Spin Loop Hint support: Draft JEP proposal (original) (raw)

Andrew Haley 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.

Andrew.

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