linux-kernel - Re: more dput lock contentions in 2.6.38-rc?

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Date:	Tue, 25 Jan 2011 09:34:18 +0800
From:	Shaohua Li <shaohua.li@...el.com>
To:	Nick Piggin <npiggin@...il.com>
Cc:	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
	lkml <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Nick Piggin <npiggin@...nel.dk>,
	"Chen, Tim C" <tim.c.chen@...el.com>
Subject: Re: more dput lock contentions in 2.6.38-rc?

On Tue, 2011-01-25 at 09:26 +0800, Nick Piggin wrote:
> On Tue, Jan 25, 2011 at 12:11 PM, Shaohua Li <shaohua.li@...el.com> wrote:
> > On Tue, 2011-01-25 at 09:04 +0800, Nick Piggin wrote:
> >> On Tue, Jan 25, 2011 at 11:35 AM, Shaohua Li <shaohua.li@...el.com> wrote:
> >> > Hi,
> >> > we are testing dbench benchmark and see big drop of 2.6.38-rc compared
> >> > to 2.6.37 in several machines with 2 sockets or 4 sockets. We have 12
> >> > disks mount to /mnt/stp/dbenchdata/sd*/ and dbench runs against data of
> >> > the disks. According to perf, we saw more lock contentions:
> >> > In 2.6.37: 13.00%        dbench  [kernel.kallsyms]   [k] _raw_spin_lock
> >> > In 2.6.38-rc: 69.45%        dbench  [kernel.kallsyms]   [k]_raw_spin_lock
> >> > -     69.45%        dbench  [kernel.kallsyms]   [k] _raw_spin_lock
> >> >   - _raw_spin_lock
> >> >      - 48.41% dput
> >> >         - 61.17% path_put
> >> >            - 60.47% do_path_lookup
> >> >               + 53.18% user_path_at
> >> >               + 42.13% do_filp_open
> >> >               + 4.69% user_path_parent
> >>
> >> What filesystems are mounted on the path?
> > ext3 or ext4
> 
> ext3 or 4 along every step of the path? Are there
> any acls loaded, or security policy running?
all disks are formated with the same fs, just some machines use ext3 and
others ext4. no we don't have acl or security policy.
> It may be possible that they're all coming from
> /proc/ access.
I added trace in dput just after the lock taken. and most files are '/',
'mnt', 'stp'. the percentage of 'proc' is small actually.

Thanks,
Shaohua

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