Re: [PATCH 2/2] x86: implement multiple queues for smp function call IPIs

[Andi Kleen <andi@firstfloor.org>]

> So ... how about my original suggestion, to add a (default-off) boot 
> option that reduces the queues to 1? I.e. lets have something in place 
> from day 1 on that could be quirk-handler-driven, should the need arise. 
> "apic=simpleipi" or something like that.
> 
> In a year or two, once this all has proven itself fine on a broad range 
> of systems, we'll laugh out loud at being so cautious and can remove the 
> boot option for good ;-)

I agree that adding a boot option to turn it off is a good idea (assuming
it doesn't take too much code to implement) Adding such paranoid boot options early 
has saved my ass a few times in the past.

Only tricky bit is use if () not "modulo variable", because the if ()
will be much faster than a division through an arbitary number.

-Andi