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Subject[PATCH v2 1/2] sched/topology: Don't enable EAS on SMT systems
Date
EAS already requires asymmetric CPU capacities to be enabled, and mixing
this with SMT is an aberration, but better be safe than sorry.

Signed-off-by: Valentin Schneider <valentin.schneider@arm.com>
Acked-by: Quentin Perret <qperret@google.com>
Reviewed-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
---
kernel/sched/topology.c | 12 ++++++++++--
1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c
index 00911884b7e7..8344757bba6e 100644
--- a/kernel/sched/topology.c
+++ b/kernel/sched/topology.c
@@ -317,8 +317,9 @@ static void sched_energy_set(bool has_eas)
* EAS can be used on a root domain if it meets all the following conditions:
* 1. an Energy Model (EM) is available;
* 2. the SD_ASYM_CPUCAPACITY flag is set in the sched_domain hierarchy.
- * 3. the EM complexity is low enough to keep scheduling overheads low;
- * 4. schedutil is driving the frequency of all CPUs of the rd;
+ * 3. no SMT is detected.
+ * 4. the EM complexity is low enough to keep scheduling overheads low;
+ * 5. schedutil is driving the frequency of all CPUs of the rd;
*
* The complexity of the Energy Model is defined as:
*
@@ -360,6 +361,13 @@ static bool build_perf_domains(const struct cpumask *cpu_map)
goto free;
}

+ /* EAS definitely does *not* handle SMT */
+ if (sched_smt_active()) {
+ pr_warn("rd %*pbl: Disabling EAS, SMT is not supported\n",
+ cpumask_pr_args(cpu_map));
+ goto free;
+ }
+
for_each_cpu(i, cpu_map) {
/* Skip already covered CPUs. */
if (find_pd(pd, i))
--
2.24.0
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