Date: Tue, 26 Apr 2016 23:55:36 +0200
From: Peter Zijlstra <peterz@infradead.org>
To: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Brendan Gregg <brendan.d.gregg@gmail.com>,
        Arnaldo Carvalho de Melo <arnaldo.melo@gmail.com>,
        Alexei Starovoitov <alexei.starovoitov@gmail.com>,
        David Ahern <dsahern@gmail.com>,
        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>
Subject: Re: [PATCH/RFC v3] perf core: Allow setting up max frame stack depth
 via sysctl
Message-ID: <20160426215536.GP3430@twins.programming.kicks-ass.net>
References: <20160425201750.GD25218@kernel.org>
 <20160425215947.GA25915@ast-mbp.thefacebook.com>
 <20160425234138.GA16708@kernel.org>
 <20160426000724.GA28705@ast-mbp.thefacebook.com>
 <20160426002928.GB16708@kernel.org>
 <20160426004358.GA29875@ast-mbp.thefacebook.com>
 <20160426004747.GC16708@kernel.org>
 <CAE40pdeG-TrtBNS10XDQx2ynFqRAhbgENrU7g-_3Oqho047E0A@mail.gmail.com>
 <CAE40pddVQPk+O5X=RcqgyYWY06pJMO+hBf7DjC0ugyZJaMRp_w@mail.gmail.com>
 <20160426210500.GK11033@kernel.org>
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On Tue, Apr 26, 2016 at 06:05:00PM -0300, Arnaldo Carvalho de Melo wrote:
> > I started with max depth = 512, and even that was still truncated, and
> > had to profile again at 1024 to capture the full stacks. Seems to

                           ^^^^^^

> > generally match the flame graph I generated with V1, which made me
> > want to check that I'm running the new patch, and am:
> > 
> > # grep six_hundred_forty_kb /proc/kallsyms
> > ffffffff81c431e0 d six_hundred_forty_kb
> > 
> > I was mucking around and was able to get "corrupted callchain.
> > skipping..." errors, but these look to be expected -- that was
> 
> Yeah, thanks for testing!
> 
> And since you talked about userspace without frame pointers, have you
> played with '--call-graph lbr'?

That seems to be at odds with his requirements; he needs 1024 entries to
capture full stacks, LBR is limited to 16/32 or so entries. That's 2
orders of magnitude difference.