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Date:   Tue, 3 Apr 2018 13:23:11 +0200
From:   Peter Zijlstra <peterz@infradead.org>
To:     Thomas Gleixner <tglx@linutronix.de>
Cc:     Li RongQing <lirongqing@baidu.com>,
        LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] genirq: only scan the present CPUs
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On Tue, Apr 03, 2018 at 12:25:56PM +0200, Thomas Gleixner wrote:
> On Mon, 2 Apr 2018, Li RongQing wrote:
> 
> > lots of application will read /proc/stat, like ps and vmstat, but we
> > find the reading time are spreading on Purley platform which has lots
> > of possible CPUs and interrupt.
> > 
> > To reduce the reading time, only scan the present CPUs, not all possible
> > CPUs, which speeds the reading of /proc/stat 20 times on Purley platform
> > which has 56 present CPUs, and 224 possible CPUs
> 
> Why is BIOS/ACPI telling the kernel that there are 224 possible CPUs unless
> it supports physical CPU hotplug.

BIOS is crap, news at 11. I've got boxes like that too. Use
possible_cpu=$nr if you're bothered by it -- it's what I do.