Re: [2.4.17/18pre] VM and swap - it's really unusable

[Alan Cox <alan _at_ lxorguk.ukuu.org.uk>]

> > everywhere will just trash performance. They are pure hardware interactions
> > so you can't automatically detect them.
> 
> Why should spin locks trash perfomance, while an expensive disable_irq()
> doesn't?

disable_irq only blocks _one_ interrupt line, spin_lock_irqsave locks the
interrupt off on a uniprocessor, and  50% of the time off on a
dual processor. 

If I use a spin lock you can't run a modem and an NE2000 card together on
Linux 2.4. Thats why I had to do that work on the code. Its one of myriads
of basic obvious cases that the pre-empt patch gets wrong

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