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

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Message-ID: <20160426215536.GP3430@twins.programming.kicks-ass.net>
Date:	Tue, 26 Apr 2016 23:55:36 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Arnaldo Carvalho de Melo <acme@...nel.org>
Cc:	Brendan Gregg <brendan.d.gregg@...il.com>,
	Arnaldo Carvalho de Melo <arnaldo.melo@...il.com>,
	Alexei Starovoitov <alexei.starovoitov@...il.com>,
	David Ahern <dsahern@...il.com>,
	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 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.