linux-kernel - Re: [LKP] [sched/numa] a43455a1d57: +94.1% proc-vmstat.numa_hint_faults

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Message-ID: <20140801081423.GA21249@localhost>
Date:	Fri, 1 Aug 2014 16:14:23 +0800
From:	Fengguang Wu <fengguang.wu@...el.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Aaron Lu <aaron.lu@...el.com>, Rik van Riel <riel@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>, lkp@...org,
	jhladky@...hat.com
Subject: Re: [LKP] [sched/numa] a43455a1d57: +94.1%
 proc-vmstat.numa_hint_faults_local

On Fri, Aug 01, 2014 at 09:29:11AM +0200, Peter Zijlstra wrote:
> On Fri, Aug 01, 2014 at 10:03:30AM +0800, Aaron Lu wrote:
> > > > > ebe06187bf2aec1  a43455a1d572daf7b730fe12e  
> > > > > ---------------  -------------------------  
> > > > >      94500 ~ 3%    +115.6%     203711 ~ 6%  ivb42/hackbench/50%-threads-pipe
> > > > >      67745 ~ 4%     +64.1%     111174 ~ 5%  lkp-snb01/hackbench/50%-threads-socket
> > > > >     162245 ~ 3%     +94.1%     314885 ~ 6%  TOTAL proc-vmstat.numa_hint_faults_local
> 
> > It means, for commit ebe06187bf2aec1, the number for
> > num_hint_local_faults is 94500 for ivb42 machine and 67745 for lkp-snb01
> > machine. The 3%, 4% following that number means the deviation of the
> > different runs to their average(we usually run it multiple times to
> > phase out possible sharp values). We should probably remove that
> > percentage, as they cause confusion if no detailed explanation and may
> > not mean much to the commit author and others(if the deviation is big
> > enough, we should simply drop that result).
> 
> Nah, variance is good, but the typical symbol would be +- or the fancy
> ±.
> 
> ~ when used as a unary op means 'approx' or 'about' or 'same order'
> ~ when used as a binary op means equivalence, a weaker equal, often in
> the vein of the unary op meaning.
> 
> Also see: http://en.wikipedia.org/wiki/Tilde#Mathematics
> 
> So while I think having a measure of variance is good, I think you
> picked entirely the wrong symbol.

Good point! We'll first try ± for the stddev percent and fall back to
+- if it turn out to not work well in some cases.

Thanks,
Fengguang
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