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    SubjectRe: more dput lock contentions in 2.6.38-rc?
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    On Tue, Jan 25, 2011 at 12:34 PM, Shaohua Li <shaohua.li@intel.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@intel.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@intel.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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