cpuidle: Fix last_residency division
Snooze is a poll idle state in powernv and pseries platforms. Snooze has a timeout so that if a CPU stays in snooze for more than target residency of the next available idle state, then it would exit thereby giving chance to the cpuidle governor to re-evaluate and promote the CPU to a deeper idle state. Therefore whenever snooze exits due to this timeout, its last_residency will be target_residency of the next deeper state. Commit e93e59ce "cpuidle: Replace ktime_get() with local_clock()" changed the math around last_residency calculation. Specifically, while converting last_residency value from nano- to microseconds, it carries out right shift by 10. Because of that, in snooze timeout exit scenarios last_residency calculated is roughly 2.3% less than target_residency of the next available state. This pattern is picked up by get_typical_interval() in the menu governor and therefore expected_interval in menu_select() is frequently less than the target_residency of any state other than snooze. Due to this we are entering snooze at a higher rate, thereby affecting the single thread performance. Fix this by using more precise division via ktime_us_delta(). Fixes: e93e59ce "cpuidle: Replace ktime_get() with local_clock()" Reported-by:Anton Blanchard <anton@samba.org> Bisected-by:
Shilpasri G Bhat <shilpa.bhat@linux.vnet.ibm.com> Signed-off-by:
Shreyas B. Prabhu <shreyas@linux.vnet.ibm.com> Acked-by:
Daniel Lezcano <daniel.lezcano@linaro.org> Acked-by:
Balbir Singh <bsingharora@gmail.com> Signed-off-by:
Rafael J. Wysocki <rafael.j.wysocki@intel.com>
parent
4c2e07c6
Please register or sign in to comment