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From:   Srikar Dronamraju <srikar@linux.vnet.ibm.com>
To:     Michael Ellerman <mpe@ellerman.id.au>,
        Nicholas Piggin <npiggin@gmail.com>,
        Christophe Leroy <christophe.leroy@csgroup.eu>
Cc:     linuxppc-dev <linuxppc-dev@lists.ozlabs.org>,
        Srikar Dronamraju <srikar@linux.vnet.ibm.com>,
        Josh Poimboeuf <jpoimboe@kernel.org>,
        linux-kernel@vger.kernel.org, Mark Rutland <mark.rutland@arm.com>,
        "Paul E. McKenney" <paulmck@kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Rohan McLure <rmclure@linux.ibm.com>,
        Valentin Schneider <vschneid@redhat.com>,
        Vincent Guittot <vincent.guittot@linaro.org>,
        Aneesh <aneesh.kumar@kernel.org>,
        "ndesaulniers@google.com" <ndesaulniers@google.com>
Subject: [PATCH v5 4/5] powerpc/smp: Avoid asym packing within thread_group of a core
Date:   Thu, 14 Dec 2023 23:37:14 +0530
Message-ID: <20231214180720.310852-5-srikar@linux.vnet.ibm.com>
In-Reply-To: <20231214180720.310852-1-srikar@linux.vnet.ibm.com>
References: <20231214180720.310852-1-srikar@linux.vnet.ibm.com>
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PowerVM Hypervisor will schedule at a core granularity. However each
core can have more than one thread_groups. For better utilization in
case of a shared processor, its preferable for the scheduler to pack to
the lowest core. However there is no benefit of moving a thread between
two thread groups of the same core.

Signed-off-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
---
 arch/powerpc/kernel/smp.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/arch/powerpc/kernel/smp.c b/arch/powerpc/kernel/smp.c
index aea149627209..9d8bb9a084bd 100644
--- a/arch/powerpc/kernel/smp.c
+++ b/arch/powerpc/kernel/smp.c
@@ -1763,6 +1763,19 @@ void __init smp_cpus_done(unsigned int max_cpus)
 	set_sched_topology(powerpc_topology);
 }
 
+/*
+ * For asym packing, by default lower numbered CPU has higher priority.
+ * On shared processors, pack to lower numbered core. However avoid moving
+ * between thread_groups within the same core.
+ */
+int arch_asym_cpu_priority(int cpu)
+{
+	if (static_branch_unlikely(&splpar_asym_pack))
+		return -cpu / threads_per_core;
+
+	return -cpu;
+}
+
 #ifdef CONFIG_HOTPLUG_CPU
 int __cpu_disable(void)
 {
-- 
2.35.3