Spin Loop Hint support: Draft JEP proposal
aph at redhat.com
Wed Oct 7 15:51:39 UTC 2015
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.
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