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

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Date:	Thu, 2 Feb 2012 12:19:12 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Rusty Russell <rusty@...tcorp.com.au>
Cc:	Venkatesh Pallipadi <venki@...gle.com>,
	KOSAKI Motohiro <kosaki.motohiro@...il.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Mike Travis <travis@....com>,
	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.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 Fri, 03 Feb 2012 06:33:02 +1030
Rusty Russell <rusty@...tcorp.com.au> wrote:

> On Wed, 1 Feb 2012 14:01:25 -0800, Andrew Morton <akpm@...ux-foundation.org> wrote:
> > > Though most of the callers of these two routines are init time (with few
> > > exceptions of runtime calls), it is cleaner to use variables
> > > and not go through this repeated mask based calculation.
> > 
> > Looks good to me.
> 
> But, I wonder who's asking num_possible_cpus().  It's not a very useful
> thing to know, though some arch's "know" it's contiguous, so can cheat.
> 
> Optimizing it seems particularly foolish.

We're fools for optimisations!

> We either audit and wean
> everyone off who's using it incorrectly, or insist on contiguous CPU
> numbers and drop the mask altogether.

drivers/block/nvme.c looks like it's assuming a contiguous map.  Maybe
also drivers/scsi/bnx2fc (wtf?).  I didn't see anything else outside
arch code.

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