* Manfred Spraul <manfred@xxxxxxxxxxxxxxxx> wrote: > 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(). Technically you could use spin_trylock()+spin_unlock() and avoid the lock acquire spinning on spin_unlock() and get very close to the slow path performance of a pure cacheline-dirtying behavior. But adding something like spin_barrier(), which purely dirties the lock cacheline, would be even faster, right? Thanks, Ingo -- To unsubscribe from this list: send the line "unsubscribe netfilter-devel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
