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

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Message-ID: <b04311d6-b1c6-d625-b227-9ae4f4370626@linux.intel.com>
Date:   Wed, 3 Jun 2020 15:01:43 +0300
From:   Alexey Budankov <alexey.budankov@...ux.intel.com>
To:     Adrian Hunter <adrian.hunter@...el.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

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.

Feel free to ask more.

~Alexey