linux-kernel - Re: [lkp] [x86/build] b2c51106c75: -18.1% will-it-scale.per_process

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Message-ID: <CALCETrVhdWVHeLtL72xtOU0qnQM8kVEeAOnxVKKw1tLVeW5Gsg@mail.gmail.com>
Date:	Mon, 10 Aug 2015 13:39:39 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	kernel test robot <ying.huang@...el.com>,
	Andy Lutomirski <luto@...nel.org>, LKP <lkp@...org>,
	LKML <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Thomas Gleixner <tglx@...utronix.de>,
	Denys Vlasenko <dvlasenk@...hat.com>
Subject: Re: [lkp] [x86/build] b2c51106c75: -18.1% will-it-scale.per_process_ops

On Wed, Aug 5, 2015 at 1:38 AM, Ingo Molnar <mingo@...nel.org> wrote:
>
> * kernel test robot <ying.huang@...el.com> wrote:
>
>> FYI, we noticed the below changes on
>>
>> git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git x86/asm
>> commit b2c51106c7581866c37ffc77c5d739f3d4b7cbc9 ("x86/build: Fix detection of GCC -mpreferred-stack-boundary support")
>
> Does the performance regression go away reproducibly if you do:
>
>    git revert b2c51106c7581866c37ffc77c5d739f3d4b7cbc9
>
> ?

FWIW, I spot-checked the generated code.  All I saw were the deletion
of some dummy subtraction from rsp to align the stack for children,
changes of stack frame offsets, and a couple instances in which
instructions got reordered.

--Andy
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