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[Xen-devel] Re: [PATCH 1/4] CPU online/offline support in Xen

  • To: "Shan, Haitao" <haitao.shan@xxxxxxxxx>
  • From: Keir Fraser <keir.fraser@xxxxxxxxxxxxx>
  • Date: Wed, 10 Sep 2008 11:43:44 +0100
  • Cc: xen-devel@xxxxxxxxxxxxxxxxxxx
  • Delivery-date: Wed, 10 Sep 2008 03:44:12 -0700
  • List-id: Xen developer discussion <xen-devel.lists.xensource.com>
  • Thread-index: AckSWmKh0QG0bsOOQWqAjPJM8eBXpwA17YJn
  • Thread-topic: [PATCH 1/4] CPU online/offline support in Xen

I feel this is more complicated than it needs to be.

How about clearing VCPUs from the offlined CPU's runqueue from the very end
of __cpu_disable()? At that point all other CPUs are safely in softirq
context with IRQs disabled, and we are running on the correct CPU (being
offlined). We could have a hook into the scheduler subsystem at that point
to break affinities, assign to different runqueues, etc. We would just need
to be careful not to try an IPI. :-) This approach would not need a
cpu_schedule_map (which is really increasing code fragility imo, by creating
possible extra confusion about which cpumask is the wright one to use in a
given situation).

My feeling, unless I've missed something, is that this would make the patch
quite a bit smaller and with a smaller spread of code changes.

 -- Keir

On 9/9/08 09:59, "Shan, Haitao" <haitao.shan@xxxxxxxxx> wrote:

> This patch implements cpu offline feature.
> Best Regards
> Haitao Shan

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