linux-kernel - Re: [PATCH v8 12/13] perf record: implement control commands handling

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Date:   Wed, 24 Jun 2020 17:00:12 +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 v8 12/13] perf record: implement control commands handling


On 23.06.2020 17:54, Jiri Olsa wrote:
> On Wed, Jun 17, 2020 at 11:43:58AM +0300, Alexey Budankov wrote:
>>
>> Implement handling of 'enable' and 'disable' control commands
>> coming from control file descriptor.
>>
>> Signed-off-by: Alexey Budankov <alexey.budankov@...ux.intel.com>
>> ---
>>  tools/perf/builtin-record.c | 16 ++++++++++++++++
>>  1 file changed, 16 insertions(+)
>>
>> diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
>> index d0b29a1070a0..0394e068dde8 100644
>> --- a/tools/perf/builtin-record.c
>> +++ b/tools/perf/builtin-record.c
>> @@ -1527,6 +1527,7 @@ static int __cmd_record(struct record *rec, int argc, const char **argv)
>>  	bool disabled = false, draining = false;
>>  	int fd;
>>  	float ratio = 0;
>> +	enum evlist_ctl_cmd cmd = EVLIST_CTL_CMD_UNSUPPORTED;
>>  
>>  	atexit(record__sig_exit);
>>  	signal(SIGCHLD, sig_handler);
>> @@ -1830,6 +1831,21 @@ static int __cmd_record(struct record *rec, int argc, const char **argv)
>>  				alarm(rec->switch_output.time);
>>  		}
>>  
>> +		if (evlist__ctlfd_process(rec->evlist, &cmd) > 0) {
>> +			switch (cmd) {
>> +			case EVLIST_CTL_CMD_ENABLE:
>> +				pr_info(EVLIST_ENABLED_MSG);
>> +				break;
>> +			case EVLIST_CTL_CMD_DISABLE:
>> +				pr_info(EVLIST_DISABLED_MSG);
>> +				break;
>> +			case EVLIST_CTL_CMD_ACK:
>> +			case EVLIST_CTL_CMD_UNSUPPORTED:
>> +			default:
>> +				break;
>> +			}
>> +		}
> 
> so there's still the filter call like:
> 
>                         if (evlist__filter_pollfd(rec->evlist, POLLERR | POLLHUP) == 0)
>                                 draining = true;
> 
> it will never be 0 if the control fds are stil alive no?

Due to change in filter_pollfd() and preceding evlist__ctlfd_process() call
now control fd is not counted by filter_pollfd().

However event fds with .revents == 0 are not counted either and this breaks
the algorithm thus something more is still required to cover this gap.

~Alexey

> 
> jirka
>