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 14:30:48 +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 v7 01/13] tools/libperf: introduce notion of static
 polled file descriptors

On Mon, Jun 15, 2020 at 08:20:38AM +0300, Alexey Budankov wrote:
> 
> 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.

hm? I believe we discussed this in here:
  https://lore.kernel.org/lkml/20200609145611.GI1558310@krava/

jirka