linux-kernel - [PATCH v2 7/7] x86/sched/itmt: Consider the idle state of SMT siblings

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Date:   Tue, 22 Nov 2022 12:35:32 -0800
From:   Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
To:     "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>
Cc:     Ricardo Neri <ricardo.neri@...el.com>,
        "Ravi V. Shankar" <ravi.v.shankar@...el.com>,
        Ben Segall <bsegall@...gle.com>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Len Brown <len.brown@...el.com>, Mel Gorman <mgorman@...e.de>,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
        Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        Valentin Schneider <vschneid@...hat.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org,
        Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>,
        "Tim C . Chen" <tim.c.chen@...el.com>
Subject: [PATCH v2 7/7] x86/sched/itmt: Consider the idle state of SMT siblings

Cores with more than one busy SMT sibling need help from fully idle cores,
even if they have lower priority. Return a priority of 0 if any of the SMT
siblings of a CPU are busy. This lets lower-priority idle cores pull tasks
from the CPU.

Only do this if the scheduler cares about the idle state of the siblings.

Cc: Ben Segall <bsegall@...gle.com>
Cc: Daniel Bristot de Oliveira <bristot@...hat.com>
Cc: Dietmar Eggemann <dietmar.eggemann@....com>
Cc: Len Brown <len.brown@...el.com>
Cc: Mel Gorman <mgorman@...e.de>
Cc: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
Cc: Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>
Cc: Steven Rostedt <rostedt@...dmis.org>
Cc: Tim C. Chen <tim.c.chen@...el.com>
Cc: Valentin Schneider <vschneid@...hat.com>
Cc: x86@...nel.org
Cc: linux-kernel@...r.kernel.org
Signed-off-by: Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
---
Changes since v1:
 * Introduced this patch.
---
 arch/x86/kernel/itmt.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/itmt.c b/arch/x86/kernel/itmt.c
index 2be49ce4f94a..cb22944969a1 100644
--- a/arch/x86/kernel/itmt.c
+++ b/arch/x86/kernel/itmt.c
@@ -169,7 +169,10 @@ void sched_clear_itmt_support(void)
 
 int arch_asym_cpu_priority(int cpu, bool check_smt)
 {
-	return per_cpu(sched_core_priority, cpu);
+	if (!check_smt || sched_smt_siblings_idle(cpu))
+		return per_cpu(sched_core_priority, cpu);
+
+	return 0;
 }
 
 /**
-- 
2.25.1