linux-kernel - [PATCH v3 6/6] x86/sched: Enable SMT checks for asymmetric packing in load balancing

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Date:   Thu, 13 May 2021 08:49:09 -0700
From:   Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
To:     "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>
Cc:     Dietmar Eggemann <dietmar.eggemann@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
        Len Brown <len.brown@...el.com>,
        Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        Aubrey Li <aubrey.li@...ux.intel.com>,
        "Ravi V. Shankar" <ravi.v.shankar@...el.com>,
        Ricardo Neri <ricardo.neri@...el.com>,
        Quentin Perret <qperret@...gle.com>,
        "Joel Fernandes (Google)" <joel@...lfernandes.org>,
        linux-kernel@...r.kernel.org,
        Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>,
        Aubrey Li <aubrey.li@...el.com>,
        Daniel Bristot de Oliveira <bristot@...hat.com>
Subject: [PATCH v3 6/6] x86/sched: Enable SMT checks for asymmetric packing in load balancing

ITMT relies on asymmetric packing of tasks to ensure CPUs are populated in
priority order. When balancing load, the scheduler compares scheduling
groups in pairs, and compares only the priority of the CPUs of highest
priority in the group. This may result on CPUs with medium priority being
overlooked. A recent change introduced logic to also consider the idle
state of the SMT siblings of the CPU doing the load balance. Enable those
checks for x86 when using ITMT.

Cc: Aubrey Li <aubrey.li@...el.com>
Cc: Ben Segall <bsegall@...gle.com>
Cc: Daniel Bristot de Oliveira <bristot@...hat.com>
Cc: Dietmar Eggemann <dietmar.eggemann@....com>
Cc: Joel Fernandes (Google) <joel@...lfernandes.org>
Cc: Mel Gorman <mgorman@...e.de>
Cc: Quentin Perret <qperret@...gle.com>
Cc: Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>
Cc: Steven Rostedt <rostedt@...dmis.org>
Cc: Tim Chen <tim.c.chen@...ux.intel.com>
Reviewed-by: Len Brown <len.brown@...el.com>
Signed-off-by: Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
---
Changes since v2:
  * Removed arch_sched_asym_prefer_early() as it is no longer needed.

Changes since v1:
  * None
---
 arch/x86/kernel/itmt.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/arch/x86/kernel/itmt.c b/arch/x86/kernel/itmt.c
index 1afbdd1dd777..3c8f0cead574 100644
--- a/arch/x86/kernel/itmt.c
+++ b/arch/x86/kernel/itmt.c
@@ -28,6 +28,8 @@ DEFINE_PER_CPU_READ_MOSTLY(int, sched_core_priority);
 
 /* Boolean to track if system has ITMT capabilities */
 static bool __read_mostly sched_itmt_capable;
+/* Boolean to activate checks on the state of SMT siblings */
+static bool __read_mostly sched_itmt_smt_checks;
 
 /*
  * Boolean to control whether we want to move processes to cpu capable
@@ -124,6 +126,8 @@ int sched_set_itmt_support(void)
 
 	sysctl_sched_itmt_enabled = 1;
 
+	sched_itmt_smt_checks = true;
+
 	x86_topology_update = true;
 	rebuild_sched_domains();
 
@@ -160,6 +164,7 @@ void sched_clear_itmt_support(void)
 	if (sysctl_sched_itmt_enabled) {
 		/* disable sched_itmt if we are no longer ITMT capable */
 		sysctl_sched_itmt_enabled = 0;
+		sched_itmt_smt_checks = false;
 		x86_topology_update = true;
 		rebuild_sched_domains();
 	}
@@ -167,6 +172,11 @@ void sched_clear_itmt_support(void)
 	mutex_unlock(&itmt_update_mutex);
 }
 
+bool arch_asym_check_smt_siblings(void)
+{
+	return sched_itmt_smt_checks;
+}
+
 int arch_asym_cpu_priority(int cpu)
 {
 	return per_cpu(sched_core_priority, cpu);
-- 
2.17.1