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

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Message-ID: <eb31a2a4-ab3b-54a7-2d5a-51457f78394e@intel.com>
Date:   Wed, 3 Jun 2020 15:23:53 +0300
From:   Adrian Hunter <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

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.