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Re: Observations on LLSC and SMP

To: Ed Martini <martini@c2micro.com>
Subject: Re: Observations on LLSC and SMP
From: Daniel Jacobowitz <dan@debian.org>
Date: Fri, 25 Mar 2005 14:37:59 -0500
Cc: linux-mips@linux-mips.org
In-reply-to: <42446555.6090005@c2micro.com>
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References: <4230DB4C.7090103@c2micro.com> <20050314110101.GF7759@linux-mips.org> <423763B9.2000907@c2micro.com> <20050316120647.GB8563@linux-mips.org> <42446555.6090005@c2micro.com>
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On Fri, Mar 25, 2005 at 11:24:05AM -0800, Ed Martini wrote:
> 1. If the first part of the if were an ifdef instead it would result in 
> a code size reduction as well as a runtime performance gain.

You should spend a little time playing with an optimizing compiler. 
They're capable of working out when a condition will always be false.

> 2. In atomic.h the "C lang stuff" is wrapped with a spinlock.  In the 
> SMP case the spinlock will result in code that contains ll and sc 
> instructions, so I infer that there are no SMP system configs that use 
> CPUs that don't have the ll and sc instructions. 

That's correct.  It is not practical to implement SMP without a mutex
primitive.


-- 
Daniel Jacobowitz
CodeSourcery, LLC

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