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Date: Thu, 11 Apr 2013 11:07:17 +0200
From: Ingo Molnar <mingo@kernel.org>
To: Waiman Long <Waiman.Long@hp.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
        Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@redhat.com>,
        "H. Peter Anvin" <hpa@zytor.com>,
        "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
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        Peter Zijlstra <a.p.zijlstra@chello.nl>,
        Andrew Morton <akpm@linux-foundation.org>,
        "Norton, Scott J" <scott.norton@hp.com>,
        Rik van Riel <riel@redhat.com>
Subject: Re: [PATCH RFC 1/3] mutex: Make more scalable by doing less atomic
 operations
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* Waiman Long <Waiman.Long@hp.com> wrote:

> BTW, I have also been thinking about extracting the spinlock out from the mutex 
> structure for some busy mutex by adding a pointer to an external auxiliary 
> structure (separately allocated at init time). The idea is to use the external 
> spinlock if available. Otherwise, the internal one will be used. That should 
> reduce cacheline contention for some of the busiest mutex. The spinner queuing 
> tickets can be in the external structure too. However, it requires a one line 
> change in each of the mutex initialization code. I haven't actually made the 
> code change and try it yet, but that is something that I am thinking of doing 
> when I have time.

I'm not sure per mutex allocations are a really good idea - we like our locking 
primitives to be simple, embeddable into data structures and allocatable together 
with the data structure with no other separate memory footprint.

Thanks,

	Ingo