Nicholas Piggin [off-list ref] writes:

On Mon, 24 Jul 2017 23:46:44 +1000
Michael Ellerman [off-list ref] wrote:

quoted

Nicholas Piggin [off-list ref] writes:

quoted

On Mon, 24 Jul 2017 14:28:02 +1000
Benjamin Herrenschmidt [off-list ref] wrote:
 

quoted

Instead of comparing the whole CPU mask every time, let's
keep a counter of how many bits are set in the mask. Thus
testing for a local mm only requires testing if that counter
is 1 and the current CPU bit is set in the mask.  

...

quoted

Also does it make sense to define it based on NR_CPUS > BITS_PER_LONG?
If it's <= then it should be similar load and compare, no?  

Do we make a machine with that few CPUs? ;)

I don't think it's worth special casing, all the distros run with much
much larger NR_CPUs than that.

Not further special-casing, but just casing it based on NR_CPUS
rather than BOOK3S.

The problem is the mm_context_t is defined based on BookE vs BookS etc.
not based on NR_CPUS.

So we'd have to add the atomic_t to all mm_context_t's, but #ifdef'ed
based on NR_CPUS.

But then some platforms don't support SMP, so it's a waste there. The
existing cpumask check compiles to ~= nothing on UP.

cheers