lkml.org 
[lkml]   [2009]   [Jul]   [5]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH 5/5] perf report: Support callchains with relative overhead rate
On Sun, Jul 05, 2009 at 10:34:00AM +0200, Ingo Molnar wrote:
>
> * Frederic Weisbecker <fweisbec@gmail.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!



Ok.

I first planned to add a submode, or more likely a parameter structured
like the following:

perf report -c layout,min,mode

where layout=flat|graph
and mode=abs|rel
But relative flat doesn't make sense.
fractal is nice, it's just a pity that "graph" mode doesn't tell much
about it's absolute measure context.

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



\
 
 \ /
  Last update: 2009-07-05 15:23    [from the cache]
©2003-2011 Jasper Spaans