linux-kernel - Re: buggy perf callgraph output

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Date:	Thu, 16 Dec 2010 00:02:45 +1100
From:	Nick Piggin <npiggin@...nel.dk>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	Nick Piggin <npiggin@...nel.dk>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	linux-kernel@...r.kernel.org
Subject: Re: buggy perf callgraph output

On Wed, Dec 08, 2010 at 10:48:13PM +0100, Frederic Weisbecker wrote:
> I can not reproduce it. Could you please try to reproduce,
> run perf archive and send me your perf.data.tar.bz2 ?

It seems to be happening all the time, just look further in
callgraphs.

This attached perf.data.bz2 looks like this, when using -g graph

    15.05%        dbench  [kernel.kallsyms]  [k]
copy_user_generic_string
                   |
                   --- copy_user_generic_string
                      |          
                      |---0.16%-- generic_file_aio_read
                      |          do_sync_read
                      |          vfs_read
                      |          |          
                      |           --0.05%-- sys_pread64
                      |                     system_call
                      |                     0x7f64a60bb193
                      |          
                      |--0.10%-- generic_file_buffered_write
                      |          __generic_file_aio_write
                      |          generic_file_aio_write
                      |          do_sync_write
                      |          vfs_write
                      |          sys_pwrite64
                      |          system_call
                      |          0x7f64a60bb203
                      |          0xe01170
                      |          
                       ---0.11%-- dcache_readdir
                                 vfs_readdir
                                 sys_getdents
                                 system_call
                                 0x7f64a60ade65

See, the last element is greater than the second last.

-g fractal looks like this:

    15.05%        dbench  [kernel.kallsyms]  [k]
copy_user_generic_string
                   |
                   --- copy_user_generic_string
                      |          
                      |---1.09%-- generic_file_aio_read
                      |          do_sync_read
                      |          vfs_read
                      |          |          
                      |          |--0.55%-- sys_pread64
                      |          |          system_call
                      |          |          0x7f64a60bb193
                      |          |          
                      |           --2.19%-- sys_read
                      |                     system_call
                      |                     0x7f64a60d3ea0
                      |          
                      |--0.69%-- generic_file_buffered_write
                      |          __generic_file_aio_write
                      |          generic_file_aio_write
                      |          do_sync_write
                      |          vfs_write
                      |          sys_pwrite64
                      |          system_call
                      |          0x7f64a60bb203
                      |          0xe01170
                      |          
                      |---0.72%-- dcache_readdir
                      |          vfs_readdir
                      |          sys_getdents
                      |          system_call
                      |          0x7f64a60ade65


So it's totally screwy.

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