linux-kernel - Re: [lkp-robot] [x86/mm] c4c3c3c2d0: will-it-scale.per_process

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Date:   Mon, 16 Oct 2017 12:15:48 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     kernel test robot <xiaolong.ye@...el.com>,
        Andy Lutomirski <luto@...nel.org>
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org,
        Markus Trippelsdorf <markus@...ppelsdorf.de>,
        Adam Borowski <kilobyte@...band.pl>,
        Brian Gerst <brgerst@...il.com>,
        Johannes Hirte <johannes.hirte@...enkhaos.de>, lkp@...org
Subject: Re: [lkp-robot] [x86/mm]  c4c3c3c2d0:  will-it-scale.per_process_ops
 -61.0% regression

On Mon, Oct 16, 2017 at 10:39:17AM +0800, kernel test robot wrote:
> 
> Greeting,
> 
> FYI, we noticed a -61.0% regression of will-it-scale.per_process_ops due to commit:
> 
> 
> commit: c4c3c3c2d00826c88b5c02c20e80704664424b9b ("x86/mm: Flush more aggressively in lazy TLB mode")
> url: https://github.com/0day-ci/linux/commits/Borislav-Petkov/x86-mm-Flush-more-aggressively-in-lazy-TLB-mode/20171011-115901
> 
> 
> in testcase: will-it-scale
> on test machine: 88 threads Intel(R) Xeon(R) CPU E5-2699 v4 @ 2.20GHz with 64G memory

Say what now?

This is actually what got applied upstream:

b956575bed91 ("x86/mm: Flush more aggressively in lazy TLB mode")

and AFAICT, that machine is BDW and it should have PCID, right?

Or wait, that's a guest so PCID is probably not even usable for guests.
Or should we disable it in VMs?

I'm confused. Andy?

-- 
Regards/Gruss,
    Boris.

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