linux-kernel - Re: [PATCH 03/10] perf record: Turns auxtrace_snapshot

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Date:	Thu, 14 Apr 2016 13:21:18 +0300
From:	Adrian Hunter <adrian.hunter@...el.com>
To:	"Wangnan (F)" <wangnan0@...wei.com>,
	Arnaldo Carvalho de Melo <acme@...nel.org>
Cc:	linux-kernel@...r.kernel.org, pi3orama@....com,
	He Kuang <hekuang@...wei.com>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Namhyung Kim <namhyung@...nel.org>,
	Zefan Li <lizefan@...wei.com>
Subject: Re: [PATCH 03/10] perf record: Turns auxtrace_snapshot_enable into 3
 states

On 14/04/16 12:07, Wangnan (F) wrote:
> 
> 
> On 2016/4/14 16:30, Adrian Hunter wrote:
>> On 14/04/16 10:50, Wangnan (F) wrote:
>>>
>>> On 2016/4/14 15:15, Adrian Hunter wrote:
>>>> On 13/04/16 18:55, Arnaldo Carvalho de Melo wrote:
>>>>> Em Wed, Apr 13, 2016 at 08:21:06AM +0000, Wang Nan escreveu:
>>>>>> auxtrace_snapshot_enable has only two states (0/1). Turns it into a
>>>>>> triple states enum so SIGUSR2 handler can safely do other works without
>>>>>> triggering auxtrace snapshot.
>>>>> Adrian, can you take a look at this? Is it ok with you?
>>>> Please forgive me if these are stupid questions:
>>>>
>>>> First I am wondering why we wouldn't want to snapshot auxtrace data at the
>>>> same time as the perf buffer?
>>> This patch doesn't prevent taking snapshot when receiving SIGUSR2.
>> So it was a stupid question ;-)
> 
> Still thank you for pointing this. I suddenly realized the
> 'switch_output_started'
> in patch 5/10 is also need to be turned to a 3 state enum. If not, a SIGUSR2
> incorrectly
> triggers output switching even '--switch-output' is not provided when
> '--snapshot' exist.
> 
>>
>>> If both --snapshot and --switch-outupt is provided, when SIGUSR2 received,
>>> perf takes auxtrace snapshot and other perf buffer together.
>> How do you keep from losing tracking information like MMAP events?  Are they
>> is a different buffer?
> 
> Please see patch 8/10 and 9/10. MMAP events are resynthesized each time
> when output file switched, so at the *head* of each 'perf.data' you can find
> many MMAP/COMM/FORK... events.

OK, I see.

> 
> After overwritable ring buffer is supported, there is a more aggresive
> patch [1] resynthesize tracking events and put them at the *end* of
> perf.data.
> 
> [1]
> https://git.kernel.org/cgit/linux/kernel/git/pi3orama/linux.git/commit/?h=perf/overwrite&id=747e10300397b9c28b01bca5bfad943c8cf2dcce
> 

Thanks for the information.  Auxtrace really needs complete MMAP
information, so I would probably need to look at other options as well.

Anyway for this patch:

Acked-by: Adrian Hunter <adrian.hunter@...el.com>