linux-kernel - Re: [PATCH 14/42] perf record: Add --index option for building index table

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Date:	Tue, 03 Feb 2015 10:42:33 +0200
From:	Adrian Hunter <adrian.hunter@...el.com>
To:	Jiri Olsa <jolsa@...hat.com>, Namhyung Kim <namhyung@...nel.org>
CC:	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	LKML <linux-kernel@...r.kernel.org>,
	David Ahern <dsahern@...il.com>,
	Andi Kleen <andi@...stfloor.org>,
	Stephane Eranian <eranian@...gle.com>,
	Frederic Weisbecker <fweisbec@...il.com>
Subject: Re: [PATCH 14/42] perf record: Add --index option for building index
 table

On 02/02/15 19:30, Jiri Olsa wrote:
> On Mon, Feb 02, 2015 at 11:56:09PM +0900, Namhyung Kim wrote:
>> Hi Jiri and Adrian,
>>
>> On Mon, Feb 2, 2015 at 9:13 PM, Jiri Olsa <jolsa@...hat.com> wrote:
>>> On Mon, Feb 02, 2015 at 02:07:27PM +0200, Adrian Hunter wrote:
>>>
>>> SNIP
>>>
>>>>>>
>>>>>> Why not make it the same as all the other data. i.e. find the start and size
>>>>>> via the index? And then just lump all the data together?
>>>>>
>>>>> thats what I suggested
>>>>
>>>> No, I meant really lump it all together. i.e. perf_file_header.data.size =
>>>> total data size
>>>>
>>>>>
>>>>>>
>>>>>>> I guess we could workaround that by storing the 'perf_file_header::data'
>>>>>>> as the last data section. That would require to treat it the same way as
>>>>>>> all other data sections, but we could keep current header layout.
>>>>>>
>>>>>> Would it need to be last? Logically it should precede the data that depends
>>>>>> on it.
>>>>>
>>>>> i suggested this as a workaround for having features at the end of the file
>>>>> while keeping the current perf data header
>>>>
>>>> Which wouldn't be necessary if you lump it all together?
>>>
>>> yep, that's also an option
>>
>> So we want a single section for the entire data area, right?
>>
>> I also thought about it.  My concern was the holes between each data
>> due to page alignment.  If an old tool which doesn't know about the
>> index accesses to the data file, it'd just see a event type of 0 and
>> stop processing.

Please don't leave holes. Either fill them with a padding event or put the
data end-to-end.

>>
>> Maybe the page alignment is not necessary?
> 
> seems ok,  but how about time ordering.. every time you reach new
> file data you'll hit 'out of order event' right?
> 
> hum, maybe it's not a big deal now when it's just incrementing counter ;-)
> 
> jirka
> 
> 

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