linux-kernel - Re: [PATCH/RFC v3] perf core: Allow setting up max frame stack depth via sysctl

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Message-ID: <20160426004747.GC16708@kernel.org>
Date:	Mon, 25 Apr 2016 21:47:47 -0300
From:	Arnaldo Carvalho de Melo <acme@...nel.org>
To:	Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc:	Arnaldo Carvalho de Melo <arnaldo.melo@...il.com>,
	David Ahern <dsahern@...il.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Ingo Molnar <mingo@...nel.org>,
	Adrian Hunter <adrian.hunter@...el.com>,
	Brendan Gregg <brendan.d.gregg@...il.com>,
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
	Alexei Starovoitov <ast@...nel.org>,
	He Kuang <hekuang@...wei.com>, Jiri Olsa <jolsa@...hat.com>,
	Masami Hiramatsu <mhiramat@...nel.org>,
	Milian Wolff <milian.wolff@...b.com>,
	Namhyung Kim <namhyung@...nel.org>,
	Stephane Eranian <eranian@...gle.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Vince Weaver <vincent.weaver@...ne.edu>,
	Wang Nan <wangnan0@...wei.com>, Zefan Li <lizefan@...wei.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH/RFC v3] perf core: Allow setting up max frame stack depth
 via sysctl

Em Mon, Apr 25, 2016 at 05:44:00PM -0700, Alexei Starovoitov escreveu:
> On Mon, Apr 25, 2016 at 09:29:28PM -0300, Arnaldo Carvalho de Melo wrote:
> > Em Mon, Apr 25, 2016 at 05:07:26PM -0700, Alexei Starovoitov escreveu:
> > > > +	{
> > > > +		.procname	= "perf_event_max_stack",
> > > > +		.data		= NULL, /* filled in by handler */
> > > > +		.maxlen		= sizeof(sysctl_perf_event_max_stack),
> > > > +		.mode		= 0644,
> > > > +		.proc_handler	= perf_event_max_stack_handler,
> > > > +		.extra1		= &zero,
> > > > +	},
> >  
> > > you need to define a max value otherwise perf_callchain_entry__sizeof
> > > will overflow. Sure it's root only facility, but still not nice.
> > > 1M? Anything above 1M stack frames would be insane anyway.
> > > The rest looks good. Thanks!
> > 
> > Something else? ;-)
> 
> all looks good to me. Thanks a bunch!

Thanks for checking!
 
> >     Because we only allocate the callchain percpu data structures when there
> >     is a user, which allows for changing the max easily, its just a matter
> >     of having no callchain users at that point.
> >     
> >     Reported-and-Tested-by: Brendan Gregg <brendan.d.gregg@...il.com>
> >     Acked-by: Alexei Starovoitov <ast@...nel.org>
> 
> yep :)
> hopefully Brendan can give it another spin.

Agreed, and I'm calling it a day anyway, Brendan, please consider
retesting, thanks,

- Arnaldo