linux-kernel - Re: [PATCH v2 optional 3/3] mutex: back out architecture specific check for negative mutex count

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Message-ID: <516D3FCD.9060703@hp.com>
Date:	Tue, 16 Apr 2013 08:10:53 -0400
From:	Waiman Long <Waiman.Long@...com>
To:	Will Deacon <will.deacon@....com>
CC:	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	David Howells <dhowells@...hat.com>,
	Dave Jones <davej@...hat.com>,
	Clark Williams <williams@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"x86@...nel.org" <x86@...nel.org>,
	"linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
	"Chandramouleeswaran, Aswin" <aswin@...com>,
	Davidlohr Bueso <davidlohr.bueso@...com>,
	"Norton, Scott J" <scott.norton@...com>,
	Rik van Riel <riel@...hat.com>
Subject: Re: [PATCH v2 optional 3/3] mutex: back out architecture specific
 check for negative mutex count

On 04/16/2013 06:05 AM, Will Deacon wrote:
> On Mon, Apr 15, 2013 at 03:37:59PM +0100, Waiman Long wrote:
>> If it is confirmed that all the supported architectures can allow a
>> negative mutex count without incorrect behavior, we can then back
>> out the architecture specific change and allow the mutex count to
>> go to any negative number. That should further reduce contention for
>> non-x86 architecture.
>>
>> If this is not the case, this patch should be dropped.
> A good starting point might be to look at the asm-generic mutex
> implementations, which clears up the majority of architectures. A cursory
> glance at mutex-dec.h suggests that it's OK to me...

I think the generic version is fine with negative mutex count. However, 
it is the architecture specific versions (we have 22 of them as of 3.8) 
that I am worry about. I just don't have enough know-how and test 
machines to verify that.

Regards,
Longman
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