linux-kernel - Re: [lkp] [x86/hweight] 65ea11ec6a: will-it-scale.per_process

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Message-ID: <796A2A72-06B7-4B3D-AA38-DF558FC75857@zytor.com>
Date:	Tue, 16 Aug 2016 16:09:19 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Borislav Petkov <bp@...e.de>
CC:	kernel test robot <xiaolong.ye@...el.com>,
	Ville Syrjälä <ville.syrjala@...ux.intel.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andy Lutomirski <luto@...capital.net>,
	Brian Gerst <brgerst@...il.com>,
	Denys Vlasenko <dvlasenk@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>, lkp@...org
Subject: Re: [lkp] [x86/hweight]  65ea11ec6a:  will-it-scale.per_process_ops 9.3% improvement

On August 16, 2016 10:16:35 AM PDT, Borislav Petkov <bp@...e.de> wrote:
>On Tue, Aug 16, 2016 at 09:59:00AM -0700, H. Peter Anvin wrote:
>> Dang...
>
>Isn't 9.3% improvement a good thing(tm) ?

Yes, it's huge.  The only explanation I could imagine is that scrambling %rdi caused the scheduler to do completely the wrong thing.
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