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

From: Linus Torvalds
Date: Tue Nov 03 2009 - 10:52:20 EST

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.

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