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

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Message-ID: <AANLkTikfxGF_4ZjJXP7kNChkDBnva5iStTPRLs3B86+c@mail.gmail.com>
Date:	Tue, 25 Jan 2011 12:44:45 +1100
From:	Nick Piggin <npiggin@...il.com>
To:	Shaohua Li <shaohua.li@...el.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, Jan 25, 2011 at 12:34 PM, Shaohua Li <shaohua.li@...el.com> wrote:
> 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.

Hm, OK well I could send you a patch to gather some statistics for
why rcu-walk gets dropped. It'll have to wait until I get home, though.
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