linux-kernel - Re: [PATCH 01/14] perf/x86: Introduce PERF_RECORD

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Date:   Thu, 24 Nov 2016 15:27:47 +0100
From:   Jiri Olsa <jolsa@...hat.com>
To:     "Liang, Kan" <kan.liang@...el.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "acme@...nel.org" <acme@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "alexander.shishkin@...ux.intel.com" 
        <alexander.shishkin@...ux.intel.com>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "namhyung@...nel.org" <namhyung@...nel.org>,
        "jolsa@...nel.org" <jolsa@...nel.org>,
        "Hunter, Adrian" <adrian.hunter@...el.com>,
        "wangnan0@...wei.com" <wangnan0@...wei.com>,
        "mark.rutland@....com" <mark.rutland@....com>,
        "andi@...stfloor.org" <andi@...stfloor.org>
Subject: Re: [PATCH 01/14] perf/x86: Introduce PERF_RECORD_OVERHEAD

On Thu, Nov 24, 2016 at 01:56:51PM +0000, Liang, Kan wrote:
> 
> 
> > 
> > On Thu, Nov 24, 2016 at 01:45:28PM +0000, Liang, Kan wrote:
> > > > I think we should make this optional/configurable like the rest of
> > > > the aux events, like below..
> > > >
> > >
> > > The overhead logging only happens when event is going to be disabled
> > > or the task is scheduling out. It should not be much and expensive.
> > >
> > > Peter,
> > >
> > > What do you think?
> > > Should we make it configurable?
> > 
> > Is there a downside to having it optional?
> 
> NO. There will be no overhead information dumped into perf.data. Just like
> current implementation.

old perf tools will get unexpected events if it's not optional

[root@...-x3650m4-01 perf]# ./perf c2c record -ag
^C[ perf record: Woken up 1 times to write data ]
Warning:
Found 1 unknown events!

Is this an older tool processing a perf.data file generated by a more recent tool?

If that is not the case, consider reporting to linux-kernel@...r.kernel.org.

[ perf record: Captured and wrote 2.333 MB perf.data (9370 samples) ]


jirka