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

[Keir Fraser <keir.fraser@xxxxxxxxxxxxx>]

On 11/9/08 12:33, "Shan, Haitao" <haitao.shan@xxxxxxxxx> wrote:

> Thanks!
> Concerning cpu online/offline development, I have a small question here.
> Since cpu_online_map is very important, code in different subsystems may use
> it extensively. If such code is not designed with cpu online/offline in mind,
> it may introduce race conditions, just like the one fixed in cpu calibration
> rendezvous.
> Currently, we solve it in a find-and-fix manner. Do you have any idea that can
> solve the problem in a cleaner way?
> Thanks in advance.

Mostly it will be race against CPUs coming online, since stop_machine_run()
is a strong barrier in the offline case. We could use stop_machine_run() for
onlining too (even if just to set a bit in cpu_online_map). Or indeed we
just carry on fixing up the bugs one by one as we find them. I actually
doubt there are that many, so I think this current approach is fine.

 -- Keir



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