linux-kernel - [tip: sched/core] sched/topology: Don't enable EAS on SMT systems

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Date:   Fri, 06 Mar 2020 14:42:07 -0000
From:   "tip-bot2 for Valentin Schneider" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     Dietmar Eggemann <dietmar.eggemann@....com>,
        Quentin Perret <qperret@...gle.com>,
        Valentin Schneider <valentin.schneider@....com>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>, x86 <x86@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: [tip: sched/core] sched/topology: Don't enable EAS on SMT systems

The following commit has been merged into the sched/core branch of tip:

Commit-ID:     38502ab4bf3c463081bfd53356980a9ec2f32d1d
Gitweb:        https://git.kernel.org/tip/38502ab4bf3c463081bfd53356980a9ec2f32d1d
Author:        Valentin Schneider <valentin.schneider@....com>
AuthorDate:    Thu, 27 Feb 2020 19:14:32 
Committer:     Ingo Molnar <mingo@...nel.org>
CommitterDate: Fri, 06 Mar 2020 12:57:23 +01:00

sched/topology: Don't enable EAS on SMT systems

EAS already requires asymmetric CPU capacities to be enabled, and mixing
this with SMT is an aberration, but better be safe than sorry.

Reviewed-by: Dietmar Eggemann <dietmar.eggemann@....com>
Acked-by: Quentin Perret <qperret@...gle.com>
Signed-off-by: Valentin Schneider <valentin.schneider@....com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Signed-off-by: Ingo Molnar <mingo@...nel.org>
Link: https://lkml.kernel.org/r/20200227191433.31994-2-valentin.schneider@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 0091188..8344757 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))