linux-kernel - Re: [PATCH 0/3 v2] mutex: Improve mutex performance by doing less atomic-ops & better spinning

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Date:	Tue, 16 Apr 2013 07:49:50 -0400
From:	Waiman Long <Waiman.Long@...com>
To:	Ingo Molnar <mingo@...nel.org>
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, x86@...nel.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 0/3 v2] mutex: Improve mutex performance by doing less
 atomic-ops & better spinning

On 04/16/2013 05:12 AM, Ingo Molnar wrote:
> * Waiman Long<Waiman.Long@...com>  wrote:
>
>> [...]
>>
>> Patches 2 improves the mutex spinning process by reducing contention among the
>> spinners when competing for the mutex. This is done by using a MCS lock to put
>> the spinners in a queue so that only the first spinner will try to acquire the
>> mutex when it is available. This patch showed significant performance
>> improvement of +30% on the AIM7 fserver and new_fserver workload.
> Ok, that's really nice - and this approach has no arbitrary limits/tunings in it.
>
> Do you have a performance comparison to your first series (patches 1+2+3 IIRC) -
> how does this new series with MCS locking compare to the best previous result from
> that old series? Do we now achieve that level of performance?

Compared with the old patch set, the new patches 1+2 have over 30% 
performance gain in high user load (1100-1500) in the fserver and 
new_fserver workloads. The old patches 1+2 or 1+3 only manages around 
10% gain. In the intermediate range of 200-1000, the 2 sets are more 
comparable in performance gain.

Regards,
Longman
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