linux-kernel - Re: [RFC 00/20] perf: Finish sampling commands when events are closed

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Message-ID: <20140812072947.GA1128@krava.brq.redhat.com>
Date:	Tue, 12 Aug 2014 09:29:47 +0200
From:	Jiri Olsa <jolsa@...hat.com>
To:	Arnaldo Carvalho de Melo <acme@...nel.org>
Cc:	Jiri Olsa <jolsa@...nel.org>, linux-kernel@...r.kernel.org,
	Adrian Hunter <adrian.hunter@...el.com>,
	Corey Ashford <cjashfor@...ux.vnet.ibm.com>,
	David Ahern <dsahern@...il.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Ingo Molnar <mingo@...nel.org>,
	Jean Pihet <jean.pihet@...aro.org>,
	Namhyung Kim <namhyung@...nel.org>,
	Paul Mackerras <paulus@...ba.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [RFC 00/20] perf: Finish sampling commands when events are closed

On Mon, Aug 11, 2014 at 05:12:49PM -0300, Arnaldo Carvalho de Melo wrote:
> Em Mon, Aug 11, 2014 at 10:49:54AM +0200, Jiri Olsa escreveu:
> > hi,
> > adding support to quit sampling commands:
> >   record,top,trace,kvm stat live
> > 
> > when all the monitored events are closed, like following perf
> > command will now exit when monitored process (pid 1234) exits:
> > 
> >   $ perf record -p 1234
> > 
> > I added independent poller object to handle basic polling
> > tasks. I had to factor some parts, so sending this as RFC,
> 
> Why? I'm trying to figure out why this poller class is needed, just from
> reading the changelog entries, no luck so far.

multiple reasons.. at the moment:
  - have a way to get FD state notification -> callback triggers for FD
    and we can figure when we are out of monitored events or notify there
    was error/hup on event

  - to be able to gather/register more kinds of FDs under one
    poll instance, so we could poll together on standard input
    or other kind of notify event with perf events within a
    single poll call

for future:
  - there's another feature for record to watch hotplug CPUs
    and open/close perf event for it when CPU is added/removed
    we need to watch/poll inotify events for that

  - when having multiple threads for record command we'll need to split
    evlist events into more polling instances, so each thread could
    poll independently

also I think the poller class just encapsulates the polling
processing and reduces the evlist complexity

jirka
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