Re: [PATCH 5/6] powerpc/mm: Optimize detection of thread local mm's

On Mon, 2017-07-24 at 21:25 +1000, Nicholas Piggin wrote:

quoted

+#ifdef CONFIG_PPC_BOOK3S_64
+static inline void inc_mm_active_cpus(struct mm_struct *mm)
+{
+     atomic_inc(&mm->context.active_cpus);
+}
+#else
+static inline void inc_mm_active_cpus(struct mm_struct *mm) { }
+#endif

This is a bit awkward. Can we just move the entire function to test
cpumask and set / increment into helper functions and define them
together with mm_is_thread_local, so it's all in one place?

I thought about it but then we have 2 variants, unless I start moving
the active_cpus into mm_context_t on all the 32-bit subarchs too, etc..

It gets messy either way.

The extra atomic does not need to be defined when it's not used either.

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?

Right, we could.

Looks like a good optimisation though.

Thx. It's a pre-req for further optimizations such as flushing the PID
when a single threaded process moves, so we don't have to constantly
scan the mask.

Cheers,
Ben.