linux-kernel - Re: [LKP] Re: [x86/mce] 1de08dccd3: will-it-scale.per_process

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Date:   Wed, 26 Aug 2020 09:45:58 +0800
From:   Feng Tang <feng.tang@...el.com>
To:     "Luck, Tony" <tony.luck@...el.com>
Cc:     Borislav Petkov <bp@...e.de>,
        "Chen, Rong A" <rong.a.chen@...el.com>,
        LKML <linux-kernel@...r.kernel.org>,
        "lkp@...ts.01.org" <lkp@...ts.01.org>,
        Mel Gorman <mgorman@...e.com>
Subject: Re: [LKP] Re: [x86/mce] 1de08dccd3: will-it-scale.per_process_ops
 -14.1% regression

On Wed, Aug 26, 2020 at 12:44:37AM +0800, Luck, Tony wrote:
> > These 2 variables are accessed in 2 hot call stacks (for this 288 CPU
> > Xeon Phi platform):
> 
> This might be the key element of "weirdness" for this system. It
> has 288 CPUs ... cache alignment problems are often not too bad
> on "small" systems. The as you scale up to bigger machines you
> suddenly hit some critical point and performance drops dramatically.
> 
> It's good that you are picking up tips on how to bisect these and diagnose
> the underlying problem. Number of cores is going to keep increasing, so
> we will keep finding new issues like this.

Yes, now we have one more bullet for shooting this kind of strange
performance changes :)

Thanks,
Feng

> -Tony