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

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Date:   Fri, 5 Jun 2020 18:23:17 +0300
From:   Alexey Budankov <alexey.budankov@...ux.intel.com>
To:     Jiri Olsa <jolsa@...hat.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 05.06.2020 17:47, Alexey Budankov wrote:
> 
> On 05.06.2020 16:57, Jiri Olsa wrote:
>> 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,...
> 
> What do these ... mean?

After all,
if you want it this way and it now also fits my needs I could convert
--ctl-fd[-ack] to --control fd:<ctl-fd>,<ack-fd> with use cases like
--control fd:<ctl-fd> and --control fd:<ctl-fd>,<ack-fd>. Accepted?

~Alexey

> 
>> --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
> 
> Well, it clarifies more. However it still implicitly assumes
> and requires proper ordering e.g. 1 is ctl-fd and 2 is ack-fd
> and if there are some more positions there will be gaps like
> --control fd:10,,something,,something ...
> 
> Why is one single option with complex syntax more preferable
> than several simple options? Also it would still consume almost
> equal amount of command line space in shell.
> 
> Thanks,
> Alexey
> 
>>
>> jirka
>>