linux-kernel - RE: [PATCH v6 01/13] tools/libperf: introduce notion of static polled file descriptors

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Message-ID: <363DA0ED52042842948283D2FC38E464B4151F86@IRSMSX106.ger.corp.intel.com>
Date:   Wed, 3 Jun 2020 12:30:15 +0000
From:   "Hunter, Adrian" <adrian.hunter@...el.com>
To:     Alexey Budankov <alexey.budankov@...ux.intel.com>
CC:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        Jiri Olsa <jolsa@...hat.com>,
        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 v6 01/13] tools/libperf: introduce notion of static
 polled file descriptors



> -----Original Message-----
> From: Hunter, Adrian <adrian.hunter@...el.com>
> Sent: Wednesday, June 3, 2020 3:24 PM
> To: Alexey Budankov <alexey.budankov@...ux.intel.com>
> Cc: Arnaldo Carvalho de Melo <acme@...nel.org>; Jiri Olsa
> <jolsa@...hat.com>; 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 v6 01/13] tools/libperf: introduce notion of static polled
> file descriptors
> 
> On 3/06/20 3:01 pm, Alexey Budankov wrote:
> > Hi,
> >
> > On 03.06.2020 14:38, Adrian Hunter wrote:
> >> On 1/06/20 11:05 pm, Alexey Budankov wrote:
> >>>
> >>> Implement adding of file descriptors by fdarray__add_stat() to
> >>> fix-sized (currently 1) stat_entries array located at struct fdarray.
> >>> Append added file descriptors to the array used by poll() syscall
> >>> during fdarray__poll() call. Copy poll() result of the added
> >>> descriptors from the array back to the storage for separate analysis.
> >>
> >> Why not instead call evlist__add_pollfd() before other fds are added,
> >> so the fda->entries[] position is always fixed. Then this patch is not
> needed.
> >
> > It then will block event consumption loop, at least in record mode,
> > due to change sin initial assumptions behind fdarray__filter(). So
> > extension of the API with 'static' fds looks safer w.r.t. possible
> > functional regressions at the same time extending the API with ability
> > to atomically wait for (poll()) not only event fds but also any other fds
> during monitoring.
> 
> So make fdarray__filter() return the number of filterable fds remaining.
> 


Or perhaps simpler, compare the return value to the number of fds that are known not to be filterable