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The (CFS) scheduler has some extra logic catering to systems with SMT, but that logic won't be compiled in unless the above config is set. Note that the SMT-centric codepaths are gated by the sched_smt_present static key, and the SMT sched_domains will only survive if the platform has SMT. As such, the only impact on !SMT platforms should be a slightly bigger kernel - no behavioural change. Distro kernels already enable it, which makes sense since there already are things like ThunderX2 out in the wild. Enable it for the defconfig. Some deltas =========== FWIW my ELF symbol table diff looks something like this: NAME BEFORE AFTER DELTA update_sd_lb_stats.constprop.135 0 1864 +1864 find_idlest_group.isra.115 0 1808 +1808 update_numa_stats.isra.121 0 628 +628 select_task_rq_fair 3236 3732 +496 compute_energy.isra.112 0 420 +420 score_nearby_nodes.part.120 0 380 +380 __update_idle_core 0 232 +232 nohz_balance_exit_idle.part.127 0 216 +216 sched_slice.isra.99 0 172 +172 update_load_avg.part.107 0 116 +116 wakeup_preempt_entity.isra.101 0 92 +92 sched_cpu_activate 340 396 +56 pick_next_task_idle 8 56 +48 sched_cpu_deactivate 252 292 +40 show_smt_active 44 80 +36 cpu_smt_mask 0 28 +28 set_next_task_idle 4 32 +28 task_numa_work 680 692 +12 cpu_smt_flags 0 8 +8 enqueue_task_fair 2608 2612 +4 wakeup_preempt_entity.isra.104 92 0 -92 update_load_avg 1028 932 -96 task_numa_migrate 1824 1728 -96 sched_slice.isra.102 172 0 -172 nohz_balance_exit_idle.part.130 216 0 -216 task_numa_find_cpu 2116 1868 -248 score_nearby_nodes.part.123 380 0 -380 compute_energy.isra.115 420 0 -420 update_numa_stats.isra.124 472 0 -472 find_idlest_group.isra.118 1808 0 -1808 update_sd_lb_stats.constprop.138 1864 0 -1864 ------------------------------------------------------------------ DELTA SUM +820 As for the sched_domains, this is on a hikey960: before: $ cat /proc/sys/kernel/sched_domain/cpu*/domain*/name | sort | uniq DIE MC after: $ cat /proc/sys/kernel/sched_domain/cpu*/domain*/name | sort | uniq DIE MC Reviewed-by: Dietmar Eggemann <dietmar.eggemann@arm.com> Signed-off-by: Valentin Schneider <valentin.schneider@arm.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Signed-off-by: Ingo Molnar <mingo@kernel.org> Link: https://lkml.kernel.org/r/20200227191433.31994-3-valentin.schneider@arm.com |
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