linux-kernel - Re: [x86/mce] 7bb39313cd: netperf.Throughput

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Date:   Wed, 20 Jan 2021 13:48:15 +0800
From:   Feng Tang <feng.tang@...el.com>
To:     Borislav Petkov <bp@...en8.de>
Cc:     "Paul E. McKenney" <paulmck@...nel.org>,
        kernel test robot <oliver.sang@...el.com>,
        Jonathan Lemon <bsd@...com>, Tony Luck <tony.luck@...el.com>,
        LKML <linux-kernel@...r.kernel.org>, x86@...nel.org,
        lkp@...ts.01.org, lkp@...el.com, ying.huang@...el.com,
        zhengjun.xing@...el.com
Subject: Re: [x86/mce]  7bb39313cd:  netperf.Throughput_tps -4.5% regression

On Tue, Jan 19, 2021 at 04:33:50PM +0100, Borislav Petkov wrote:
> On Tue, Jan 19, 2021 at 11:09:03PM +0800, Feng Tang wrote:
> > Yes, that can happen. I started a 4 tasks netperf on a 4C/8T KBL desktop,
> > and also saw around 2% improvement. Both the kernel config and the
> > platform matters.
> 
> Oh great. ;-\
> 
> > For the performance changes I have checked, sometimes the change can be
> > reproduced on platforms of different generations (the exact delta number
> > may differs), sometimes it can only be reproduced on one specific platform,
> > like some old generation, or special one like Xeon Phi.
> 
> Probably because that Xeon Phi thing is not as powerful cache-wise as
> some newer ones which have bigger caches and smarter hw prefetchers,
> etc.

Yes, cache size/architecture/policy plays a critical role in these
benchmarking, which is our first thing to check for these strange
kernel performance changes.

Thanks,
Feng