linux-kernel - Re: [PATCH] Avoid mask based num_possible_cpus and num_online

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Date:	Mon, 13 Feb 2012 13:57:45 -0800
From:	Tony Luck <tony.luck@...il.com>
To:	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>
Cc:	Rusty Russell <rusty@...tcorp.com.au>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Venkatesh Pallipadi <venki@...gle.com>,
	KOSAKI Motohiro <kosaki.motohiro@...il.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Mike Travis <travis@....com>,
	"Paul E. McKenney" <paul.mckenney@...aro.org>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Paul Gortmaker <paul.gortmaker@...driver.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Avoid mask based num_possible_cpus and num_online_cpus -v5

On Mon, Feb 13, 2012 at 12:44 PM, Srivatsa S. Bhat
<srivatsa.bhat@...ux.vnet.ibm.com> wrote:
> IOW, what output do you see from the following printk from
> arch/ia64/kernel/smpboot.c?
>
> printk(KERN_INFO "Total of %d processors activated (%lu.%02lu BogoMIPS).\n",
>         (int)num_online_cpus(), bogosum/(500000/HZ), (bogosum/(5000/HZ))%100);

That is a complicated question - because linux-next also has patches
by Arjan that
change how (when) cpus are brought online. Initially I blamed his
patches and tried
reverting them ... and saw the symptom you are wondering about (message said
"Total of 1 processors", but the BogoMIPs was a number big enough to be all of
them. Thanks to you, I can now understand why.

Fix will be to stop ia64 from messing directly with cpu_online_map?

-Tony
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