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

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Date:   Tue, 7 Jul 2020 19:43:28 +0300
From:   Alexey Budankov <alexey.budankov@...ux.intel.com>
To:     Jiri Olsa <jolsa@...hat.com>
Cc:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Andi Kleen <ak@...ux.intel.com>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v9 11/15] perf stat: implement control commands handling


On 07.07.2020 19:05, Jiri Olsa wrote:
> On Tue, Jul 07, 2020 at 05:55:14PM +0300, Alexey Budankov wrote:
> 
> SNIP
> 
>> process_evlist() now looks suboptimal since record mode code directly calls evlist__ctlfd_process()
>> and then handles returned command specifically to the mode. So in v10 I replaced process_evlist()
>> call with direct evlist__ctlfd_process() call and then handling the returned command by printing
>> command msg tag and counter values in the required order. Like this:
>>
>> +		clock_gettime(CLOCK_MONOTONIC, &time_start);
>> +		if (!(evlist__poll(evsel_list, time_to_sleep) > 0)) { /* poll timeout or EINTR */
>> +			if (timeout)
>> +				break;
>> +			else
>> +				stop = handle_interval(interval, times);
>> +			time_to_sleep = sleep_time;
>> +		} else { /* fd revent */
>> +			if (evlist__ctlfd_process(evsel_list, &cmd) > 0) {
>> +				if (interval) {
>> +					switch (cmd) {
>> +					case EVLIST_CTL_CMD_ENABLE:
>> +						pr_info(EVLIST_ENABLED_MSG);
>> +						process_interval();
>> +						break;
>> +					case EVLIST_CTL_CMD_DISABLE:
>> +						process_interval();
>> +						pr_info(EVLIST_DISABLED_MSG);
>> +						break;
>> +					case EVLIST_CTL_CMD_ACK:
>> +					case EVLIST_CTL_CMD_UNSUPPORTED:
>> +					default:
>> +						break;
>> +					}
>> +				}
>> +			}
>> +			clock_gettime(CLOCK_MONOTONIC, &time_stop);
>> +			compute_tts(&time_start, &time_stop, &time_to_sleep);
>> +		}
> 
> 
> hum, why not just get the bool from process_evlist like below?

Yes, also possible and works. However it checks twice to implement
parts of logically the same work and passes the result using extra
memory: switch/case at process_evlist(), 'if' at dispatch_events(),
dispatch_events() should also call process_interval() instead of 
handle_interval() to avoid wasting of times counter for commands.

Alexey

> 
> jirka
> 
> 
> ---
> diff --git a/tools/perf/builtin-stat.c b/tools/perf/builtin-stat.c
> index 5021f7286422..32dd3de93f35 100644
> --- a/tools/perf/builtin-stat.c
> +++ b/tools/perf/builtin-stat.c
> @@ -485,20 +485,20 @@ 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 display = 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);
> +			display = true;
>  			break;
>  		case EVLIST_CTL_CMD_DISABLE:
> -			stop = handle_interval(interval, times);
>  			pr_info(EVLIST_DISABLED_MSG);
> +			display = true;
>  			break;
>  		case EVLIST_CTL_CMD_ACK:
>  		case EVLIST_CTL_CMD_UNSUPPORTED:
> @@ -507,7 +507,7 @@ static bool process_evlist(struct evlist *evlist, unsigned int interval, int *ti
>  		}
>  	}
>  
> -	return stop;
> +	return display;
>  }
>  
>  static void enable_counters(void)
> @@ -618,7 +618,8 @@ 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);
>  			clock_gettime(CLOCK_MONOTONIC, &time_stop);
>  			diff_timespec(&time_diff, &time_stop, &time_start);
>  			time_to_sleep -= time_diff.tv_sec * MSEC_PER_SEC +
>