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Subject[tip: sched/core] arm64: defconfig: enable CONFIG_SCHED_SMT
The following commit has been merged into the sched/core branch of tip:

Commit-ID: 6f693dd5be08237b337f557c510d99addb9eb9ec
Gitweb: https://git.kernel.org/tip/6f693dd5be08237b337f557c510d99addb9eb9ec
Author: Valentin Schneider <valentin.schneider@arm.com>
AuthorDate: Thu, 27 Feb 2020 19:14:33
Committer: Ingo Molnar <mingo@kernel.org>
CommitterDate: Fri, 06 Mar 2020 12:57:23 +01:00

arm64: defconfig: enable CONFIG_SCHED_SMT

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
---
arch/arm64/configs/defconfig | 1 +
1 file changed, 1 insertion(+)

diff --git a/arch/arm64/configs/defconfig b/arch/arm64/configs/defconfig
index 905109f..3e75007 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
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