Re: <PING> Re: [patch x86/core] x86: allow number of additionalhotplug CPUs to be set at compile time

[Thomas Gleixner]

On Sun, 5 Oct 2008, Ingo Molnar wrote:
> 
> * Thomas Gleixner <tglx@xxxxxxxxxxxxx> wrote:
> 
> > On Sun, 5 Oct 2008, Ingo Molnar wrote:
> > > * Chuck Ebbert <cebbert@xxxxxxxxxx> wrote:
> > > 
> > > > Yes, it works and I don't see how it could cause any problems.
> > > > 
> > > > Ingo, can we get this in 2.6.27? You can drop my original patch.
> > > > 
> > > > Tested-by: Chuck Ebbert <cebbert@xxxxxxxxxx>
> > > 
> > > looks good, applied to tip/x86/core, thanks!
> > 
> > No, this patch is horrible. 
> > 
> > The correct check is num_present_cpus(). There is no need to make the 
> > weird additional_cpus hackery globally available.
> 
> ah, indeed!
> 
> applied to tip/x86/core and i've zapped Andi's patch.
> 
> > Btw, additional_cpus has interesting properties. Providing a negative 
> > number < -1 on the kernel command line - happened due to a typo - 
> > explodes in early boot, which is not really surprising, but should be 
> > sanity checked.
> 
> indeed, and that mess was introduced, interestingly, by this commit, 
> three years ago, by Andi:
> 
> | From 420f8f68c9c5148dddf946bebdbc7eacde2172cb Mon Sep 17 00:00:00 2001
> | From: Andi Kleen <ak@xxxxxxx>
> | Date: Sat, 5 Nov 2005 17:25:54 +0100
> | Subject: [PATCH] [PATCH] x86_64: New heuristics to find out hotpluggable CPUs.
> 
> so to clean up the mess i've removed the additional_cpus= boot parameter 
> and the Kconfig entry as well - see the patch in x86/core below.
> 
> thanks Thomas for decoding this ...
> 
> and no way can any of this go into v2.6.27: this is fragile code with a 
> lot of historic baggage and the original error is non-fatal to begin 
> with. It can easily be backported to .27.1 if testing shows that it has 
> no other adverse side-effects.

Please lets get rid of all this.

Thanks,

	tglx
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