Re: [RFC PATCH v8 1/9] Restartable sequences system call

On Fri, Aug 19, 2016 at 01:23:57PM -0700, Linus Torvalds wrote:

On Fri, Aug 19, 2016 at 1:07 PM, Mathieu Desnoyers
[off-list ref] wrote:

quoted

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.