Re: buggy perf callgraph output
From: Nick Piggin
Date: Fri Dec 17 2010 - 00:33:21 EST
On Thu, Dec 16, 2010 at 12:47:58PM +0100, Frederic Weisbecker wrote:
> 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.
Oh I didn't realize perf archive, noted for next time, thanks.
> 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!
That would be great, thanks! It's a really awesome tool, I appreciate
your effort on it.
Thanks,
Nick
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