On 7/6/19 1:06 PM, Rafael J. Wysocki wrote:
The patch is below, but note that it adds the tick stopping overhead to the idle loop for CPUs that are not adaptive-tick and when PM QoS latency constraints are used which is not desirable in general.Please test it, but as I said above, the real solution appears to be to treat adaptive-tick CPUs in a special way in the idle loop. --- drivers/cpuidle/governors/menu.c | 16 +++++----------- 1 file changed, 5 insertions(+), 11 deletions(-) Index: linux-pm/drivers/cpuidle/governors/menu.c =================================================================== --- linux-pm.orig/drivers/cpuidle/governors/menu.c +++ linux-pm/drivers/cpuidle/governors/menu.c @@ -302,9 +302,10 @@ static int menu_select(struct cpuidle_dr !drv->states[0].disabled && !dev->states_usage[0].disable)) { /* * In this case state[0] will be used no matter what, so return - * it right away and keep the tick running. + * it right away and keep the tick running if state[0] is a + * polling one. */ - *stop_tick = false; + *stop_tick = !!(drv->states[0].flags & CPUIDLE_FLAG_POLLING); return 0; }@@ -395,16 +396,9 @@ static int menu_select(struct cpuidle_dr return idx;} - if (s->exit_latency > latency_req) { - /* - * If we break out of the loop for latency reasons, use - * the target residency of the selected state as the - * expected idle duration so that the tick is retained - * as long as that target residency is low enough. - */ - predicted_us = drv->states[idx].target_residency; + if (s->exit_latency > latency_req) break; - } + idx = i; }
I tested the patch and it appears to work. Idle CPUs now have ticks disabled even when /dev/cpu_dma_latency is used. I also want to thank you for your work on the idle loop redesign. Overall it works much better than before. I used to have a problem where idle CPUs would end up doing C0 polling for a long time resulting in a big performance drop on the HT sibling. When benchmarking I always had to offline siblings to get consistent results. That problem was fixed in the redesign.
