Messages in this thread |  | | Subject | Re: [RESEND PATCH] sched/fair: consider RT/IRQ pressure in select_idle_sibling | From | Rohit Jain <> | Date | Wed, 31 Jan 2018 09:50:56 -0800 |
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On 01/30/2018 05:57 PM, Joel Fernandes wrote:
<snip> >>>> Signed-off-by: Rohit Jain<rohit.k.jain@oracle.com> >>>> --- >>>> 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? >>>
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> 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.
Hope I answered your question.
Thanks, Rohit
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