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

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Message-ID: <3ac6d0b8-5fae-348f-8556-4bf7a66285f6@linux.intel.com>
Date:   Fri, 5 Jun 2020 16:15:52 +0300
From:   Alexey Budankov <alexey.budankov@...ux.intel.com>
To:     Jiri Olsa <jolsa@...hat.com>,
        Adrian Hunter <adrian.hunter@...el.com>
Cc:     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 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.

~Alexey