Re: [PATCH 0/3] task: Making tasks on the runqueue rcu protected

From: Peter Zijlstra
Date: Tue Sep 03 2019 - 15:47:01 EST

On Tue, Sep 03, 2019 at 08:44:40AM -0700, Linus Torvalds wrote:

> That said, it won't affect any of the core architectures much, because
> smp_store_release() isn't that expensive (it's just a compiler barrier
> on x86, it's a cheap instruction on arm64, and it should be very cheap
> on any other architecture too unless they do insane things - even on
> powerpc, which is about the worst case for any barriers, it's just an
> lwsync).

Right, x86/s390/Sparc it's a compiler barrier, ARM64 has a store-release
op which is relatively cheap, Power has an LWSYNC, but the rest does
store-release with smp_mb() -- and this includes ARM.