linux-kernel - Re: [PATCH 5/5] perf report: Support callchains with relative overhead rate

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Message-ID: <20090705083400.GB12783@elte.hu>
Date:	Sun, 5 Jul 2009 10:34:00 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Mike Galbraith <efault@....de>,
	Paul Mackerras <paulus@...ba.org>,
	Anton Blanchard <anton@...ba.org>,
	Jens Axboe <jens.axboe@...cle.com>,
	Arnaldo Carvalho de Melo <acme@...hat.com>
Subject: Re: [PATCH 5/5] perf report: Support callchains with relative
	overhead rate


* Frederic Weisbecker <fweisbec@...il.com> wrote:

> The current callchain displays the overhead rates as absolute:
> relative to the total overhead.
> 
> This patch provides relative overhead percentage, in which each
> branch of the callchain tree is a independant instrumentated object.
> 
> You can produce such output by using the "relative" mode
> that you can lower in r, re, rel, etc...
> 
> ./perf report -s sym -c relative
> 
> Example:
> 
>      8.46%  [k] copy_user_generic_string
>                 |
>                 |--52.01%-- generic_file_aio_read
>                 |          do_sync_read
>                 |          vfs_read
>                 |          |
>                 |          |--97.20%-- sys_pread64
>                 |          |          system_call_fastpath
>                 |          |          pread64
>                 |          |
>                 |           --2.81%-- sys_read
>                 |                     system_call_fastpath
>                 |                     __read
>                 |
>                 |--39.85%-- generic_file_buffered_write
>                 |          __generic_file_aio_write_nolock
>                 |          generic_file_aio_write
>                 |          do_sync_write
>                 |          reiserfs_file_write
>                 |          vfs_write
>                 |          |
>                 |          |--97.05%-- sys_pwrite64
>                 |          |          system_call_fastpath
>                 |          |          __pwrite64
>                 |          |
>                 |           --2.95%-- sys_write
>                 |                     system_call_fastpath
>                 |                     __write_nocancel
> [...]

Wow, this is extremely intuitive and powerful looking!

It's basically a fractal structure: each sub-graph looks like a 
full-blown profile in itself. Thus the overhead of individual 
components of the graph profile can be analyzed without having to 
think in small numbers.

The above example shows it particularly well - it shows that in 
regard to generic_file_buffered_write() overhead, the system is 
doing 97% sys_pwrite64() calls and 3% sys_write() calls.

Thus i took the liberty to change your last patch in two ways: i 
renamed 'relative' to 'fractal' (it was not a proper counterpart to 
'graph' anyway - we have no 'absolute' output mode name either), and 
i changed it to be the default output mode. This stuff rocks!

absolute-graph and flat mode can be displayed too, via the option, 
as usual.

	Ingo
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