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

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Date:   Thu, 24 Nov 2016 11:02:16 -0800
From:   Andi Kleen <andi@...stfloor.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Andi Kleen <andi@...stfloor.org>,
        "Liang, Kan" <kan.liang@...el.com>, Jiri Olsa <jolsa@...hat.com>,
        "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>
Subject: Re: [PATCH 01/14] perf/x86: Introduce PERF_RECORD_OVERHEAD

On Thu, Nov 24, 2016 at 07:58:49PM +0100, Peter Zijlstra wrote:
> On Thu, Nov 24, 2016 at 10:28:22AM -0800, Andi Kleen wrote:
> > On Thu, Nov 24, 2016 at 02:50:43PM +0100, Peter Zijlstra 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?
> > 
> > It would be good to always have at least one line overhead summary in the
> > default output. So if someone sends you a perf report output file and it has
> > suspicious overhead can investigate.
> 
> Sure, but that's a tool thing, totally irrelevant for the kernel.

It requires enabling the overhead records by default.

If there is really concern about not supporting old tool would need a
disable instead of an enable option.

-Andi