linux-kernel - Re: [LKP] [lkp] [x86/platform/UV] 71854cb812: will-it-scale.per_thread

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Date:   Mon, 31 Oct 2016 12:19:16 -0600 (MDT)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Fengguang Wu <fengguang.wu@...el.com>
cc:     Ye Xiaolong <xiaolong.ye@...el.com>, Russ Anderson <rja@....com>,
        Dimitri Sivanich <sivanich@....com>,
        Matt Fleming <matt@...eblueprint.co.uk>, x86@...nel.org,
        LKML <linux-kernel@...r.kernel.org>,
        Mike Travis <travis@....com>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Alex Thorlton <athorlton@....com>, lkp@...org
Subject: Re: [LKP] [lkp] [x86/platform/UV] 71854cb812: will-it-scale.per_thread_ops
 -2.3% regression

On Mon, 31 Oct 2016, Fengguang Wu wrote:
> On Fri, Oct 28, 2016 at 12:37:45AM +0200, Thomas Gleixner wrote:
> > I have no explanation for this either, but you really should try to figure
> > out what's going on here.
> 
> Xiaolong, how about doing a small debug patch (a WARN_ONCE() line may
> be enough) to verify whether the code path is executed?
> 
> It'd also help to compare vmlinux according to Thomas' reasoning:
> 
> > The only difference between plain rc1 and rc + this patch is the resulting
> > text size and therefor some other unrelated stuff moving to different
> > places in memory which has some yet to figure out side effects.

So one other thing you might try is using rc3 as a base line and then
revert the patch in question on top of rc3 and see whether that weird
behaviour persists.
 
> > From bisect POV, the below graphs show the user_time and system_time
> are clearly and consistently different before/after commit 71854cb812.
> So this commit must impacted something.

I agree. I just have no idea what happens.

Thanks,

	tglx