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

Roman Zippel
2002-01-12T20:54:13Z

Hi,

Alan Cox wrote:

> So with pre-empt this happens
>
> driver magic
> disable_irq(dev->irq)
> PRE-EMPT:
> [large periods of time running other code]
> PRE-EMPT:
> We get back and we've missed 300 packets, the serial port sharing
> the IRQ has dropped our internet connection completely.

But it shouldn't deadlock as Victor is suggesting.

> There are numerous other examples in the kernel tree where the current code
> knows that there is a small bounded time between two actions in kernel space
> that do not have a sleep. They are not spin locked, and putting spin locks
> 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?

bye, Roman