linux-kernel - Re: [RFC PATCH 0/5] futex: introduce an optimistic spinning futex

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Message-ID: <53CEBD2F.2040705@hp.com>
Date:	Tue, 22 Jul 2014 15:36:15 -0400
From:	Waiman Long <waiman.long@...com>
To:	Ingo Molnar <mingo@...nel.org>
CC:	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>,
	Darren Hart <dvhart@...ux.intel.com>,
	Davidlohr Bueso <davidlohr@...com>,
	Heiko Carstens <heiko.carstens@...ibm.com>,
	linux-kernel@...r.kernel.org, linux-api@...r.kernel.org,
	linux-doc@...r.kernel.org, Jason Low <jason.low2@...com>,
	Scott J Norton <scott.norton@...com>
Subject: Re: [RFC PATCH 0/5] futex: introduce an optimistic spinning futex

On 07/21/2014 05:18 PM, Ingo Molnar wrote:
> * Waiman Long<Waiman.Long@...com>  wrote:
>
>> Testing done on a 4-socket Westmere-EX boxes with 40 cores (HT off)
>> showed the following performance data (average kops/s) with various
>> load factor (number of pause instructions) used in the critical
>> section using an userspace mutex microbenchmark.
>>
>>    Threads  Load	Waiting Futex	Spinning Futex 	  %Change
>>    -------  ----	-------------	--------------	  -------
>>      256	     1	     6894	    8883	    +29%
>>      256	    10	     3656	    4912	    +34%
>>      256	    50	     1332	    4358	   +227%
>>      256	   100	      792	    2753	   +248%
>>       10	     1	     6382	    4838	    -24%
>>       10	    10	     3614	    4748	    +31%
>>       10	    50	     1319	    3900	   +196%
>>       10	   100	      782	    2459	   +214%
>>        2	     1	     7905	    7194	   -9.0%
>>        2	    10	     4556	    4717	   +3.5%
>>        2	    50	     2191	    4167	    +90%
>>        2	   100	     1767	    2407	    +36%
> So the numbers look interesting - but it would be _really_ important
> to provide noise/sttdev figures in a sixth column as well (denoted in
> percentage units, not in benchmark units), so that we know how
> significant a particular speedup (or slowdown) is.
>
> Thanks,
>
> 	Ingo

The performance can varies quite a bit depending on what other processes 
are running at the test execution time. I will include stddev data in 
the next iteration of the patch.

-Longman
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