Re: [PATCH v9 11/15] perf stat: implement control commands handling

[Alexey Budankov]

On 06.07.2020 15:34, Jiri Olsa wrote:
> On Fri, Jul 03, 2020 at 10:47:22AM +0300, Alexey Budankov wrote:
>>
>> Implement handling of 'enable' and 'disable' control commands
>> coming from control file descriptor. process_evlist() function
>> checks for events on control fds and makes required operations.
>> If poll event splits initiated timeout interval then the reminder
>> is calculated and still waited in the following poll() syscall.
>>
>> Signed-off-by: Alexey Budankov <alexey.budankov@xxxxxxxxxxxxxxx>
>> ---
>>  tools/perf/builtin-stat.c | 75 ++++++++++++++++++++++++++++-----------
>>  1 file changed, 55 insertions(+), 20 deletions(-)
>>
>> diff --git a/tools/perf/builtin-stat.c b/tools/perf/builtin-stat.c
>> index 9e4288ecf2b8..5021f7286422 100644
>> --- a/tools/perf/builtin-stat.c
>> +++ b/tools/perf/builtin-stat.c
>> @@ -485,6 +485,31 @@ static bool handle_interval(unsigned int interval, int *times)
>>  	return false;
>>  }
>>  
>> +static bool process_evlist(struct evlist *evlist, unsigned int interval, int *times)
>> +{
>> +	bool stop = false;
>> +	enum evlist_ctl_cmd cmd = EVLIST_CTL_CMD_UNSUPPORTED;
>> +
>> +	if (evlist__ctlfd_process(evlist, &cmd) > 0) {
>> +		switch (cmd) {
>> +		case EVLIST_CTL_CMD_ENABLE:
>> +			pr_info(EVLIST_ENABLED_MSG);
>> +			stop = handle_interval(interval, times);
>> +			break;
>> +		case EVLIST_CTL_CMD_DISABLE:
>> +			stop = handle_interval(interval, times);
> 
> I still don't understand why you call handle_interval in here
> 
> I don't see it being necessary.. you enable events and handle_interval,
> wil be called in the next iteration of dispatch_events, why complicate
> this function with that?

Printing event counts at the moment of command processing lets scripts
built on top of stat output to provide more plain and accurate metrics.
Otherwise it may get spikes in the beginning of the next time interval
because not all counts lay inside [Events enabled, Events disable]
If -I interval is large tail event count can be also large. Compare the
output below with the output in the cover letter. Either way is possible
but the latter one likely complicates the scripts I mentioned above.

perf=tools/perf/perf
${perf} stat -D -1 -e cpu-cycles -a -I 1000       \
             --control fd:${ctl_fd},${ctl_fd_ack} \
             -- sleep 40 &

Events disabled
#           time             counts unit events
     1.001100723      <not counted>      cpu-cycles                                                  
     2.003146566      <not counted>      cpu-cycles                                                  
     3.005073317      <not counted>      cpu-cycles                                                  
     4.006337062      <not counted>      cpu-cycles                                                  
Events enabled
enable acked(ack)
     5.011182000         54,128,692      cpu-cycles <===                                                 
     6.012300167      3,648,804,827      cpu-cycles                                                  
     7.013631689        590,438,536      cpu-cycles                                                  
     8.015558583        406,935,663      cpu-cycles                                                  
     9.017455505        407,806,862      cpu-cycles                                                  
    10.019300780        399,351,824      cpu-cycles                                                  
    11.021180025        404,584,417      cpu-cycles                                                  
    12.023033661        537,787,981      cpu-cycles                                                  
    13.024422354        699,395,364      cpu-cycles                                                  
    14.026325749        397,871,324      cpu-cycles                                                  
disable acked()
Events disabled
    15.027857981        396,956,159      cpu-cycles <===
    16.029279264      <not counted>      cpu-cycles                                                  
    17.031131311      <not counted>      cpu-cycles                                                  
    18.033010580      <not counted>      cpu-cycles                                                  
    19.034918883      <not counted>      cpu-cycles                                                  
enable acked(ack)
Events enabled
    20.036758793        183,544,975      cpu-cycles <===                                             
    21.038163289        419,054,544      cpu-cycles                                                  
    22.040108245        413,993,309      cpu-cycles                                                  
    23.042042365        403,584,493      cpu-cycles                                                  
    24.043985381        416,512,094      cpu-cycles                                                  
    25.045925682        401,513,429      cpu-cycles                                                  
#           time             counts unit events
    26.047822238        461,205,096      cpu-cycles                                                  
    27.049784263        414,319,162      cpu-cycles                                                  
    28.051745360        403,706,915      cpu-cycles                                                  
    29.053674600        416,502,883      cpu-cycles                                                  
disable acked()
Events disabled
    30.054750685        414,184,409      cpu-cycles <===

Alexey

> 
> thanks,
> jirka
>