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From: Andi Kleen <andi@firstfloor.org>
To: "Yan, Zheng" <zheng.z.yan@intel.com>
Cc: linux-kernel@vger.kernel.org, a.p.zijlstra@chello.nl,
	mingo@kernel.org, acme@infradead.org, eranian@google.com,
	andi@firstfloor.org
Subject: Re: [PATCH V4 14/16] perf, x86: enable LBR callstack when recording callchain
Date: Mon, 30 Jun 2014 16:45:16 +0200	[thread overview]
Message-ID: <20140630144516.GJ5714@two.firstfloor.org> (raw)
In-Reply-To: <1404118253-19532-15-git-send-email-zheng.z.yan@intel.com>

On Mon, Jun 30, 2014 at 04:50:51PM +0800, Yan, Zheng wrote:
> If a task specific event wants user space callchain but does not want
> branch stack sampling, enable the LBR call stack facility implicitly.
> The LBR call stack facility can help perf to get user space callchain
> in case of there is no frame pointer.
> 
> Note: this feature only affects how to get user callchain. The kernel
> callchain is always got by frame pointers.

I'm not sure I like this. If frame pointer works the LBR state saving
is not needed. This would basically always turn it on right?

Perhaps turn it on lazily if the frame pointer resolution fails a few
times.

An explicit switch would be still better.

-Andi

  reply	other threads:[~2014-06-30 14:45 UTC|newest]

Thread overview: 37+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2014-06-30  8:50 [PATCH V4 00/16] perf, x86: Haswell LBR call stack support Yan, Zheng
2014-06-30  8:50 ` [PATCH V4 01/16] perf, x86: Reduce lbr_sel_map size Yan, Zheng
2014-06-30  8:50 ` [PATCH V4 02/16] perf, core: introduce pmu context switch callback Yan, Zheng
2014-07-02  8:48   ` Peter Zijlstra
2014-07-02 10:12   ` Peter Zijlstra
2014-07-03  5:47     ` Yan, Zheng
2014-06-30  8:50 ` [PATCH V4 03/16] perf, x86: use context switch callback to flush LBR stack Yan, Zheng
2014-07-02  9:06   ` Peter Zijlstra
2014-07-03  5:44     ` Yan, Zheng
2014-06-30  8:50 ` [PATCH V4 04/16] perf, x86: Basic Haswell LBR call stack support Yan, Zheng
2014-07-02 10:14   ` Peter Zijlstra
2014-06-30  8:50 ` [PATCH V4 05/16] perf, core: pmu specific data for perf task context Yan, Zheng
2014-07-02 10:18   ` Peter Zijlstra
2014-06-30  8:50 ` [PATCH V4 06/16] perf, core: always switch pmu specific data during context switch Yan, Zheng
2014-07-02 10:19   ` Peter Zijlstra
2014-06-30  8:50 ` [PATCH V4 07/16] perf, x86: track number of events that use LBR callstack Yan, Zheng
2014-07-02 10:21   ` Peter Zijlstra
2014-07-03  5:59     ` Yan, Zheng
2014-07-02 10:25   ` Peter Zijlstra
2014-06-30  8:50 ` [PATCH V4 08/16] perf, x86: allocate space for storing LBR stack Yan, Zheng
2014-06-30  8:50 ` [PATCH V4 09/16] perf, x86: Save/resotre LBR stack during context switch Yan, Zheng
2014-07-02 10:49   ` Peter Zijlstra
2014-06-30  8:50 ` [PATCH V4 10/16] perf, core: simplify need branch stack check Yan, Zheng
2014-07-02 10:57   ` Peter Zijlstra
2014-07-02 11:08     ` Stephane Eranian
2014-07-02 12:27       ` Peter Zijlstra
2014-07-02 13:00         ` Stephane Eranian
2014-07-02 13:28           ` Peter Zijlstra
2014-06-30  8:50 ` [PATCH V4 11/16] perf, core: Pass perf_sample_data to perf_callchain() Yan, Zheng
2014-06-30  8:50 ` [PATCH V4 12/16] perf, x86: use LBR call stack to get user callchain Yan, Zheng
2014-06-30  8:50 ` [PATCH V4 13/16] perf, x86: re-organize code that implicitly enables LBR/PEBS Yan, Zheng
2014-06-30  8:50 ` [PATCH V4 14/16] perf, x86: enable LBR callstack when recording callchain Yan, Zheng
2014-06-30 14:45   ` Andi Kleen [this message]
2014-06-30  8:50 ` [PATCH V4 15/16] perf, x86: disable FREEZE_LBRS_ON_PMI when LBR operates in callstack mode Yan, Zheng
2014-07-02 11:13   ` Peter Zijlstra
2014-06-30  8:50 ` [PATCH V4 16/16] perf, x86: Discard zero length call entries in LBR call stack Yan, Zheng
  -- strict thread matches above, loose matches on Subject: below --
2014-03-17  5:57 [PATCH v4 00/16] perf, x86: Haswell LBR call stack support Yan, Zheng
2014-03-17  5:57 ` [PATCH v4 14/16] perf, x86: enable LBR callstack when recording callchain Yan, Zheng

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