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 next deeper state.
commit e93e59ce5b85 ("cpuidle: Replace ktime_get() with local_clock()") changed the math around last_residency calculation. Specifically, while converting last_residency value from nanoseconds to microseconds it does right shift by 10. Due to this, in snooze timeout exit scenarios last_residency calculated is roughly 2.3% less than target_residency of next available state. This pattern is picked up get_typical_interval() in the menu governor and therefore expected_interval in menu_select() is frequently less than the target_residency of any state but snooze. Due to this we are entering snooze at a higher rate, thereby affecting the single thread performance. Fix this by replacing right shift by 10 with /1000 while calculating last_residency. Reported-by: Anton Blanchard <an...@samba.org> Bisected-by: Shilpasri G Bhat <shilpa.b...@linux.vnet.ibm.com> Signed-off-by: Shreyas B. Prabhu <shre...@linux.vnet.ibm.com> --- Changes in v2 ============= - Fixing it in the cpuidle core code instead of driver code. drivers/cpuidle/cpuidle.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/drivers/cpuidle/cpuidle.c b/drivers/cpuidle/cpuidle.c index a4d0059..30d67a8 100644 --- a/drivers/cpuidle/cpuidle.c +++ b/drivers/cpuidle/cpuidle.c @@ -218,10 +218,10 @@ int cpuidle_enter_state(struct cpuidle_device *dev, struct cpuidle_driver *drv, local_irq_enable(); /* - * local_clock() returns the time in nanosecond, let's shift - * by 10 (divide by 1024) to have microsecond based time. + * local_clock() returns the time in nanosecond, let's + * divide by 1000 to have microsecond based time. */ - diff = (time_end - time_start) >> 10; + diff = (time_end - time_start) / 1000; if (diff > INT_MAX) diff = INT_MAX; -- 2.1.4 _______________________________________________ Linuxppc-dev mailing list Linuxppc-dev@lists.ozlabs.org https://lists.ozlabs.org/listinfo/linuxppc-dev