Re: [PATCH v2 3/5] locking/qspinlock: Introduce CNA into the slow path of qspinlock

[Peter Zijlstra <peterz@infradead.org>]

On Wed, Apr 03, 2019 at 12:33:20PM -0400, Waiman Long wrote:
> static inline void queued_spin_lock_slowpath(struct qspinlock *lock, u32
> val)
> {
>         if (static_branch_unlikely(&use_numa_spinlock))
>                 numa_queued_spin_lock_slowpath(lock, val);
>         else   
>                 native_queued_spin_lock_slowpath(lock, val);
> }

That's horrible for the exact reason you state.

> Alternatively, we can also call numa_queued_spin_lock_slowpath() in
> native_queued_spin_lock_slowpath() if we don't want to increase the code
> size of spinlock call sites.

Yeah, still don't much like that though, we're littering the fast path
of that slow path with all sorts of crap.