linux-kernel - Re: Why Semaphore Hardware-Dependent?

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Message-ID: <20060828051409.GA17891@tuatara.stupidest.org>
Date:	Sun, 27 Aug 2006 22:14:09 -0700
From:	Chris Wedgwood <cw@...f.org>
To:	Paul Mackerras <paulus@...ba.org>
Cc:	Dong Feng <middle.fengdong@...il.com>, ak@...e.de,
	Christoph Lameter <clameter@....com>,
	linux-kernel@...r.kernel.org
Subject: Re: Why Semaphore Hardware-Dependent?

On Mon, Aug 28, 2006 at 10:18:35AM +1000, Paul Mackerras wrote:

> I believe the reason for not doing something like this on x86 was
> the fact that we still support i386 processors, which don't have the
> cmpxchg instruction.  That's fair enough, but I would be opposed to
> making semaphores bigger and slower on PowerPC because of that.
> Hence the two different styles of implementation.

The i386 is older than some of the kernel hackers, and given that a
modern kernel is pretty painful with less than say 16MB or RAM in
practice, I don't see that it would be all that terrible to drop
support for ancient CPUs at some point (yes, I know some newer
embedded (and similar) CPUs might be affected here too, but surely not
that many that people really use --- and they could just use 2.4.x).
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