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To: Victor Yodaiken <yodaiken@fsmlabs.com>
Cc: BALBIR SINGH <balbir.singh@wipro.com>, linux-kernel@vger.kernel.org
Subject: Re: [RFC] I still see people using cli()
In-Reply-To: <20011008084950.B16204@hq2>
From: ebiederman@uswest.net (Eric W. Biederman)
Date: 08 Oct 2001 09:11:57 -0600
In-Reply-To: <20011008084950.B16204@hq2>
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Victor Yodaiken <yodaiken@fsmlabs.com> writes:

> On Mon, Oct 08, 2001 at 07:59:05PM +0530, BALBIR SINGH wrote:
> > BTW, that brings me to another issue, once the kernel becomes preemptibel,
> what
> 
> > are the locking issues? how are semaphores and spin-locks affected? Has
> anybody
> 
> > defined or come up with the rules/document yet?
> 
> IF the kernel becomes preemptible it will be so slow, so buggy, and so painful
> to maintain, that those issues won't matter.

The preemptible kernel work just takes the current SMP code, and
allows it to work on a single processor.  You are not interruptted if
you have a lock held.  This makes the number of cases in the kernel
simpler, and should improve maintenance as more people will be
affected by the SMP issues.

Right now there is a preemptible kernel patch being maintained
somewhere.  I haven't had a chance to look recently.  But the recent
threads on low latency mentioned it.

As for rules.  They are the usual SMP rules.  In earlier version there
was a requirement or that you used balanced constructs.

i.e.
spin_lock_irqsave
...
spin_unlock_irqrestore

and not.

spin_lock_irqsave
...
spin_unlock
..
restore_flags.


Eric
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