----- On Jul 13, 2015, at 11:30 AM, Andrew Hunter ahh@xxxxxxxxxx wrote: > On Mon, Jul 13, 2015 at 8:27 AM, Mathieu Desnoyers > <mathieu.desnoyers@xxxxxxxxxxxx> wrote: >> percpu segments will likely not solve everything. I have a use-case >> with dynamically allocated per-cpu ring buffer in user-space (lttng-ust) >> which can be a challenge for percpu segments. Having a fast getcpu() >> is a win in those cases. >> > > Note that percpu segments allow userspace to trivially implement fast getcpu. > > For the record, Paul and I currently think the best solution is percpu > segments + some variant of a restart-sequence API (we'll have a patch > soon.) Although useful in many situations, percpu segments still have some limitations AFAIU: - They are not available on all architectures (very x86-specific), - Some user-space applications already use those segments. So as long as we only target user-space code that does not use GS, and which runs on x86, the percpu segments seems to be a good idea. However, implementing a more general approach for a fast getcpu cache still appears somewhat useful for the general case. Thanks, Mathieu -- Mathieu Desnoyers EfficiOS Inc. http://www.efficios.com -- To unsubscribe from this list: send the line "unsubscribe linux-api" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
