Messages in this thread | | | Subject | Re: [RESEND PATCH] sched/fair: consider RT/IRQ pressure in select_idle_sibling | From | Rohit Jain <> | Date | Tue, 6 Feb 2018 09:41:58 -0800 |
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On 02/05/2018 10:50 PM, Joel Fernandes wrote: > On Wed, Jan 31, 2018 at 9:50 AM, Rohit Jain <rohit.k.jain@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> >> >> >> >> 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 > here with SIS_PROP set. Do you see a difference in perf when doing the > same approach as you took in select_idle_core?
I didn't see any measurable impact by changing select_idle_core from the above logic to be the same logic as select_idle_cpu. I am OK with either if there are concerns.
Thanks, Rohit
> > Peter, are you with the approach Rohit has adopted to pick best > capacity idle CPU in select_idle_cpu? I guess nr--; will bail out > early if we have SIS_PROP set, incase the scan cost gets too much but > then again we might end scanning too few CPUs. > > thanks, > > - Joel
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