On Thu, 7 Nov 2024, Ankur Arora wrote: > > Calling the clock retrieval function repeatedly should be fine and is > > typically done in user space as well as in kernel space for functions that > > need to wait short time periods. > > The problem is that you might have multiple CPUs polling in idle > for prolonged periods of time. And, so you want to minimize > your power/thermal envelope. On ARM that maps to YIELD which does not do anything for the power envelope AFAICT. It switches to the other hyperthread. > For instance see commit 4dc2375c1a4e "cpuidle: poll_state: Avoid > invoking local_clock() too often" which originally added a similar > rate limit to poll_idle() where they saw exactly that issue. Looping w/o calling local_clock may increase the wait period etc. For power saving most arches have special instructions like ARMS WFE/WFET. These are then causing more accurate wait times than the looping thing?
