linux-kernel - Re: [PATCH 0/5] perf: add two new features

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Date:	Wed, 17 Jul 2013 14:28:47 +0300
From:	Adrian Hunter <adrian.hunter@...el.com>
To:	Peter Zijlstra <peterz@...radead.org>
CC:	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	H Peter Anvin <hpa@...or.com>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	David Ahern <dsahern@...il.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Jiri Olsa <jolsa@...hat.com>, Mike Galbraith <efault@....de>,
	Namhyung Kim <namhyung@...il.com>,
	Paul Mackerras <paulus@...ba.org>,
	Stephane Eranian <eranian@...gle.com>
Subject: Re: [PATCH 0/5] perf: add two new features

On 16/07/13 17:34, Peter Zijlstra wrote:
> On Tue, Jul 16, 2013 at 09:22:00AM +0300, Adrian Hunter wrote:
>> On 28/06/13 22:22, Adrian Hunter wrote:
>>> On 28/06/2013 6:27 p.m., Peter Zijlstra wrote:
>>>> On Fri, Jun 28, 2013 at 04:22:16PM +0300, Adrian Hunter wrote:
>>>>> Hi
>>>>>
>>>>> Please consider these two new perf features:
>>>>>        x86: add ability to calculate TSC from perf sample timestamps
>>>>>        perf: add 'keep tracking' flag to PERF_EVENT_IOC_DISABLE
>>>>
>>>> Please explain to us why you'd like to do this..
>>>
>>> I will see what information I can dig up.  The short answer is that I need
>>> to disable and re-enable a perf event but still be able to map IPs to their
>>> DSOs and symbols - which means not losing mmap events.
>>
>> Any other comments?
> 
> Ah, thanks for the reminder.. well, I've applied patches 1-3 as those seem
> useful on their own. I'm not entirely convinced about the 'keep tracking' thing
> though.
> 
> It seems to me you could get the same by opening a second event into the same
> buffer and keeping that enabled.

In that case I would like a dummy event to use for that purpose.  A software
event could be set aside e.g.

diff --git a/include/uapi/linux/perf_event.h b/include/uapi/linux/perf_event.h
index 627bbcf..7ea4ccd 100644
--- a/include/uapi/linux/perf_event.h
+++ b/include/uapi/linux/perf_event.h
@@ -109,6 +109,7 @@ enum perf_sw_ids {
        PERF_COUNT_SW_PAGE_FAULTS_MAJ           = 6,
        PERF_COUNT_SW_ALIGNMENT_FAULTS          = 7,
        PERF_COUNT_SW_EMULATION_FAULTS          = 8,
+       PERF_COUNT_SW_DUMMY                     = 9,

        PERF_COUNT_SW_MAX,                      /* non-ABI */
 };


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