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To: linux-kernel@vger.kernel.org
From: "H. Peter Anvin" <hpa@zytor.com>
Subject: Re: Atomic operations
Date: 3 Jun 2002 11:43:07 -0700
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Followup to:  <EE83E551E08D1D43AD52D50B9F5110927E7A15@ntserver2>
By author:    Gregory Giguashvili <Gregoryg@ParadigmGeo.com>
In newsgroup: linux.dev.kernel
> 
> Could you, please, clarify what you meant saying that there was no way of
> doing so. I admit, I'm no expert in i386 assembly, but this operation seems
> so simple to me...
> 

That doesn't mean the hardware is going to provide it atomically.

> 
> Could you, please, suggest some other implementation (with waiting and
> trying again - whatever this means)?
> 

Very simple:

- Set a spinlock (note: you need a spinlock variable)
- Read
- Add
- Clear spinlock

This is called "bootstrapping" -- using a more primitive atomic
operation to get what you need.

	-hpa
-- 
<hpa@transmeta.com> at work, <hpa@zytor.com> in private!
"Unix gives you enough rope to shoot yourself in the foot."
http://www.zytor.com/~hpa/puzzle.txt	<amsp@zytor.com>
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