Feature #17566

Tune thread QoS / efficiency on macOS

Added by mperham (Mike Perham) about 2 months ago. Updated about 1 month ago.

Target version:


Hi, new Apple M1 processors have "performance" and "efficiency" cores. Apple provides a QoS API so threads can tune which cores they should execute on. Some threads should be executed as high-priority, some should be treated as low-priority.

This page shows the pthread APIs that Apple provides:

pthread_set_qos_class_self_np(QOS_CLASS_BACKGROUND, 0)

I noticed Ruby already provides Thread#priority= which says This is just hint for Ruby thread scheduler. It may be ignored on some platform. Does this API work still or was it only active for Ruby 1.8's green threads? Should this API use the QoS APIs on macOS?

Updated by ko1 (Koichi Sasada) about 1 month ago

Actually, Thread#priority is not tested.
I'm not sure we can use this pthread_set_qos_class_self_np API for priority because it accepts an integer and there is no agreement which number is "high" and "low". Introducing another API makes sense more for me. But I'm also not sure we can introduce a new API only for Mac OS.

Also I'm not sure pthread_set_qos_class_self_np is needed for Ruby users (I think Mac OS will choose good core than a programmer, I guess).

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