linux-kernel - Re: [PATCH V3 08/12] perf top: check per event overwrite term

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Date:   Fri, 12 Jan 2018 12:42:06 +0100
From:   Jiri Olsa <jolsa@...hat.com>
To:     "Liang, Kan" <kan.liang@...el.com>
Cc:     "acme@...nel.org" <acme@...nel.org>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "wangnan0@...wei.com" <wangnan0@...wei.com>,
        "jolsa@...nel.org" <jolsa@...nel.org>,
        "namhyung@...nel.org" <namhyung@...nel.org>,
        "ak@...ux.intel.com" <ak@...ux.intel.com>,
        "yao.jin@...ux.intel.com" <yao.jin@...ux.intel.com>
Subject: Re: [PATCH V3 08/12] perf top: check per event overwrite term

On Thu, Jan 11, 2018 at 09:29:21PM +0000, Liang, Kan wrote:
> > On Thu, Dec 21, 2017 at 10:08:50AM -0800, kan.liang@...el.com wrote:
> > > From: Kan Liang <kan.liang@...el.com>
> > >
> > > Per event overwrite term is not forbidden in perf top, which can bring
> > > problems. Because perf top only support non-overwrite mode.
> > >
> > > Check and forbid inconsistent per event overwrite term in the evlist.
> > > Make it possible to support either non-overwrite or overwrite mode.
> > > The overwrite mode is forbidden now, which will be removed when the
> > > overwrite mode is supported later.
> > >
> > > Signed-off-by: Kan Liang <kan.liang@...el.com>
> > > ---
> > >  tools/perf/builtin-top.c | 60
> > ++++++++++++++++++++++++++++++++++++++++++++++++
> > >  1 file changed, 60 insertions(+)
> > >
> > > diff --git a/tools/perf/builtin-top.c b/tools/perf/builtin-top.c
> > > index c6ccda5..4b85e7b 100644
> > > --- a/tools/perf/builtin-top.c
> > > +++ b/tools/perf/builtin-top.c
> > > @@ -881,6 +881,56 @@ static void perf_top__mmap_read(struct perf_top
> > *top)
> > >  		perf_top__mmap_read_idx(top, i);
> > >  }
> > >
> > > +/*
> > > + * Check per event overwrite term.
> > > + * perf top supports consistent mode for all events.
> > > + * Return -1 if the per event terms set but not consistent.
> > 
> > please list the rules for overwrite in the comment
> > are they just top specific?
> 
> Yes, it's only for perf top.
> It doesn't support that some events are overwrite mode and other events are
> non-overwrite mode.
> I will refine the comments.
> 
> > 
> > SNIP
> > 
> > > +			if (evsel == perf_evlist__first(evlist))
> > > +				overwrite = set;
> > > +			else
> > > +				return -1;
> > > +		}
> > > +	}
> > > +
> > > +	if ((overwrite >= 0) && (opts->overwrite != overwrite))
> > > +		opts->overwrite = overwrite;
> > > +
> > > +	return 0;
> > > +}
> > > +
> > >  static int perf_top__start_counters(struct perf_top *top)
> > >  {
> > >  	char msg[BUFSIZ];
> > > @@ -890,6 +940,16 @@ static int perf_top__start_counters(struct
> > perf_top *top)
> > >
> > >  	perf_evlist__config(evlist, opts, &callchain_param);
> > 
> > so perf_evlist__config uses opts->overwrite, which you set
> > in your perf_top_overwrite_check call.. I'd think you need
> > to call it sooner
> >
> 
> User may set per-event mode, which is processed in perf_evlist__config
> It's possible that the per-event mode is not same as opts->overwrite.
> If so, perf_evlist__config actually uses per-event mode.
> 
> perf_top_overwrite_check will do the check. If the per-event mode is
> inconsistent as opts->overwrite, updating the opts->overwrite.
> 
> It has to be called after the perf_evlist__config.

let's see the rules then first, also wrt opts->overwrite,
which is used later on I assume

thanks,
jirka