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SubjectRe: -rt dbench scalabiltiy issue
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On Mon, 2009-11-23 at 10:06 +0100, Nick Piggin wrote:
> BTW. Have you tested like ext4, xfs and btrfs cases? I don't think ext3
> is likely to see a huge amount of scalability work, and so it will be
> good to give an early heads up to the more active projects...

Yea, I need to give those a shot. I also generated the same numbers as
before with ext2 (all the raw numbers are in dbench-scalability dir):

http://sr71.net/~jstultz/dbench-scalability/graphs/ext2-scalability.png

Again, its similar to ext3, in that all the -rt variants are hitting
some contention issues. But I was a little surprised to see
2.6.32-rc7-nick below 2.6.32-rc7 there, so generated perf data there as
well:

http://sr71.net/~jstultz/dbench-scalability/perflogs/2.6.32-rc7-nick.ext2.perflog


31.91% dbench [kernel] [k] _spin_lock
|
|--44.17%-- dput
| |
| |--50.39%-- __link_path_walk
| | |
| | |--99.88%-- path_walk
| | | |
| | | |--96.18%-- do_path_lookup
| | | | |
| | | | |--51.49%-- user_path_at
| | | | | |
| | | | | |--96.84%-- vfs_fstatat
| | | | | | vfs_stat
| | | | | | sys_newstat
| | | | | | system_call_fastpath
| | | | | | _xstat
| | | | | |
| | | | | --3.16%-- do_utimes
| | | | | sys_utime
| | | | | system_call_fastpath
| | | | | __GI_utime
| | | | |
| | | | |--43.18%-- do_filp_open
| | | | | do_sys_open
| | | | | sys_open
| | | | | system_call_fastpath
| | | | | __GI___open
...

|--39.98%-- path_get
| |
| |--51.19%-- path_init
| | |
| | |--96.40%-- do_path_lookup
| | | |
| | | |--55.12%-- user_path_at
| | | | |
| | | | |--91.47%-- vfs_fstatat
| | | | | vfs_stat
| | | | | sys_newstat
| | | | | system_call_fastpath
| | | | | _xstat
| | | | | |
| | | | | --100.00%-- 0x7478742e746e65
| | | | |


So I'm a little confused here. Why is dput/path_get showing up in ext2
when it all but disappeared with ramfs? Does ramfs have some sort of
vfs_stat shortcut that avoids whatever is catching us here?

thanks
-john



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