linux-kernel - Re: [PATCH] perf tool: Round mmap pages to power 2

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Date:	Mon, 11 Nov 2013 09:55:45 +0200
From:	Adrian Hunter <adrian.hunter@...el.com>
To:	David Ahern <dsahern@...il.com>
CC:	acme@...stprotocols.net, linux-kernel@...r.kernel.org,
	Ingo Molnar <mingo@...nel.org>, Jiri Olsa <jolsa@...hat.com>
Subject: Re: [PATCH] perf tool: Round mmap pages to power 2

On 08/11/13 16:41, David Ahern wrote:
> On 11/8/13, 2:11 AM, Adrian Hunter wrote:
>> This prevents:
>>
>>      --out-pages=0
>>
>> from working e.g.
>>
>>      tools/perf/perf record -vv --out-pages=0 uname
>>      rounding mmap pages size to 4096 (1 pages)
>>
>> Although without this patch:
>>
>>      tools/perf/perf record -vv --out-pages=0 uname
>>      --mmap_pages/-m value must be a power of two.
>>       usage: perf record [<options>] [<command>]
>>          or: perf record [<options>] -- <command> [<options>]
>>
>>              --out-pages <pages>
>>                            Number of pages or size with units to use for
>> output (default 64M)
>>
>> Also there is:
>>
>>      tools/perf/perf record -vv --no-out-pages uname
>>      Segmentation fault (core dumped)
>
> This is problem with perf_evlist__parse_mmap_pages(); same thing happens
> with --no-map-pages.
>
> With the attached both round a 0 up to 1 page:
>
> [daahern@...s-vdc-dev3 perf]$ perf record --out-pages 0 uname
> rounding mmap pages size to 4096 (1 pages)


Your code looks like out_pages = 0 selects write() instead of mmap().
So it you can't set out_pages = 0, how do you select write()?


> Linux
> [ perf record: Woken up 1 times to write data ]
> [ perf record: Captured and wrote 0.008 MB perf.data (~339 samples) ]
>
> [daahern@...s-vdc-dev3 perf]$ perf record --mmap-pages 0 uname
> rounding mmap pages size to 4096 (1 pages)
> Linux
> [ perf record: Woken up 1 times to write data ]
> [ perf record: Captured and wrote 0.008 MB perf.data (~339 samples) ]
>
> [daahern@...s-vdc-dev3 perf]$ perf record --no-mmap-pages uname
>
>  usage: perf record [<options>] [<command>]
>     or: perf record [<options>] -- <command> [<options>]
>
>     -m, --mmap-pages <pages>
>                           number of mmap data pages
> David
>

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