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

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Message-ID: <37D7C6CF3E00A74B8858931C1DB2F07753800042@SHSMSX103.ccr.corp.intel.com>
Date:   Fri, 12 Jan 2018 16:46:14 +0000
From:   "Liang, Kan" <kan.liang@...el.com>
To:     Jiri Olsa <jolsa@...hat.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
> >
> 
> The rules for perf_top_overwrite_check is quite simple.
>  - All events have same per-event mode.
>    E.g. "cpu/cpu-cycles,no-overwrite/,cpu/instructions,no-overwrite/
>    Using the per-event setting to replace the opts->overwrite if they are
> different.
>  - Events have different per-event mode.
>    E.g. "cpu/cpu-cycles,overwrite/,cpu/instructions,no-overwrite/"
>    Error out.
>  - Some of the event set per-event mode, but some not.
>    E.g. "cpu/cpu-cycles, /,cpu/instructions,no-overwrite/"
>    Error out.
> 
> There is no --overwrite option support for perf top.
> We have a default opts->overwrite.
> In perf_evlist__config, attr->write_backward will be set according to
> opts->overwrite at first. But if there is per-event mode, the
> attr->write_backward will be updated accordingly.
> There may be inconsistent between opts->overwrite and
> attr->write_backward.
> 
> perf_top_overwrite_check will be called right after perf_evlist__config.
> It can fix the inconsistence by updating the opts->overwrite or error out.
> The opts->overwrite will be used by fallback and _mmap_read() later.
> 

Check the code again.
Perf_top_overwrite_check() reply on evsel->config_terms to check the
terms, which is already parsed before perf_evlist__config().
You are right, we can call it earlier.
I will move the codes right before the perf_evlist__config() in V4.

Thanks,
Kan