linux-kernel - Re: [PATCH 2/5] perf unwind: Do not look at globals

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Message-ID: <20180117082307.GE6183@krava>
Date:   Wed, 17 Jan 2018 09:23:07 +0100
From:   Jiri Olsa <jolsa@...hat.com>
To:     Arnaldo Carvalho de Melo <acme@...nel.org>
Cc:     Jiri Olsa <jolsa@...nel.org>, Ingo Molnar <mingo@...nel.org>,
        linux-kernel@...r.kernel.org, linux-perf-users@...r.kernel.org,
        Arnaldo Carvalho de Melo <acme@...hat.com>,
        Adrian Hunter <adrian.hunter@...el.com>,
        David Ahern <dsahern@...il.com>,
        Hendrick Brueckner <brueckner@...ux.vnet.ibm.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Thomas Richter <tmricht@...ux.vnet.ibm.com>,
        Wang Nan <wangnan0@...wei.com>
Subject: Re: [PATCH 2/5] perf unwind: Do not look at globals

On Tue, Jan 16, 2018 at 05:05:20PM -0300, Arnaldo Carvalho de Melo wrote:

SNIP

> > >  
> > > +/*
> > > + * Are there any events usind DWARF callchains?
> > > + *
> > > + * I.e.
> > > + *
> > > + * -e cycles/call-graph=dwarf/
> > > + */
> > > +bool dwarf_callchain_users;
> > 
> > hum, I don't follow.. this bool seems to mirror the usage of
> > 'param->record_mode = CALLCHAIN_DWARF', whats the difference?
> > 
> > also, the patch title says 'Do not look at globals', while inside you
> 
> The first version didn't look at globals, the second one doesn't look at
> an _specific_ global variable, the global config for --call-graph, which
> is a global variable, callchain_param, which _we_ can't touch at
> apply_config_terms(), since that is about _just_ that event, not all of
> them.
> 
> > add new global dwarf_callchain_users and work with it.. what do I miss?
> > 
> > I'll check tomorrow with clean head ;-)
> 
> Look closely at apply_config_terms() it passes a _local_ variable to
> 
>                         perf_evsel__config_callchain(evsel, opts, &param);
> 
> It will not affect any globals that tools/perf/util/unwind-libunwind-local.c
> could possibly use... and that is the problem. :-)

ah ok, that one is local.. just to set up the attrs

then adding that new variable is ok, though it could be
aded inside struct callchain_param, to keep callchain
config stuff together

thanks,
jirka