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SubjectRe: [discuss] Re: [patch 0/4] CPU hot-plug support for x86_64
On Mon, May 23, 2005 at 07:12:12PM +0200, Andi Kleen wrote:
> > The only other workable alternate would be to use the stop_machine()
> > like thing which we use to automically update cpu_online_map. This means we
> > execute a high priority thread on all cpus, bringing the system to knees before
>
> That is not nice agreed.
>
> > just adding a new cpu. On very large systems this will definitly be
> > visible.
>
> I still dont quite get it why it is not enough to keep interrupts
> off until the CPU enters idle. Currently we enable them shortly
> in the middle of the initialization (whcih is already dangerous
> because interrupts can see half initialized state like out of date TSC),
> but I hope to get rid of that soon too. With the full startup
> in CLI would you problems be gone?
>

I think so, if we can ensure none is delivered to the partially up cpu
we probably are covered.

Iam not a 100% sure about above either, if the smp_call_function
is started with 3 cpus initially, and 1 just came up, the counts in
the smp_call data struct could be set to 3 as a result of the new cpu
received this broadcast as well, and we might quit earlier in the wait.

sending to only relevant cpus removes that ambiquity.

[Vatsa would know this better, since was the corner case man then :-)]
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