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

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Message-ID: <20200625170737.GJ2719003@krava>
Date:   Thu, 25 Jun 2020 19:07:37 +0200
From:   Jiri Olsa <jolsa@...hat.com>
To:     Alexey Budankov <alexey.budankov@...ux.intel.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 Wed, Jun 24, 2020 at 05:55:02PM +0300, Alexey Budankov wrote:
> 
> On 24.06.2020 17:00, Alexey Budankov wrote:
> > 
> > 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().
> And evlist__ctlfd_process() still should be called second time right
> after evlist_poll() but prior filter_polfd().

aaah it's set to zero in here:

        if (entries[ctlfd_pos].revents & (POLLHUP | POLLERR))
                evlist__finalize_ctlfd(evlist);
        else
                entries[ctlfd_pos].revents = 0;

yea, that's bad.. another reason to call it a hack

jirka

> 
> ~Alexey
> 
> > 
> > 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
> >>
>