ext3_group_sparse slow?

[Jan Kara <jack@suse.cz>]

  Hello!

  I've been profiling dbench load on ext3 on my laptop and it looks as
follows:
CPU: CPU with timer interrupt, speed 0 MHz (estimated)
Profiling through timer interrupt
samples  %        symbol name
100485   23.2633  __copy_to_user_ll
54497    12.6166  __copy_from_user_ll
34702     8.0339  acpi_processor_idle
15107     3.4974  link_path_walk
8229      1.9051  __d_lookup
6540      1.5141  ext3_group_sparse
6490      1.5025  __might_sleep
4972      1.1511  sysenter_past_esp
3981      0.9216  kmem_cache_alloc
3797      0.8790  ext3_readdir
3617      0.8374  find_get_page
3615      0.8369  ext3_get_group_desc
3589      0.8309  ext3_do_update_inode
...

  What caught my eye is that ext3_group_sparse() and also
ext3_get_group_desc() take so much time. OK, it's only 1.51 and 0.84 percent
of the processor time and it is clearly pretty much dominated by the IO
but anyway I think we need not spend so much processor time by such
trivial operations :) Do you think it would be worth improving?

								Honza

-- 
Jan Kara <jack@suse.cz>
SuSE CR Labs