linux-kernel - Re: [PATCH] Correct nr_processes() when CPUs have been unplugged

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Message-ID: <alpine.LFD.2.01.0911030748430.31845@localhost.localdomain>
Date:	Tue, 3 Nov 2009 07:51:25 -0800 (PST)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Ian Campbell <Ian.Campbell@...rix.com>
cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Rusty Russell <rusty@...tcorp.com.au>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] Correct nr_processes() when CPUs have been unplugged



On Tue, 3 Nov 2009, Ian Campbell wrote:
> 
> Therefore calculating the sum of process_counts over only the online
> CPUs omits the processes which were started or stopped on any CPU which
> has since been unplugged. Only the sum of process_counts across all
> possible CPUs has meaning.

I think your patch is fine, but I also suspect that we could/should 
instead fix it by doing something like

	per_cpu(process_counts, this_cpu) += per_cpu(process_counts, down_cpu);
	per_cpu(process_counts, down_cpu) = 0;

in the CPU off-lining case after having quieted 'down_cpu'. That way we 
could always use online CPU's rather than possible CPU's. I think that 
just sounds nicer.

So I'll apply the patch, but I get the feeling it could be done better.

		Linus
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