Re: more dput lock contentions in 2.6.38-rc?
From: Nick Piggin
Date: Mon Jan 24 2011 - 20:26:44 EST
On Tue, Jan 25, 2011 at 12:11 PM, Shaohua Li <shaohua.li@xxxxxxxxx> 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@xxxxxxxxx> 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?
It may be possible that they're all coming from
>> > - 35.56% d_path
>> > seq_path
>> > show_vfsmnt
>> > seq_read
>> > vfs_read
>> > sys_read
>> > system_call_fastpath
>> > __GI___libc_read
>> This guy is from glibc's statvfs call that dbench uses. It
>> parses /proc/mounts for mount flags which is racy (and
>> not a good idea to do with any frequency).
>> A patch went into the kernel that allows glibc to get the
>> flags directly. Not sure about glibc status, I imagine it
>> will get there in another decade or two... Can you try
>> commenting it out of dbench source code?
> Sure, maybe after Chinese new year holiday, sorry.
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