linux-kernel - Re: [PATCH v7 01/13] tools/libperf: introduce notion of static polled file descriptors

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Date:   Mon, 15 Jun 2020 08:20:38 +0300
From:   Alexey Budankov <alexey.budankov@...ux.intel.com>
To:     Jiri Olsa <jolsa@...hat.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 v7 01/13] tools/libperf: introduce notion of static polled
 file descriptors


On 08.06.2020 19:07, Jiri Olsa wrote:
> On Mon, Jun 08, 2020 at 12:54:31PM +0300, Alexey Budankov wrote:
>>
>> On 08.06.2020 11:43, Jiri Olsa wrote:
>>> On Mon, Jun 08, 2020 at 11:08:56AM +0300, Alexey Budankov wrote:
>>>>
>>>> On 05.06.2020 19:15, Alexey Budankov wrote:
>>>>>
>>>>> On 05.06.2020 14:38, Jiri Olsa wrote:
<SNIP>
>>>>> revents = fdarray_fixed_revents(array, pos);
>>>>> fdarray__del(array, pos);
>>>>
>>>> So how is it about just adding _revents() and _del() for fixed fds with
>>>> correction of retval to bool for fdarray__add()?
>>>
>>> I don't like the separation for fixed and non-fixed fds,
>>> why can't we make generic?
>>
>> Usage models are different but they want still to be parts of the same class
>> for atomic poll(). The distinction is filterable vs. not filterable.
>> The distinction should be somehow provided in API. Options are:
>> 1. expose separate API calls like __add_nonfilterable(), __del_nonfilterable();
>>    use nonfilterable quality in __filter() and __poll() and, perhaps, other internals;
>> 2. extend fdarray__add(, nonfilterable) with the nonfilterable quality
>>    use the type in __filter() and __poll() and, perhaps, other internals;
>>    expose less API calls in comparison with option 1
>>
>> Exposure of pos for filterable fds should be converted to bool since currently
>> the returned pos can become stale and there is no way in API to check its state.
>> So it could look like this:
>>
>> fdkey = fdarray__add(array, fd, events, type)
>> type: filterable, nonfilterable, somthing else
>> revents = fdarray__get_revents(fdkey);
>> fdarray__del(array, fdkey);
> 
> I think there's solution without having filterable type,
> I'm not sure why you think this is needed
> 
> I'm busy with other things this week, but I think I can
> come up with some patch early next week if needed

Friendly reminder.

Thanks,
Alexey