Subject: Re: [PATCH 1/19] MUTEX: Introduce simple mutex implementation
From: Steven Rostedt <rostedt@goodmis.org>
To: Daniel Walker <dwalker@mvista.com>
Cc: linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org, matthew@wil.cx,
       arjan@infradead.org, hch@infradead.org, akpm@osdl.org,
       torvalds@osdl.org, David Howells <dhowells@redhat.com>,
       Ingo Molnar <mingo@elte.hu>
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References: <dhowells1134431145@warthog.cambridge.redhat.com>
	 <1134435458.22269.11.camel@localhost.localdomain>
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Date: Mon, 12 Dec 2005 22:23:48 -0500
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On Mon, 2005-12-12 at 16:57 -0800, Daniel Walker wrote:
> On Mon, 2005-12-12 at 23:45 +0000, David Howells wrote:
> 
> >  (1) Provides a simple xchg() based semaphore as a default for all
> >      architectures that don't wish to override it and provide their own.
> > 
> >      Overriding is possible by setting CONFIG_ARCH_IMPLEMENTS_MUTEX and
> >      supplying asm/mutex.h
> > 
> >      Partial overriding is possible by #defining mutex_grab(), mutex_release()
> >      and is_mutex_locked() to perform the appropriate optimised functions.
> 
> Your code is really similar to the RT mutex, which does everything that
> your mutex does at least ? Assuming you've reviewed the RT mutex, why
> would we want to use yours over it?

Maybe this would be the better !PREEMPT_RT version.  But the true mutex
that Ingo is making would be used for the PREEMPT_RT side.

This code at least brings down the over head of semaphores where they
are not really needed.  Looking at the code slightly (I must admit, I
spent maybe 30 seconds looking at it), it does seem a little similar to
Ingo's.  Could just be coincidence, since the methods are pretty much
what multiple people would come up with.  But you both work for RedHat,
hmm.

-- Steve


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