Hi Ingo,

On 07/07/2017 10:31 AM, Ingo Molnar wrote:

There's another, probably just as significant advantage: queued_spin_unlock_wait()
is 'read-only', while spin_lock()+spin_unlock() dirties the lock cache line. On
any bigger system this should make a very measurable difference - if
spin_unlock_wait() is ever used in a performance critical code path.

At least for ipc/sem:
Dirtying the cacheline (in the slow path) allows to remove a smp_mb() in 
the hot path.
So for sem_lock(), I either need a primitive that dirties the cacheline 
or sem_lock() must continue to use spin_lock()/spin_unlock().

--
     Manfred