linux-kernel - Re: [PATCH v8 0/9] rwsem performance optimizations

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Date:	Wed, 16 Oct 2013 14:55:30 -0700
From:	Tim Chen <tim.c.chen@...ux.intel.com>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Alex Shi <alex.shi@...aro.org>,
	Andi Kleen <andi@...stfloor.org>,
	Michel Lespinasse <walken@...gle.com>,
	Davidlohr Bueso <davidlohr.bueso@...com>,
	Matthew R Wilcox <matthew.r.wilcox@...el.com>,
	Dave Hansen <dave.hansen@...el.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Rik van Riel <riel@...hat.com>,
	Peter Hurley <peter@...leysoftware.com>,
	"Paul E.McKenney" <paulmck@...ux.vnet.ibm.com>,
	Jason Low <jason.low2@...com>,
	Waiman Long <Waiman.Long@...com>, linux-kernel@...r.kernel.org,
	linux-mm <linux-mm@...ck.org>
Subject: Re: [PATCH v8 0/9] rwsem performance optimizations


> 
> It would be _really_ nice to stick this into tools/perf/bench/ as:
> 
> 	perf bench mem pagefaults
> 
> or so, with a number of parallelism and workload patterns. See 
> tools/perf/bench/numa.c for a couple of workload generators - although 
> those are not page fault intense.
> 
> So that future generations can run all these tests too and such.
> 
> > I compare the throughput where I have the complete rwsem patchset 
> > against vanilla and the case where I take out the optimistic spin patch.  
> > I have increased the run time by 10x from my pervious experiments and do 
> > 10 runs for each case.  The standard deviation is ~1.5% so any changes 
> > under 1.5% is statistically significant.
> > 
> > % change in throughput vs the vanilla kernel.
> > Threads	all	No-optspin
> > 1		+0.4%	-0.1%
> > 2		+2.0%	+0.2%
> > 3		+1.1%	+1.5%
> > 4		-0.5%	-1.4%
> > 5		-0.1%	-0.1%
> > 10		+2.2%	-1.2%
> > 20		+237.3%	-2.3%
> > 40		+548.1%	+0.3%
> 
> The tail is impressive. The early parts are important as well, but it's 
> really hard to tell the significance of the early portion without having 
> an sttdev column.
> 
> ( "perf stat --repeat N" will give you sttdev output, in handy percentage 
>   form. )

Quick naive question as I haven't hacked perf bench before.  
Now perf stat gives the statistics of the performance counter or events.
How do I get it to compute the stats of 
the throughput reported by perf bench?

Something like

perf stat -r 10 -- perf bench mm memset --iterations 10

doesn't quite give what I need.

Pointers appreciated.

Tim

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