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Peter Zijlstra 3dbde69575 perf/x86: Fix n_metric for cancelled txn

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: 7b2c05a15d29 ("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

2020-10-06 15:18:17 +02:00

amd

x86/events/amd/iommu: Fix sizeof mismatch

2020-10-03 16:30:56 +02:00

intel

perf/x86/intel: Check perf metrics feature for each CPU

2020-10-03 16:30:56 +02:00

zhaoxin

x86/perf: Fix a typo

2020-07-22 10:22:08 +02:00

core.c

perf/x86: Fix n_metric for cancelled txn