RE: Direct io on block device has performance regression on 2.6.x kernel

From: Chen, Kenneth W
Date: Wed Mar 09 2005 - 17:57:00 EST

Chen, Kenneth W wrote on Wednesday, March 09, 2005 1:59 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%
> ....
> Profile with spin lock inlined, so that it is easier to see functions
> that has the lock contention, again top 40 hot functions:

Just to clarify here, these data need to be taken at grain of salt. A
high count in _spin_unlock_* functions do not automatically points to
lock contention. It's one of the blind spot syndrome with timer based
profile on ia64. There are some lock contentions in 2.6 kernel that
we are staring at. Please do not misinterpret the number here.

- Ken

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