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From: Brendan Gregg <brendan.d.gregg@gmail.com>
Date: Mon, 25 Apr 2016 17:49:38 -0700
Message-ID: <CAE40pdeG-TrtBNS10XDQx2ynFqRAhbgENrU7g-_3Oqho047E0A@mail.gmail.com>
Subject: Re: [PATCH/RFC v3] perf core: Allow setting up max frame stack depth
 via sysctl
To: Arnaldo Carvalho de Melo <arnaldo.melo@gmail.com>
Cc: Alexei Starovoitov <alexei.starovoitov@gmail.com>,
        David Ahern <dsahern@gmail.com>, Peter Zijlstra <peterz@infradead.org>,
        Frederic Weisbecker <fweisbec@gmail.com>,
        Ingo Molnar <mingo@kernel.org>,
        Adrian Hunter <adrian.hunter@intel.com>,
        Alexander Shishkin <alexander.shishkin@linux.intel.com>,
        Alexei Starovoitov <ast@kernel.org>, He Kuang <hekuang@huawei.com>,
        Jiri Olsa <jolsa@redhat.com>, Masami Hiramatsu <mhiramat@kernel.org>,
        Milian Wolff <milian.wolff@kdab.com>,
        Namhyung Kim <namhyung@kernel.org>,
        Stephane Eranian <eranian@google.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Vince Weaver <vincent.weaver@maine.edu>,
        Wang Nan <wangnan0@huawei.com>, Zefan Li <lizefan@huawei.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
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On Mon, Apr 25, 2016 at 5:47 PM, Arnaldo Carvalho de Melo
<arnaldo.melo@gmail.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@gmail.com>
>> >     Acked-by: Alexei Starovoitov <ast@kernel.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