| Message ID | 20200226164118.6405-3-valentin.schneider@arm.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | sched, arm64: enable CONFIG_SCHED_SMT for arm64 | expand |
On 26.02.20 16:41, Valentin Schneider wrote: > 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. [...] > > 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 Have you tested that EAS still comes up ?
On Thu, Feb 27 2020, Dietmar Eggemann wrote: >> 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 > > Have you tested that EAS still comes up ? Yep: root@valsch-h960:~# zcat /proc/config.gz | grep SMT CONFIG_SCHED_SMT=y root@valsch-h960:~# ./set_governor.sh schedutil [ 127.834363] root_domain 0-7: pd4:{ cpus=4-7 nr_cstate=5 } pd0:{ cpus=0-3 nr_cstate=5 } [ 127.842344] sched_energy_set: starting EAS No reason for it not to come up unless something's broken (but it's always good to check!).
diff --git a/arch/arm64/configs/defconfig b/arch/arm64/configs/defconfig index 905109f6814f..3e75007f6592 100644 --- a/arch/arm64/configs/defconfig +++ b/arch/arm64/configs/defconfig @@ -62,6 +62,7 @@ CONFIG_ARCH_ZX=y CONFIG_ARCH_ZYNQMP=y CONFIG_ARM64_VA_BITS_48=y CONFIG_SCHED_MC=y +CONFIG_SCHED_SMT=y CONFIG_NUMA=y CONFIG_SECCOMP=y CONFIG_KEXEC=y
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 Signed-off-by: Valentin Schneider <valentin.schneider@arm.com> --- arch/arm64/configs/defconfig | 1 + 1 file changed, 1 insertion(+)