Messages in this thread | | | Subject | Re: [PATCH] sched/fair: Make sched-idle cpu selection consistent throughout | From | Parth Shah <> | Date | Fri, 25 Oct 2019 12:13:27 +0530 |
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Hi Viresh,
On 10/24/19 12:15 PM, Viresh Kumar wrote: > There are instances where we keep searching for an idle CPU despite > having a sched-idle cpu already (in find_idlest_group_cpu(), > select_idle_smt() and select_idle_cpu() and then there are places where > we don't necessarily do that and return a sched-idle cpu as soon as we > find one (in select_idle_sibling()). This looks a bit inconsistent and > it may be worth having the same policy everywhere. > > On the other hand, choosing a sched-idle cpu over a idle one shall be > beneficial from performance point of view as well, as we don't need to > get the cpu online from a deep idle state which is quite a time > consuming process and delays the scheduling of the newly wakeup task. > > This patch tries to simplify code around sched-idle cpu selection and > make it consistent throughout. > > FWIW, tests were done with the help of rt-app (8 SCHED_OTHER and 5 > SCHED_IDLE tasks, not bound to any cpu) on ARM platform (octa-core), and > no significant difference in scheduling latency of SCHED_OTHER tasks was > found. > > Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org> > ---
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> @@ -5755,13 +5749,11 @@ static int select_idle_smt(struct task_struct *p, int target) > for_each_cpu(cpu, cpu_smt_mask(target)) { > if (!cpumask_test_cpu(cpu, p->cpus_ptr)) > continue; > - if (available_idle_cpu(cpu)) > + if (available_idle_cpu(cpu) || sched_idle_cpu(cpu)) > return cpu;
I guess this is a correct approach, but just wondering what if we still keep searching for a sched_idle CPU even though we have found an available_idle CPU?
[...]
Thanks, Parth
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