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Date: Thu, 16 Dec 2010 12:47:58 +0100
From: Frederic Weisbecker <fweisbec@...il.com>
To: Nick Piggin <npiggin@...nel.dk>
Cc: Arnaldo Carvalho de Melo <acme@...hat.com>,
linux-kernel@...r.kernel.org
Subject: Re: buggy perf callgraph output
On Thu, Dec 16, 2010 at 12:02:45AM +1100, Nick Piggin wrote:
> 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.
First time I see this.
I can reproduce but differently because I miss your perf.data.tar.bz2
that results after the "perf archive" command, then the chains are based
on addresses and not on symbols.
But I found one of these problems on your file even without the symbols:
--- 0x8152b50e
|
|---6.54%-- 0x810e83a7
| 0x810d8590
| 0x810d8710
| 0x81002cbb
| 0xa60ade65
|
|--13.76%-- 0x810dbc9f
| |
| |--44.73%-- 0x810d1ff5
| | |
| | |--38.87%-- 0x810d44c4
| | | 0x810d5242
| | | |
| | | |--82.03%-- 0x810d5f12
| | | | 0x810cbfd7
| | | | 0x810cc046
| | | | 0x810cc1ff
| | | | 0x81002cbb
| | | | 0xa60d37f5
| | | | |
| | | | |--86.66%-- 0xe01170
| | | | |
| | | | --13.34%-- 0x6c632f73
| | | |
| | | --17.97%-- 0x810d629f
| | | 0x810c63a3
| | | 0x810c648b
| | | 0x81002cbb
| | | 0xa60d3cb0
These are not the two last on the chain so it seems to happen even more
randomly.
I'll fix that, thanks!
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