On 2018.10.02 14:51 Rafael J. Wysocki wrote: > From: Rafael J. Wysocki <rafael.j.wyso...@intel.com> > > If need_resched() returns "false", breaking out of the loop in > poll_idle() will cause a new idle state to be selected, so in fact > usually it doesn't make sense to spin in it longer than the target > residency of the second state. [Note that the "polling" state is > used only if there is at least one "real" state defined in addition > to it.] On the other hand, breaking out of it early (say in case > the next state is disabled) shouldn't hurt as it is polling anyway.
While I agree that it is polling anyway, this change can add significant burden when debugging and trace is enabled for cpu_idle, if idle state 0 is used often. For example: Phoronix dbench test, 96 clients: 900 second trace: Kernel 4.20-rc1: idle state 0 entry exits: 686,724 Does trace being enabled effect the system under test: Yes. Kernel 4.20-rc1 with this patch reverted: idle state 0 entry exits: 66,185 Does trace being enabled effect the system under test: No, or minimal. ... Doug
