On Mon, Feb 5, 2018 at 10:50 PM, Joel Fernandes <joe...@google.com> wrote: > On Wed, Jan 31, 2018 at 9:50 AM, Rohit Jain <rohit.k.j...@oracle.com> wrote: >>>>>> kernel/sched/fair.c | 38 ++++++++++++++++++++++++++++---------- >>>>>> 1 file changed, 28 insertions(+), 10 deletions(-) >>>>>> >>>>>> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c >>>>>> index 26a71eb..ce5ccf8 100644 >>>>>> --- a/kernel/sched/fair.c >>>>>> +++ b/kernel/sched/fair.c >>>>>> @@ -5625,6 +5625,11 @@ static unsigned long capacity_orig_of(int cpu) >>>>>> return cpu_rq(cpu)->cpu_capacity_orig; >>>>>> } >>>>>> >>>>>> +static inline bool full_capacity(int cpu) >>>>>> +{ >>>>>> + return capacity_of(cpu) >= (capacity_orig_of(cpu)*3)/4; >>>>>> +} >>>>>> + >>>>>> static unsigned long cpu_avg_load_per_task(int cpu) >>>>>> { >>>>>> struct rq *rq = cpu_rq(cpu); >>>>>> @@ -6081,7 +6086,7 @@ static int select_idle_core(struct task_struct >>>>>> *p, >>>>>> struct sched_domain *sd, int >>>>>> >>>>>> for_each_cpu(cpu, cpu_smt_mask(core)) { >>>>>> cpumask_clear_cpu(cpu, cpus); >>>>>> - if (!idle_cpu(cpu)) >>>>>> + if (!idle_cpu(cpu) || !full_capacity(cpu)) >>>>>> idle = false; >>>>>> } >>>>> >>>>> There's some difference in logic between select_idle_core and >>>>> select_idle_cpu as far as the full_capacity stuff you're adding goes. >>>>> In select_idle_core, if all CPUs are !full_capacity, you're returning >>>>> -1. But in select_idle_cpu you're returning the best idle CPU that's >>>>> the most cap among the !full_capacity ones. Why there is this >>>>> different in logic? Did I miss something? >>>>> >> >> <snip> >> >>> Dude :) That is hardly an answer to the question I asked. Hint: >>> *different in logic*. >> >> >> Let me re-try :) >> >> For select_idle_core, we are doing a search for a fully idle and full >> capacity core, the fail-safe is select_idle_cpu because we will re-scan >> the CPUs. The notion is to select an idle CPU no matter what, because >> being on an idle CPU is better than waiting on a non-idle one. In >> select_idle_core you can be slightly picky about the core because >> select_idle_cpu is a fail safe. I measured the performance impact of >> choosing the "best among low cap" vs the code changes I have (for >> select_idle_core) and could not find a statistically significant impact, >> hence went with the simpler code changes. > > That's Ok with me. Just that I remember Peter messing with this path > and that it was expensive to scan too much for some systems. The other > thing is you're really doing to do a "fail safe" as you call it search
I meant to say here, "you're NOT really going to be doing a 'fail safe' search here as you call it" thanks, - Joel