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

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Date:   Wed, 19 Aug 2020 11:15:50 +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>
Subject: Re: [LKP] Re: [x86/mce] 1de08dccd3: will-it-scale.per_process_ops
 -14.1% regression

On Wed, Aug 19, 2020 at 10:23:11AM +0800, Luck, Tony wrote:
> 	0000000000019260 D pqr_state
> 
> Do you have /sys/fs/resctrl mounted?  This variable is read on every context switch.
> If your benchmark does a lot of context switching and this now shares a cache line
> with something different (especially something that is sometimes modified from another
> CPU) that could cause some cache line bouncing.

No, the kernel doesn't has /sys/fs/resctrl mounted.

And the test case is not context switch intensive. It just forks a task
for each CPU which loops running malloc/free and counts the number of
complted operations for 300 seconds.

Thanks,
Feng