Re: [discuss] Re: [patch 0/4] CPU hot-plug support for x86_64

[Ashok Raj <ashok.raj@intel.com>]

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 because interrupts can see half initialized state like out of date TSC),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 :-)]