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

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Message-ID: <20140721211801.GA12149@gmail.com>
Date:	Mon, 21 Jul 2014 23:18:01 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Waiman Long <Waiman.Long@...com>
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


* 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
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