Messages in this thread | | | From | Vincent Guittot <> | Date | Wed, 9 Oct 2019 13:34:06 +0200 | Subject | Re: [RFC v5 4/6] sched/fair: Tune task wake-up logic to pack small background tasks on fewer cores |
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On Wed, 9 Oct 2019 at 11:23, Parth Shah <parth@linux.ibm.com> wrote: > > > > On 10/8/19 6:58 PM, Hillf Danton wrote: > > > > On Mon, 7 Oct 2019 14:00:49 +0530 Parth Shah wrote: > >> +/* > >> + * Try to find a non idle core in the system based on few heuristics: > >> + * - Keep track of overutilized (>80% util) and busy (>12.5% util) CPUs > >> + * - If none CPUs are busy then do not select the core for task packing > >> + * - If atleast one CPU is busy then do task packing unless overutilized CPUs > >> + * count is < busy/2 CPU count > >> + * - Always select idle CPU for task packing > >> + */ > >> +static int select_non_idle_core(struct task_struct *p, int prev_cpu, int target) > >> +{ > >> + struct cpumask *cpus = this_cpu_cpumask_var_ptr(turbo_sched_mask); > >> + int iter_cpu, sibling; > >> + > >> + cpumask_and(cpus, cpu_online_mask, p->cpus_ptr); > >> + > >> + for_each_cpu_wrap(iter_cpu, cpus, prev_cpu) { > >> + int idle_cpu_count = 0, non_idle_cpu_count = 0; > >> + int overutil_cpu_count = 0; > >> + int busy_cpu_count = 0; > >> + int best_cpu = iter_cpu; > >> + > >> + for_each_cpu(sibling, cpu_smt_mask(iter_cpu)) { > >> + __cpumask_clear_cpu(sibling, cpus); > >> + if (idle_cpu(iter_cpu)) { > > > > Would you please elaborate the reasons that the iter cpu is checked idle > > more than once for finding a busy core? > > > > Thanks for looking at the patches. > Could you please point me out where iter_cpu is checked more than once?
I think that point is that you have a sibling that there is for_each_cpu(sibling, cpu_smt_mask(iter_cpu) but you never use sibling in the loop except for clearing it on the cpumask cpus All the tests are done with iter_cpu so you will test several time iter_cpus but never the other sibling Should you use sibling instead ?
> > >> + idle_cpu_count++; > >> + best_cpu = iter_cpu; > >> + } else { > >> + non_idle_cpu_count++; > >> + if (cpu_overutilized(iter_cpu)) > >> + overutil_cpu_count++; > >> + if (is_cpu_busy(cpu_util(iter_cpu))) > >> + busy_cpu_count++; > >> + } > >> + } > >> + > > >
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