linux-kernel - Re: [Question or BUG] [NUMA]: I feel puzzled at the function cpumask_of

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Message-ID: <20170608141214.GJ19866@dhcp22.suse.cz>
Date:   Thu, 8 Jun 2017 16:12:15 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     "Leizhen (ThunderTown)" <thunder.leizhen@...wei.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        linux-mm <linux-mm@...ck.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        chenchunxiao <chenchunxiao@...wei.com>, x86l <x86@...nel.org>,
        linux-api@...r.kernel.org
Subject: Re: [Question or BUG] [NUMA]: I feel puzzled at the function
 cpumask_of_node

[CC linux-api]

On Wed 07-06-17 17:23:20, Leizhen (ThunderTown) wrote:
> When I executed numactl -H(print cpumask_of_node for each node), I got
> different result on X86 and ARM64.  For each numa node, the former
> only displayed online CPUs, and the latter displayed all possible
> CPUs.  Actually, all other ARCHs is the same to ARM64.
> 
> So, my question is: Which case(online or possible) should function
> cpumask_of_node be? Or there is no matter about it?

Unfortunatelly the documentation is quite unclear
What:		/sys/devices/system/node/nodeX/cpumap
Date:		October 2002
Contact:	Linux Memory Management list <linux-mm@...ck.org>
Description:
		The node's cpumap.

not really helpeful, is it? Semantically I _think_ printing online cpus
makes more sense because it doesn't really make much sense to bind
anything on offline nodes. Generic implementtion of cpumask_of_node
indeed provides only online cpus. I haven't checked specific
implementations of arch specific code but listing offline cpus sounds
confusing to me.

-- 
Michal Hocko
SUSE Labs