linux-kernel - Re: nr_cpu_ids incorrect on AMD Quad-Core Opteron 8380

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Message-ID: <20100203072123.GA5428@liondog.tnic>
Date:	Wed, 3 Feb 2010 08:21:23 +0100
From:	Borislav Petkov <petkovbb@...glemail.com>
To:	zhiyi <zhuang@...otago.ac.nz>
Cc:	linux-kernel@...r.kernel.org, jkmair@...otago.ac.nz
Subject: Re: nr_cpu_ids incorrect on AMD Quad-Core Opteron 8380

On Wed, Feb 03, 2010 at 10:33:46AM +1300, zhiyi wrote:
> The good thing is that I realized I should use num_present_cpus()
> instead of nr_cpu_ids for my purpose (get the number of real cores
> on the machine)

Just a minor thing: there could be a subtlety with hotplug when
using num_present_cpus() since this includes all CPUs, even the
hotplug-offlined ones. Depending on your case, you might want to use
num_online_cpus() instead. Look at the comment at the beginning of
<include/linux/cpumask.h> which explains all the different masks to
figure out which one fits your needs best.

-- 
Regards/Gruss,
    Boris.
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