Re: Strange performance change 59 -> 61/62

["Martin J. Bligh" <mbligh@aracnet.com>]

>>> I'm comparing 59-mjb6 to 61-mjb1 and notice some strange performance
>>> differences that I can't explain ... not a big drop, but odd.
>>> ...
>>> 
>>> 1562 .text.lock.file_table
>>> 583 dentry_open
>>> 551 get_empty_filp
>> 
>> The first one here is fget().  That's causing problems on ppc64 as well - the
>> machine is spending as long in fget as it is in copy_foo_user() in dbench
>> runs.
>> 
>> One possibility is that we're calling fget() more often than previously,
>> although that would be rather odd.  Can you add the below patch, and monitor
>> /proc/meminfo:nr_fgets?

Some more stats ... which look rather suspicious. 600% increase for
dentry_open and __mark_inode_dirty? Hmmmmm.

      5198    35.9% .text.lock.file_table
      4562     2.6% total
       736    19.5% get_empty_filp
       568   617.4% dentry_open
       510   607.1% __mark_inode_dirty
       285    11.3% atomic_dec_and_lock
       272    11.9% __fput
       230    23.0% dput
       167     8.9% file_move
       159     1.0% page_remove_rmap
       128    67.7% vma_merge
       118    17.1% current_kernel_time
        66     1.0% page_add_rmap
        62     0.0% can_vma_merge_after
        50     2.3% do_schedule
...
       -56   -16.0% do_brk
       -67    -8.5% sys_brk
       -73    -0.5% do_anonymous_page
       -83   -45.6% do_lookup
      -109   -11.3% fd_install
      -114    -3.9% __copy_from_user_ll
      -133   -10.9% do_generic_mapping_read
      -282   -18.4% vfs_read
      -314   -34.4% file_ra_state_init
      -373    -7.7% vm_enough_memory
      -445    -5.5% d_lookup
     -1693    -3.8% default_idle