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Subject: Re: Preempt & how long it takes to interrupt (was Re:
	[2.4.17/18pre] VM and swap - it's really unusable)
From: Robert Love <rml@tech9.net>
To: Pavel Machek <pavel@suse.cz>
Cc: Helge Hafting <helgehaf@aitel.hist.no>,
        Rob Landley <landley@trommello.org>, linux-kernel@vger.kernel.org
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On Fri, 2002-01-18 at 17:41, Pavel Machek wrote:

> So... how long do you have to stay in interrupt for it to be a bug?
> 
> There's *no* requirement that says "it may not take second to handle
> an interrupt". Actually I guess that some nasty conditions (UHCI needs
> reset?) may take that long in interrupt. Oh and actually few releases
> ago, console switching was done from interrupt and it *did* take 2
> seconds for me.
> 
> If someone assumes interrupts are "short", he has broken code already.

Agreed.  Conversely, however, writing code that introduces long
interrupt-off periods should be considered a BUG.

In other words, relying on short interrupt-off periods is bad form, but
so is writing gross code that rudely keeps them off.

I think we all considered the long off periods in VT switching and fbdev
a bug.

	Robert Love

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