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

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Date:	Mon, 25 Apr 2016 17:49:38 -0700
From:	Brendan Gregg <brendan.d.gregg@...il.com>
To:	Arnaldo Carvalho de Melo <arnaldo.melo@...il.com>
Cc:	Alexei Starovoitov <alexei.starovoitov@...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>,
	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

On Mon, Apr 25, 2016 at 5:47 PM, Arnaldo Carvalho de Melo
<arnaldo.melo@...il.com> wrote:
> 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,
>

Will do, thanks!

Brendan


> - Arnaldo