Re: [PATCH] perf-record: Create events initially disabled -- again

David Ahern
2012-05-14T13:09:56Z

On 5/14/12 1:40 AM, Namhyung Kim wrote:
> Hi,
>
> On Sun, 13 May 2012 22:01:28 -0600, David Ahern wrote:
>> 764e16a changed perf-record to create events disabled by default and
>> enable them once perf initializations are done. This setting was dropped
>> by 0f82ebc. Now perf events are once again generated during perf's
>> initialization phase (e.g., generating maps).
>>
>> As an example, perf opens a lot of files at startup. Unpatched:
>>
>> perf record -e syscalls:sys_enter_open -ga -fo /tmp/perf.data -- sleep 1
>> [ perf record: Woken up 1 times to write data ]
>> [ perf record: Captured and wrote 0.087 MB /tmp/perf.data (~3798 samples) ]
>>
>> Using perf-script to look at the samples shows the perf command generating
>> 563 of the 566 total events.
>>
>> Patched:
>>
>> perf record -e syscalls:sys_enter_open -ga -fo /tmp/perf.data -- sleep 1
>> [ perf record: Woken up 1 times to write data ]
>> [ perf record: Captured and wrote 0.028 MB /tmp/perf.data (~1206 samples) ]
>>
>> Using perf-script to look at the samples does not show perf command.
>>
>> Signed-off-by: David Ahern<dsahern@gmail.com>
>> ---
>> tools/perf/util/evsel.c | 2 +-
>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
>> index 21eaab2..6710cfe 100644
>> --- a/tools/perf/util/evsel.c
>> +++ b/tools/perf/util/evsel.c
>> @@ -70,6 +70,7 @@ void perf_evsel__config(struct perf_evsel *evsel, struct perf_record_opts *opts,
>> struct perf_event_attr *attr =&evsel->attr;
>> int track = !evsel->idx; /* only the first counter needs these */
>>
>> + attr->disabled = 1;
>> attr->sample_id_all = opts->sample_id_all_missing ? 0 : 1;
>> attr->inherit = !opts->no_inherit;
>> attr->read_format = PERF_FORMAT_TOTAL_TIME_ENABLED |
>> @@ -138,7 +139,6 @@ void perf_evsel__config(struct perf_evsel *evsel, struct perf_record_opts *opts,
>>
>> if (perf_target__none(&opts->target)&&
>> (!opts->group || evsel == first)) {
>> - attr->disabled = 1;
>> attr->enable_on_exec = 1;
>> }
>> }
>
> A problem I see is that it'll break group handling again:
>
> $ ./perf stat -g sleep 1
>
> Performance counter stats for 'sleep 1':
>
> <not counted> task-clock
> <not counted> context-switches
> <not counted> CPU-migrations
> <not counted> page-faults
> <not counted> cycles
> <not counted> stalled-cycles-frontend
> <not counted> stalled-cycles-backend
> <not counted> instructions
> <not counted> branches
> <not counted> branch-misses
>
> 1.000868932 seconds time elapsed
>
> So I suggest changing perf_target__none() check to a proper one
> (perf_target__no_cpu? - the name might be changed soon) for your
> purpose.
>
> Thanks,
> Namhyung

Something else is wrong then. I tested that command (saw your patch in
the history) and it worked for me. Also, this code path does not affect
perf-stat -- it touches perf-record and perf-test only.

David