Re: [RFC] CPUMASK: proposal for replacing cpumask_t

[H. Peter Anvin]

Mike Travis wrote:
> Here's the thread:
>
> 	http://marc.info/?l=linux-kernel&m=121976977901223&w=4
>
> It doesn't seem worthwhile to force all systems to deal with large cpumask's
> if they don't need to.  Passing the value on the stack (actually usually in a
> reg) if it fits into a long makes a lot of sense.
>
> And I don't think it's that abstract, but I'm willing to hear other opinions.
>
> Btw, most likely only distros that distribute an "Enterprise" edition of
> Linux will ever set NR_CPUS so high, so the actual number of systems making
> use of this will be a very small percentage (big $$-wise though... ;-) 
>
> I even think that perhaps BITS_PER_LONG might be too low a threshold to kick
> in this extra code.  A Larabee chip will have 128 cpus so maybe 128 or 256 is
> a better metric...?
>
> As soon as I get a working kernel with the proposed changes, I will definitely
> be doing perf testing.

If the performance difference isn't significant, then there is a major 
advantage to getting rid of a configuration option.  At that point we 
can basically scale to an arbitrary number of processors in a stock 
configuration.

	-hpa

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