linux-kernel - Re: [PATCH v3 8/9] perf record: implement control commands handling

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Date:   Wed, 20 May 2020 14:38:33 +0200
From:   Jiri Olsa <jolsa@...hat.com>
To:     Alexey Budankov <alexey.budankov@...ux.intel.com>
Cc:     Arnaldo Carvalho de Melo <acme@...hat.com>,
        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 v3 8/9] perf record: implement control commands handling

On Wed, May 13, 2020 at 11:04:25AM +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 | 18 +++++++++++++++++-
>  1 file changed, 17 insertions(+), 1 deletion(-)
> 
> diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
> index 50dc2fe626e5..72f388623364 100644
> --- a/tools/perf/builtin-record.c
> +++ b/tools/perf/builtin-record.c
> @@ -1505,6 +1505,7 @@ 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);
> @@ -1802,8 +1803,23 @@ static int __cmd_record(struct record *rec, int argc, const char **argv)
>  			 * Propagate error, only if there's any. Ignore positive
>  			 * number of returned events and interrupt error.
>  			 */
> -			if (err > 0 || (err < 0 && errno == EINTR))
> +			if (err > 0 || (err < 0 && errno == EINTR)) {
>  				err = 0;
> +				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 this will be processed only when:

	if (hits == rec->samples) {

what if there's always somethign in the buffer? will this stall?

>  			waking++;
>  
>  			if (evlist__filter_pollfd(rec->evlist, POLLERR | POLLHUP) == 0)

evlist__filter_pollfd will trigger draining if all the maps are closed,
but there's one more fd in pollfd now, will this prevent draining?

I wonder this would fit better to the sideband thread (util/sideband_evlist.c)
so we don't disturb the main thread with another check

jirka

> -- 
> 2.24.1
> 
>