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Date: Fri, 21 Jul 2017 15:33:00 +0200
From: Peter Zijlstra <peterz@infradead.org>
To: Joe Perches <joe@perches.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
        Anshul Garg <aksgarg1989@gmail.com>,
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        Will Deacon <will.deacon@arm.com>
Subject: Re: [PATCH] lib/int_sqrt.c: Optimize square root function
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On Fri, Jul 21, 2017 at 03:26:21PM +0200, Peter Zijlstra wrote:
> 
> EVENT=0 -DNEW=1 -DFLS=1
> event: 19.626050 +- 0.038995
> EVENT=0 -DNEW=1 -DFLS=1 -DWIPE_BTB=1
> event: 109.610670 +- 0.425667
> 
> EVENT=0 -DNEW=1 -DFLS=1 -DANSHUL=1
> event: 21.445680 +- 0.043782
> EVENT=0 -DNEW=1 -DFLS=1 -DANSHUL=1 -DWIPE_BTB=1
> event: 83.590420 +- 0.142126
> 

> Let me dig out another GCC version current:
> 
>   gcc (Debian 6.3.0-18) 6.3.0 20170516

gcc-7 (Debian 7.1.0-9) 7.1.0

EVENT=0 -DNEW=1 -DFLS=1
event: 24.179400 +- 0.031344
EVENT=0 -DNEW=1 -DFLS=1 -DWIPE_BTB=1
event: 137.892390 +- 0.307314

EVENT=0 -DNEW=1 -DFLS=1 -DANSHUL=1
event: 22.740300 +- 0.051317
EVENT=0 -DNEW=1 -DFLS=1 -DANSHUL=1 -DWIPE_BTB=1
event: 136.980640 +- 0.223410


GCC regressed it seems... *sigh*