On 06.03.23 15:20, Paolo Bonzini wrote:
On 3/6/23 14:31, David Hildenbrand wrote:- smp_mb_acquire(); - if (value == EV_SET) { - /* If there was a concurrent reset (or even reset+wait), - * do nothing. Otherwise change EV_SET->EV_FREE. - */ - qatomic_or(&ev->value, EV_FREE); - } +[had the same thought on patch #2] IIUC, the "read first" is an optimization to not unconditionally dirty the cache-line. But I assume we don't particularly care about that optimization on the reset path.Thinking more about it, the intended usage of QemuEvent is either qemu_event_reset(); if (!check()) { qemu_event_wait()); } or if (!check()) { qemu_event_reset(); if (!check()) { qemu_event_wait()); } } If we don't care on the reset path we care much less on the wait path. Should I remove it and go straight to the cmpxchg, just for peace of mind?
Sounds reasonable to me at could simplify qemu_event_wait a bit. -- Thanks, David / dhildenb
