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Date: Tue, 25 Jul 2017 10:34:39 +1000
From: Nicholas Piggin <npiggin@gmail.com>
To: Michael Ellerman <mpe@ellerman.id.au>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>,
 linuxppc-dev@lists.ozlabs.org, aneesh.kumar@linux.vnet.ibm.com
Subject: Re: [PATCH 5/6] powerpc/mm: Optimize detection of thread local mm's
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On Mon, 24 Jul 2017 23:46:44 +1000
Michael Ellerman <mpe@ellerman.id.au> wrote:

> Nicholas Piggin <npiggin@gmail.com> writes:
> 
> > On Mon, 24 Jul 2017 14:28:02 +1000
> > Benjamin Herrenschmidt <benh@kernel.crashing.org> wrote:
> >  
> >> 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.  
> ...
> >
> > 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.

Thanks,
Nick