. > $perf stat -x, -e '{slots,topdown-retiring,topdown-be-bound, > topdown-fe-bound,topdown-bad-spec,cycles}' > -- ./workload > <not counted>,,slots,0,0.00,, > <not counted>,,topdown-retiring,0,0.00,, > <not counted>,,topdown-be-bound,0,0.00,, > <not counted>,,topdown-fe-bound,0,0.00,, > <not counted>,,topdown-bad-spec,0,0.00,, > <not counted>,,cycles,0,0.00,, > > The user tries to monitor a TopDown group again. It doesn't work anymore. > $perf stat -x, --topdown -- ./workload > > ,,,,, > > In a txn, cancel_txn() is to truncate the event_list for a canceled > group and update the number of events added in this transaction. > However, the number of TopDown events added in this transaction is not > updated. The kernel will probably fail to add new Topdown events. > > Check if the canceled group has Topdown events. If so, subtract the > TopDown events from n_metric accordingly. > > Fixes: 7b2c05a15d29 ("perf/x86/intel: Generic support for hardware TopDown metrics") > Reported-by: Andi Kleen <ak@linux.intel.com> > Reviewed-by: Andi Kleen <ak@linux.intel.com> > Signed-off-by: Kan Liang <kan.liang@linux.intel.com> > --- > arch/x86/events/core.c | 10 ++++++++++ > 1 file changed, 10 insertions(+) > > diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c > index 0f3d01562ded..4cb3ccbe2d62 100644 > --- a/arch/x86/events/core.c > +++ b/arch/x86/events/core.c > @@ -2017,6 +2017,7 @@ static void x86_pmu_cancel_txn(struct pmu *pmu) > { > unsigned int txn_flags; > struct cpu_hw_events *cpuc = this_cpu_ptr(&cpu_hw_events); > + int i; > > WARN_ON_ONCE(!cpuc->txn_flags); /* no txn in flight */ > > @@ -2031,6 +2032,15 @@ static void x86_pmu_cancel_txn(struct pmu *pmu) > */ > __this_cpu_sub(cpu_hw_events.n_added, __this_cpu_read(cpu_hw_events.n_txn)); > __this_cpu_sub(cpu_hw_events.n_events, __this_cpu_read(cpu_hw_events.n_txn)); > + > + /* Subtract Topdown events in the canceled group from n_metric */ > + if (x86_pmu.intel_cap.perf_metrics && cpuc->n_metric) { > + for (i = 0; i < cpuc->n_txn; i++) { > + if (is_metric_event(cpuc->event_list[i + cpuc->n_events])) > + __this_cpu_dec(cpu_hw_events.n_metric); > + } > + WARN_ON_ONCE(__this_cpu_read(cpu_hw_events.n_metric) < 0); > + } > perf_pmu_enable(pmu); > }
Urgh, I'd much rather we add n_txn_metric. But also, while looking at this, don't we have the same problem with n_pair ?
Something like this perhaps...
--- diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c index 757e49755e7c..9b7792c0b6fb 100644 --- a/arch/x86/events/core.c +++ b/arch/x86/events/core.c @@ -1066,6 +1066,7 @@ static int add_nr_metric_event(struct cpu_hw_events *cpuc, if (cpuc->n_metric == INTEL_TD_METRIC_NUM) return -EINVAL; cpuc->n_metric++; + cpuc->n_txn_metric++; } return 0; @@ -1089,8 +1090,10 @@ static int collect_event(struct cpu_hw_events *cpuc, struct perf_event *event, return -EINVAL; cpuc->event_list[n] = event; - if (is_counter_pair(&event->hw)) + if (is_counter_pair(&event->hw)) { cpuc->n_pair++; + cpuc->n_txn_pair++; + } return 0; } @@ -2062,6 +2065,8 @@ static void x86_pmu_start_txn(struct pmu *pmu, unsigned int txn_flags) perf_pmu_disable(pmu); __this_cpu_write(cpu_hw_events.n_txn, 0); + __this_cpu_write(cpu_hw_events.n_txn_metric, 0); + __this_cpu_write(cpu_hw_events.n_txn_pair, 0); } /* @@ -2087,6 +2092,8 @@ static void x86_pmu_cancel_txn(struct pmu *pmu) */ __this_cpu_sub(cpu_hw_events.n_added, __this_cpu_read(cpu_hw_events.n_txn)); __this_cpu_sub(cpu_hw_events.n_events, __this_cpu_read(cpu_hw_events.n_txn)); + __this_cpu_sub(cpu_hw_events.n_metric, __this_cpu_read(cpu_hw_events.n_txn_metric)); + __this_cpu_sub(cpu_hw_events.n_pair, __this_cpu_read(cpu_hw_events.n_txn_pair)); perf_pmu_enable(pmu); } diff --git a/arch/x86/events/perf_event.h b/arch/x86/events/perf_event.h index 345442410a4d..6348105b6d30 100644 --- a/arch/x86/events/perf_event.h +++ b/arch/x86/events/perf_event.h @@ -235,6 +235,8 @@ struct cpu_hw_events { they've never been enabled yet */ int n_txn; /* the # last events in the below arrays; added in the current transaction */ + int n_txn_metric; + int n_txn_pair; int assign[X86_PMC_IDX_MAX]; /* event to counter assignment */ u64 tags[X86_PMC_IDX_MAX];
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