On Sat, 1 Feb 2025 17:31:06 +0100 Mateusz Guzik <mjguzik@xxxxxxxxx> wrote: > It no longer serves any purpose now that the tasklist_lock -> > pidmap_lock ordering got eliminated. Not disabling interrupts may make thing worse. It is a trade off between 'interrupt latency' and 'lock hold time'. If interrupts are disabled then (clearly) they can get delayed because the lock is held. Provided the lock is only held for a short time it probably doesn't matter. Indeed, unless it is the worst one, it probably doesn't matter at all. After all spin locks shouldn't really be held for significant periods. OTOH if the lock doesn't disable interrupts then an interrupt will increase the length of time a lock is held for. This can be significant - and I mean upwards of 1ms. Network interrupts can tale a while - and then the work that is deferred to 'softint' context happens as well (I don't think a spinlock stops the softint code). I've a feeling that unless a spin lock is held for 'far longer than one should ever be held for' then you really want to disable interrupts. In this case if you get a network interrupt + softint while the pidmap_lock is held then all other cpu won't be able to acquire the lock until the network code finishes. The same issue makes futex pretty much useless in anything trying to do audio processing. David
