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

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Message-ID: <20130411090717.GA14491@gmail.com>
Date:	Thu, 11 Apr 2013 11:07:17 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Waiman Long <Waiman.Long@...com>
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


* Waiman Long <Waiman.Long@...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
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