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Subject: Re: [PATCH v9 11/15] perf stat: implement control commands handling
To:     Jiri Olsa <jolsa@redhat.com>
Cc:     Arnaldo Carvalho de Melo <acme@kernel.org>,
        Namhyung Kim <namhyung@kernel.org>,
        Alexander Shishkin <alexander.shishkin@linux.intel.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@redhat.com>,
        Andi Kleen <ak@linux.intel.com>,
        linux-kernel <linux-kernel@vger.kernel.org>
References: <a4d5db4a-f25c-38dc-1c41-321a886cb122@linux.intel.com>
 <21669f5a-6220-df0a-09f1-b73b32487f23@linux.intel.com>
 <20200706123436.GD3401866@krava>
 <6cf91811-ea6a-3c7c-8bbf-7f96bfa1fc82@linux.intel.com>
 <20200706193418.GB3424581@krava>
From:   Alexey Budankov <alexey.budankov@linux.intel.com>
Organization: Intel Corp.
Message-ID: <b28806b9-b66e-aa2e-5425-4d9f00341387@linux.intel.com>
Date:   Tue, 7 Jul 2020 16:07:42 +0300
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On 06.07.2020 22:34, Jiri Olsa wrote:
> On Mon, Jul 06, 2020 at 05:47:54PM +0300, Alexey Budankov wrote:
>>
>> 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@linux.intel.com>
>>>> ---
>>>>  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 <===
> 
> ok, but we could still take handle_interval out of process_evlist
> and the interval process will be more clear for me (with some
> additional comments in the code) ... perhaps something like below?
> 
> thanks,
> jirka
> 
> 
> ---
> diff --git a/tools/perf/builtin-stat.c b/tools/perf/builtin-stat.c
> index 5021f7286422..af83bf6b2db0 100644
> --- a/tools/perf/builtin-stat.c
> +++ b/tools/perf/builtin-stat.c
> @@ -485,19 +485,18 @@ static bool handle_interval(unsigned int interval, int *times)
>  	return false;
>  }
>  
> -static bool process_evlist(struct evlist *evlist, unsigned int interval, int *times)
> +static bool process_evlist(struct evlist *evlist)
>  {
> -	bool stop = false;
>  	enum evlist_ctl_cmd cmd = EVLIST_CTL_CMD_UNSUPPORTED;
> +	bool enabled = false;
>  
>  	if (evlist__ctlfd_process(evlist, &cmd) > 0) {
>  		switch (cmd) {
>  		case EVLIST_CTL_CMD_ENABLE:
>  			pr_info(EVLIST_ENABLED_MSG);
> -			stop = handle_interval(interval, times);
> +			enabled = true;
>  			break;
>  		case EVLIST_CTL_CMD_DISABLE:
> -			stop = handle_interval(interval, times);
>  			pr_info(EVLIST_DISABLED_MSG);
>  			break;
>  		case EVLIST_CTL_CMD_ACK:
> @@ -507,7 +506,7 @@ static bool process_evlist(struct evlist *evlist, unsigned int interval, int *ti
>  		}
>  	}
>  
> -	return stop;
> +	return enabled;
>  }
>  
>  static void enable_counters(void)
> @@ -618,7 +617,8 @@ static int dispatch_events(bool forks, int timeout, int interval, int *times)
>  				stop = handle_interval(interval, times);
>  			time_to_sleep = sleep_time;
>  		} else { /* fd revent */
> -			stop = process_evlist(evsel_list, interval, times);
> +			if (process_evlist(evsel_list))
> +				stop = handle_interval(interval, times);

It will call only on enable command and lead to artificial spikes in the beginning of interval.
May be just take handle_interval() out of process_evlist() and have it similar to record case?

Alexey