From: Andi Kleen <andi@firstfloor.org>
To: David Ahern <dsahern@gmail.com>
Cc: Andi Kleen <andi@firstfloor.org>,
Andy Lutomirski <luto@amacapital.net>,
Stephane Eranian <eranian@google.com>,
"Yan, Zheng" <zheng.z.yan@intel.com>,
LKML <linux-kernel@vger.kernel.org>,
Peter Zijlstra <a.p.zijlstra@chello.nl>,
Ingo Molnar <mingo@kernel.org>,
Arnaldo Carvalho de Melo <acme@infradead.org>
Subject: Re: [PATCH v3 00/14] perf, x86: Haswell LBR call stack support
Date: Wed, 26 Feb 2014 22:42:36 +0100 [thread overview]
Message-ID: <20140226214236.GO22728@two.firstfloor.org> (raw)
In-Reply-To: <530E5DE7.7060904@gmail.com>
On Wed, Feb 26, 2014 at 02:34:31PM -0700, David Ahern wrote:
> On 2/26/14, 1:53 PM, Andi Kleen wrote:
> >>Is there some reason not to enable frame pointers?
> >
> >It makes code slower.
>
> Sure there is some overhead because of the push, mov, pop
> instructions per function. But, take for example the simple program
> below. Compile with and without frame pointers
I'm not criticizing your choice, just saying that
it's often not practical to get FP everywhere
(and I bet you missed some cases too)
<.. micro benchmark snipped...>
The CPU you're using has special hardware to avoid the main
problems with FP. It can still cause slow downs in other
cases (e.g. one register less). But there are other
CPUs where this special hardware is not available.
You may not care about these cases, but other people do.
> >wrong annotations, out of date or broken dwarf library etc.)
>
> dwarf is often just not usable:
I agree (altough I haven't seen that error before)
> That is a huge difference. Not to mention the fact the dwarf file is
> useless which means radically lowering sample rate and increasing
> mmap size.
Yep.
It's just fundamentally inefficient for profiling.
-Andi
next prev parent reply other threads:[~2014-02-26 21:42 UTC|newest]
Thread overview: 40+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-02-18 6:07 [PATCH v3 00/14] perf, x86: Haswell LBR call stack support Yan, Zheng
2014-02-18 6:07 ` [PATCH v3 01/14] perf, x86: Reduce lbr_sel_map size Yan, Zheng
2014-02-18 6:07 ` [PATCH v3 02/14] perf, core: introduce pmu context switch callback Yan, Zheng
2014-02-18 6:07 ` [PATCH v3 03/14] perf, x86: use context switch callback to flush LBR stack Yan, Zheng
2014-02-18 6:07 ` [PATCH v3 04/14] perf, x86: Basic Haswell LBR call stack support Yan, Zheng
2014-02-18 6:07 ` [PATCH v3 05/14] perf, core: pmu specific data for perf task context Yan, Zheng
2014-02-18 6:07 ` [PATCH v3 06/14] perf, core: always switch pmu specific data during context switch Yan, Zheng
2014-02-18 6:07 ` [PATCH v3 07/14] perf, x86: track number of events that use LBR callstack Yan, Zheng
2014-02-18 6:07 ` [PATCH v3 08/14] perf, x86: allocate space for storing LBR stack Yan, Zheng
2014-02-18 6:07 ` [PATCH v3 09/14] perf, x86: Save/resotre LBR stack during context switch Yan, Zheng
2014-02-18 6:07 ` [PATCH v3 10/14] perf, core: simplify need branch stack check Yan, Zheng
2014-02-18 6:07 ` [PATCH v3 11/14] perf, core: Pass perf_sample_data to perf_callchain() Yan, Zheng
2014-02-18 6:07 ` [PATCH v3 12/14] perf, x86: use LBR call stack to get user callchain Yan, Zheng
2014-02-18 6:07 ` [PATCH v3 13/14] perf, x86: enable LBR callstack when recording callchain Yan, Zheng
2014-02-18 6:07 ` [PATCH v3 14/14] perf, x86: Discard zero length call entries in LBR call stack Yan, Zheng
2014-02-23 19:47 ` [PATCH v3 00/14] perf, x86: Haswell LBR call stack support Stephane Eranian
2014-02-24 1:07 ` Yan, Zheng
2014-02-24 7:14 ` Peter Zijlstra
2014-02-26 2:39 ` Andy Lutomirski
2014-02-26 7:04 ` Stephane Eranian
2014-02-26 8:57 ` Yan, Zheng
2014-02-26 16:03 ` Andy Lutomirski
2014-02-26 18:55 ` Andi Kleen
2014-02-26 18:59 ` Andy Lutomirski
2014-02-26 19:19 ` David Ahern
2014-02-26 19:25 ` Andy Lutomirski
2014-02-26 20:14 ` David Ahern
2014-02-26 20:26 ` Andy Lutomirski
2014-04-09 11:48 ` Peter Zijlstra
2014-04-09 16:48 ` Andi Kleen
2014-04-09 17:40 ` Andi Kleen
2014-02-26 20:32 ` Peter Zijlstra
2014-02-26 20:53 ` Andi Kleen
2014-02-26 21:15 ` Peter Zijlstra
2014-02-26 21:33 ` Andi Kleen
2014-02-26 21:34 ` David Ahern
2014-02-26 21:42 ` Andi Kleen [this message]
2014-02-27 9:09 ` Stephane Eranian
2014-02-27 12:35 ` Ingo Molnar
2014-02-27 16:08 ` Andi Kleen
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