On Tue, Jan 30, 2018 at 11:47 AM, Rohit Jain <rohit.k.j...@oracle.com> wrote: [...] >>> @@ -6102,7 +6107,8 @@ static int select_idle_core(struct task_struct *p, >>> struct sched_domain *sd, int >>> */ >>> static int select_idle_smt(struct task_struct *p, struct sched_domain >>> *sd, int target) >>> { >>> - int cpu; >>> + int cpu, rcpu = -1; >>> + unsigned long max_cap = 0; >>> >>> if (!static_branch_likely(&sched_smt_present)) >>> return -1; >>> @@ -6110,11 +6116,13 @@ static int select_idle_smt(struct task_struct *p, >>> struct sched_domain *sd, int t >>> for_each_cpu(cpu, cpu_smt_mask(target)) { >>> if (!cpumask_test_cpu(cpu, &p->cpus_allowed)) >>> continue; >>> - if (idle_cpu(cpu)) >>> - return cpu; >>> + if (idle_cpu(cpu) && (capacity_of(cpu) > max_cap)) { >>> + max_cap = capacity_of(cpu); >>> + rcpu = cpu; >> >> At the SMT level, do you need to bother with choosing best capacity >> among threads? If RT is eating into one of the SMT thread's underlying >> capacity, it would eat into the other's. Wondering what's the benefit >> of doing this here. > > > Yes, you are right because of SD_SHARE_CPUCAPACITY, however the benefit > is that if don't do this check, we might end up picking a SMT thread > which has "high" RT/IRQ activity and be on the run queue for a while, > till the pull side can bail us out.
Do your tests show a difference in results though with such change (for select_idle_smt)? thanks, - Joel