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perf/x86: Fix n_metric for cancelled txn

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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.

Fixes: 7b2c05a15d ("perf/x86/intel: Generic support for hardware TopDown metrics")
Reported-by: Andi Kleen <ak@linux.intel.com>
Reported-by: Kan Liang <kan.liang@linux.intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Tested-by: Kan Liang <kan.liang@linux.intel.com>
Link: https://lkml.kernel.org/r/20201005082611.GH2628@hirez.programming.kicks-ass.net
This commit is contained in:
Peter Zijlstra 2020-10-05 10:10:24 +02:00
parent 871a93b0aa
commit 3dbde69575
2 changed files with 4 additions and 0 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

3
arch/x86/events/core.c
View file

@ -1041,6 +1041,7 @@ 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;
@ -2009,6 +2010,7 @@ 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_pair, 0);
__this_cpu_write(cpu_hw_events.n_txn_metric, 0);
}
/*
@ -2035,6 +2037,7 @@ 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_pair, __this_cpu_read(cpu_hw_events.n_txn_pair));
__this_cpu_sub(cpu_hw_events.n_metric, __this_cpu_read(cpu_hw_events.n_txn_metric));
perf_pmu_enable(pmu);
}

1
arch/x86/events/perf_event.h
View file

@ -236,6 +236,7 @@ struct cpu_hw_events {
int n_txn; /* the # last events in the below arrays;
added in the current transaction */
int n_txn_pair;
int n_txn_metric;
int assign[X86_PMC_IDX_MAX]; /* event to counter assignment */
u64 tags[X86_PMC_IDX_MAX];