linux-kernel - Re: [PATCH RFC 1/3] mutex: Make more scalable by doing less atomic operations

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Message-ID: <51658ADB.4050204@hp.com>
Date:	Wed, 10 Apr 2013 11:52:59 -0400
From:	Waiman Long <Waiman.Long@...com>
To:	Ingo Molnar <mingo@...nel.org>
CC:	Linus Torvalds <torvalds@...ux-foundation.org>,
	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>,
	Davidlohr Bueso <davidlohr.bueso@...com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"Chandramouleeswaran, Aswin" <aswin@...com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Norton, Scott J" <scott.norton@...com>,
	Rik van Riel <riel@...hat.com>
Subject: Re: [PATCH RFC 1/3] mutex: Make more scalable by doing less atomic
 operations

On 04/10/2013 06:31 AM, Ingo Molnar wrote:
> * Waiman Long<Waiman.Long@...com>  wrote:
>
>>> That said, the MUTEX_SHOULD_XCHG_COUNT macro should die. Why shouldn't all
>>> architectures just consider negative counts to be locked? It doesn't matter
>>> that some might only ever see -1.
>> I think so too. However, I don't have the machines to test out other
>> architectures. The MUTEX_SHOULD_XCHG_COUNT is just a safety measure to make sure
>> that my code won't screw up the kernel in other architectures. Once it is
>> confirmed that a negative count other than -1 is fine for all the other
>> architectures, the macro can certainly go.
> I'd suggest to just remove it in an additional patch, Cc:-ing
> linux-arch@...r.kernel.org. The change is very likely to be fine, if not then it's
> easy to revert it.
>
> Thanks,
>
> 	Ingo
Yes, I can do that. So can I put your name down as reviewer or ack'er 
for the 1st patch?

BTW, I am planning to change the code to mimic the 
__mutex_slowpath_needs_to_unlock()  macro so that I only need to update 
the asm/mutex.h only instead of modifying the kernel/mutex.h as well. 
Hope that will make the change more acceptable to others in case we have 
to keep it.

Regards,
Longman
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