From: Peter Zijlstra <peterz@infradead.org>
To: Andi Kleen <andi@firstfloor.org>
Cc: David Ahern <dsahern@gmail.com>,
Andy Lutomirski <luto@amacapital.net>,
Stephane Eranian <eranian@google.com>,
"Yan, Zheng" <zheng.z.yan@intel.com>,
LKML <linux-kernel@vger.kernel.org>,
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 22:15:40 +0100 [thread overview]
Message-ID: <20140226211540.GE22802@laptop.programming.kicks-ass.net> (raw)
In-Reply-To: <20140226205322.GM22728@two.firstfloor.org>
On Wed, Feb 26, 2014 at 09:53:22PM +0100, Andi Kleen wrote:
> > Is there some reason not to enable frame pointers?
>
> It makes code slower.
>
> Especially on Atom CPUs, where it causes pipeline stalls, but
Yeah, but nobody sane cares about the in-order atom crap CPUs.
> also to some degree on others, because you lose one register and
> spend a little bit of time setting it up, so making small
> functions more expensive.
Luckily GCC is rather good at inlining a lot of those. Esp. with LTO
like stuff.
> Another issue is that you can't enable it on a lot of existing
> libraries, sometimes not even with a recompile. For example
> glibc assembler functions do not support it at all, which
> is a very common case.
They're mostly all leaf functions, so it doesn't matter much if
anything.
> They are designed to use dwarf, but in practice dwarf
> is very slow (perf has to save the stack for every sample)
> and in practice doesn't always work (too small stack saving,
> wrong annotations, out of date or broken dwarf library etc.)
>
> LBR callstack mode is not perfect either, and it has
> its own tradeoffs, but in many cases it seems to be a good
> and more efficient replacement for dwarf, when FP is not available.
But except for the lobbying Intel put into disabling FP because of that
piece of shit Atom we'd all still have it enabled.
next prev parent reply other threads:[~2014-02-26 21:16 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 [this message]
2014-02-26 21:33 ` Andi Kleen
2014-02-26 21:34 ` David Ahern
2014-02-26 21:42 ` Andi Kleen
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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