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From: Roger Larsson <roger.larsson@norran.net>
To: Pavel Machek <pavel@ucw.cz>, alan@lxorguk.ukuu.org.uk
Subject: Re: preempt & ne2k
Date: Mon, 28 Jan 2002 21:18:02 +0100
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On Sunday den 27 January 2002 21.52, Pavel Machek wrote:
> Hi!
>
> > > testing the patch complaining about, AND one that seems like it could
> > > be addressed by using IRQ disabling as a latency guard in addition to
> > > spinlocks.
> >
> > I dont believe anyone has tested the driver hard with pre-empt. Its not
> > that this driver can't be fixed. Its that this is one tiny example of
> > maybe thousands of other similar flaws lurking. There is no obvious
> > automated way to find them either.
>
> So.... you have shown performance problem in one driver. Maybe *bad*
> performance problem, but only performance problem. There may be other
> performance problems out there. And what?
> 								Pavel

In Alans example it is not a performance problem - it is more of a 
correctness problem.

The case when a driver were disabling a specific interrupt was not handled
in a 100% correct way.

There are some other cases that might be even harder to detect - disabling
from a device by writing in its control register.

But if the preempt patch is added those critical sections can be protected.

It is not trivial nor impossible...

/RogerL

-- 
Roger Larsson
Skellefte?
Sweden
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