linux-kernel - Re: [PATCH 1/2] x86/cpu hotplug: make apicid <--> cpuid mapping persistent

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Date:	Thu, 26 Mar 2015 11:13:12 -0400
From:	Tejun Heo <tj@...nel.org>
To:	Gu Zheng <guz.fnst@...fujitsu.com>
Cc:	Kamezawa Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	linux-kernel@...r.kernel.org, laijs@...fujitsu.com,
	isimatu.yasuaki@...fujitsu.com, tangchen@...fujitsu.com,
	izumi.taku@...fujitsu.com
Subject: Re: [PATCH 1/2] x86/cpu hotplug: make apicid <--> cpuid mapping
 persistent

On Thu, Mar 26, 2015 at 12:55:04PM +0800, Gu Zheng wrote:
> >> +static int apicid_to_x86_cpu[MAX_LOCAL_APIC] = {
> >> +	[0 ... MAX_LOCAL_APIC - 1] = -1,
> >> +};
> > 
> > 
> > This patch cannot handle x2apic, which is 32bit.
> 
> IMO, if the apicid is too big (larger than MAX_LOCAL_APIC), we will skip
> generating a logic cpu number for it, so it seems no problem here.

You're defining 128k array on 64bit most of which will be unused on
most machines.  There is a problem with that.

Thanks.

-- 
tejun
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