Re: [PATCH] Avoid mask based num_possible_cpus and num_online_cpus-v5

From: Andrew Morton
Date: Thu Feb 02 2012 - 15:19:13 EST

On Fri, 03 Feb 2012 06:33:02 +1030
Rusty Russell <rusty@xxxxxxxxxxxxxxx> wrote:

> On Wed, 1 Feb 2012 14:01:25 -0800, Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> 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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