linux-kernel - Re: [PATCH v5 13/13] perf record: introduce --ctl-fd[-ack] options

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Date:   Fri, 5 Jun 2020 15:57:43 +0200
From:   Jiri Olsa <jolsa@...hat.com>
To:     Alexey Budankov <alexey.budankov@...ux.intel.com>
Cc:     Adrian Hunter <adrian.hunter@...el.com>,
        Andi Kleen <ak@...ux.intel.com>,
        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>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v5 13/13] perf record: introduce --ctl-fd[-ack] options

On Fri, Jun 05, 2020 at 04:15:52PM +0300, Alexey Budankov wrote:
> 
> On 05.06.2020 13:51, Jiri Olsa wrote:
> > On Tue, Jun 02, 2020 at 04:43:58PM +0300, Adrian Hunter wrote:
> >> On 2/06/20 12:12 pm, Alexey Budankov wrote:
> >>>
> >>> On 02.06.2020 11:32, Alexey Budankov wrote:
> >>>>
> >>>> On 02.06.2020 2:37, Andi Kleen wrote:
> >>>>>>> or a pathname, or including also the event default of "disabled".
> >>>>>>
> >>>>>> For my cases conversion of pathnames into open fds belongs to external
> >>>>>> controlling process e.g. like in the examples provided in the patch set.
> >>>>>> Not sure about "event default of 'disabled'"
> >>>>>
> >>>>> It would be nicer for manual use cases if perf supported the path names
> >>>>> directly like in Adrian's example, not needing a complex wrapper script.
> >>>>
> >>>> fds interface is required for VTune integration since VTune wants control
> >>>> over files creation aside of Perf tool process. The script demonstrates
> >>>> just one possible use case.
> >>>>
> >>>> Control files could easily be implemented on top of fds making open operations
> >>>> for paths and then initializing fds. Interface below is vague and with explicit
> >>>> options like below it could be more explicit:
> >>>> --ctl-file /tmp/my-perf.fifo --ctl-file-ack /tmp/my-perf-ack.fifo
> >>>
> >>> Or even clearer:
> >>>
> >>> --ctl-fifo /tmp/my-perf --ctl-fifo-ack /tmp/my-perf-ack
> >>
> >> If people are OK with having so many options, then that is fine by me.
> > 
> > the single option Adrian suggested seems better to me:
> > 
> >  --control
> >  --control 11
> >  --control 11,15
> 
> What if a user specifies fifos named like this above, not fds?
> 
> >  --control 11,15,disabled
> >  --control 11,,disabled
> >  --control /tmp/my-perf.fifo
> >  --control /tmp/my-perf.fifo,/tmp/my-perf-ack.fifo
> 
> What if a user wants not fifos but other type of comm channels?
> 
> >  --control /tmp/my-perf.fifo,/tmp/my-perf-ack.fifo,disabled
> >  --control /tmp/my-perf.fifo,,disabled
> > 
> > we already support this kind of options arguments, like for --call-graph
> > 
> > jirka
> > 
> 
> IMHO,
> this interface, of course, looks more compact (in amount of options) however
> the other side it is less user friendly. One simple option for one simple
> purpose is more convenient as for users as for developers. Also complex
> option syntax tends to have limitations and there are probably more
> non-obvious ones.
> 
> Please speak up. I might have missed something meaningful.

how about specify the type like:

--control fd:1,2,...
--control fifo:/tmp/fifo1,/tmp/fifo2
--control xxx:....

this way we can extend the functionality in the future
and stay backward compatible, while keeping single option

jirka