Re: udelay() & preemption & drifty ITCs

From: Jesse Barnes <jbarnes_at_sgi.com>
Date: 2003-11-24 09:39:29
On Sat, Nov 22, 2003 at 09:45:25PM -0600, Jack Steiner wrote:
> I may be overlooking something, but isnt there a problem
> with the udelay() function on IA64 platforms with drifty ITCs
> when preemption is enabled.
> 
> The function uses the ITC for timing. If preemption occurs & the process
> migrates to a different cpu with a much larger ITC value, it
> seems like the delay may be satisfied too quickly.

Yep, it appears so.  I guess we need a 'preempt_disable/disable()' pair
around the itc access.  Of course, callers under a spinlock are already
protected, so maybe exposure to this problem isn't that large?

Jesse
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Received on Sun Nov 23 17:41:30 2003

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