linux-kernel - Re: [PATCH 1/6] genirq: allow assigning affinity to present but not online CPUs

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Date:   Sun, 5 Feb 2017 17:40:23 +0100
From:   Christoph Hellwig <hch@....de>
To:     Joe Korty <joe.korty@...r.com>
Cc:     Christoph Hellwig <hch@....de>,
        Keith Busch <keith.busch@...el.com>,
        linux-nvme@...ts.infradead.org, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/6] genirq: allow assigning affinity to present but
        not online CPUs

Hi Joe,

On Fri, Feb 03, 2017 at 08:58:09PM -0500, Joe Korty wrote:
> IIRC, some years ago I ran across a customer system where
> the #cpus_present was twice as big as #cpus_possible.
> 
> Hyperthreading was turned off in the BIOS so it was not
> entirely out of line for the extra cpus to be declared
> present, even though none of them would ever be available
> for use.

This sounds like a system we should quirk around instead of optimizing
for it.  Unless I totally misunderstand the idea behind cpu_possible
and cpu_present.