On Tue, Jul 27, 2021 at 10:29:59AM +0800, Boqun Feng wrote:

quoted

"How to implement xchg_tail" shouldn't force with _Q_PENDING_BITS, but
the arch could choose.

I actually agree with this part, but this patchset failed to provide
enough evidences on why we should choose xchg_tail() implementation
based on whether hardware has xchg16, more precisely, for an archtecture
which doesn't have a hardware xchg16, why cmpxchg emulated xchg16() is
worse than a "load+cmpxchg) implemeneted xchg_tail()? If it's a
performance reason, please show some numbers.

Right. Their problem is their broken xchg16() implementation.