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Message-ID: <3C40A255.EBE646@linux-m68k.org>
Date: Sat, 12 Jan 2002 21:53:41 +0100
From: Roman Zippel <zippel@linux-m68k.org>
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To: Alan Cox <alan@lxorguk.ukuu.org.uk>
CC: arjan@fenrus.demon.nl, Rob Landley <landley@trommello.org>,
        linux-kernel@vger.kernel.org
Subject: Re: [2.4.17/18pre] VM and swap - it's really unusable
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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
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