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

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Date:	Tue, 14 Feb 2012 19:55:36 +1030
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Tony Luck <tony.luck@...il.com>,
	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>
Cc:	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, 13 Feb 2012 13:57:45 -0800, Tony Luck <tony.luck@...il.com> wrote:
> 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?

Yes, and the other architectures.

We're well within reach of removing cpu_*_map now I think.

Cheers,
Rusty.

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