Re: [PATCH 1/7] sched: Add static_key for asymmetric cpu capacity optimizations

[Peter Zijlstra]

On Fri, Feb 16, 2018 at 05:39:27PM +0000, Quentin Perret wrote:
> AFAIU it should be safe, but without your check you'll have to go through
> cpus_read_lock()/unlock() every time a CPU is hotplugged. There is probably
> no good reason to re-do that again and again if the state of the key
> never changes. I don't know how expensive those lock/unlock operations are,
> but I bet they are more expensive than testing static_branch_unlikely() :)

This is not a performance critical path, more obvious code is more
better.

Also cpus_read_lock() is dirt cheap most of the time.