On 07/17/2014 11:26 AM, Christoph Lameter wrote: > On Thu, 17 Jul 2014, Pranith Kumar wrote: > >> I can mention that IPI is preferable. What is that you don't want mentioned? >> atomic_t? > > Definitely not as an example. atomic_t in per cpu areas is self > contradicting. The per cpu area is exclusively for that processor whereas > an atomic_t is supposed to be accessed from multiple processors. > >>> Remote percpu updates are extremely rare events. If the cpu is idle/asleep >>> then usually no updates are needed because no activity is occurring on >>> that cpu. >>> >> >> Yes, -usually- that is the case. But we are talking about the extreme rare >> event >> where we need to update some remote CPU`s per-cpu data without waking it up >> from >> sleep/idle. How do you suggest we handle this? I don't think suggesting not >> to >> use per-cpu areas because of this is a good idea, since we lose a lot of >> performance in the most common cases. > > If you modify a percpu area then that is usually done because that cpu > needs to take some action. An IPI is fine. > > Otherwise yes I would suggest not use a percpu area but a separate data > structure for synchronization. >
Yes, I will add this information to the doc. Thanks! -- Pranith -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
