linux-kernel - Re: MIPS atomic operations, "sync"

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Message-ID: <20061110223303.GA17712@linux-mips.org>
Date:	Fri, 10 Nov 2006 22:33:04 +0000
From:	Ralf Baechle <ralf@...ux-mips.org>
To:	Mathieu Desnoyers <compudj@...stal.dyndns.org>
Cc:	linux-kernel@...r.kernel.org, ltt-dev@...fik.org
Subject: Re: MIPS atomic operations, "sync"

On Fri, Nov 10, 2006 at 01:40:49PM -0500, Mathieu Desnoyers wrote:

> I am currently creating a "LOCK" prefix free and memory barrier free version
> of atomic.h to fulfill my tracer (LTTng) needs, which is to atomically update
> per-cpu data and have a minimal performance loss.
> 
> I just came across the MIPS atomic.h and system.h implementations in 2.6.18
> which brings a question :
> 
> Why are the primitives in include/asm-mips/atomic.h using the "sync"
> instruction even in the UP case ? system.h cmpxchg only uses the sync in the
> SMP case.

Why are the standard atomic operations insufficient for your needs?

There is an enormous amout of subtilities in those atomic ops for some
architectures you probably do yourself a big favor by avoiding new
variants.

  Ralf
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