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SubjectRE: Direct io on block device has performance regression on 2.6.x kernel
Date
Andrew Morton wrote on Wednesday, March 09, 2005 2:45 PM
> >
> > > Did you generate a kernel profile?
> >
> > Top 40 kernel hot functions, percentage is normalized to kernel utilization.
> >
> > _spin_unlock_irqrestore 23.54%
> > _spin_unlock_irq 19.27%
>
> Cripes.
>
> Is that with CONFIG_PREEMPT? If so, and if you disable CONFIG_PREEMPT,
> this cost should be accounting the the spin_unlock() caller and we can see
> who the culprit is. Perhaps dio->bio_lock.

CONFIG_PREEMPT is off.

Sorry for all the confusion, I probably shouldn't post the first profile
to confuse people. See 2nd profile that I posted earlier (copied here again).

scsi_request_fn 7.54%
finish_task_switch 6.25%
__blockdev_direct_IO 4.97%
__make_request 3.87%
scsi_end_request 3.54%
dio_bio_end_io 2.70%
follow_hugetlb_page 2.39%
__wake_up 2.37%
aio_complete 1.82%
kmem_cache_alloc 1.68%
__mod_timer 1.63%
e1000_clean 1.57%
__generic_file_aio_read 1.42%
mempool_alloc 1.37%
put_page 1.35%
e1000_intr 1.31%
schedule 1.25%
dio_bio_complete 1.20%
scsi_device_unbusy 1.07%
kmem_cache_free 1.06%
__copy_user 1.04%
scsi_dispatch_cmd 1.04%
__end_that_request_first1.04%
generic_make_request 1.02%
kfree 0.94%
__aio_get_req 0.93%
sys_pread64 0.83%
get_request 0.79%
put_io_context 0.76%
dnotify_parent 0.73%
vfs_read 0.73%
update_atime 0.73%
finished_one_bio 0.63%
generic_file_aio_write_nolock 0.63%
scsi_put_command 0.62%
break_fault 0.62%
e1000_xmit_frame 0.62%
aio_read_evt 0.59%
scsi_io_completion 0.59%
inode_times_differ 0.58%


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