Spin Loop Hint support: Draft JEP proposal

[Andrew Haley]

On 10/07/2015 04:45 PM, Gil Tene wrote:

> For ARM, I expect WFE/SEV to need to evolve as well, and for other
> reasons, even fit use within OSs. The current WFE/SEV scheme is not
> scalable. While it probably works ok for spinning at the kernel
> level on hardware that only has s handful of cores, the fact that
> the event WFE waits for (and SEV sends) is global to the system will
> break things as core counts grow (it is the hardware equivalent of
> wait/notifyAll() with a single global monitor).

That's not how it works.  It's sufficient to write to the lock word to
wake a core from a WFE: SEV is not required.  Each core has its own
event monitor, and wakeup is handled by the cache coherency logic.

Andrew.