On Fri, Aug 19, 2016 at 01:23:57PM -0700, Linus Torvalds wrote: > On Fri, Aug 19, 2016 at 1:07 PM, Mathieu Desnoyers > <mathieu.desnoy...@efficios.com> wrote: > > > > Benchmarking various approaches for reading the current CPU number: > > So I'd like to see the benchmarks of something that actually *does* something. > > IOW, what's the bigger-picture "this is what it actually is useful > for, and how it speeds things up". > > Nobody gets a cpu number just to get a cpu number - it's not a useful > thing to benchmark. What does getcpu() so much that we care?
The combination of CPU number and restartable sequence allows userspace to write "per-CPU" rather than "per-thread" algorithms, just as the kernel can. The kernel can do that with preempt_disable(). Userspace can do it with "tell me my CPU and restart me if preempted". But yes, this needs a benchmark of, for instance, urcu implemented on top of this, or some concrete data structure.
