linux-kernel - [PATCH 11/17] pseries/smp: Create soft offline infrastructure for Powerpc shared LPARs.

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Message-ID: <20251204175405.1511340-12-srikar@linux.ibm.com>
Date: Thu,  4 Dec 2025 23:23:59 +0530
From: Srikar Dronamraju <srikar@...ux.ibm.com>
To: linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        Peter Zijlstra <peterz@...radead.org>
Cc: Ben Segall <bsegall@...gle.com>,
        Christophe Leroy <christophe.leroy@...roup.eu>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Ingo Molnar <mingo@...nel.org>, Juri Lelli <juri.lelli@...hat.com>,
        K Prateek Nayak <kprateek.nayak@....com>,
        Madhavan Srinivasan <maddy@...ux.ibm.com>,
        Mel Gorman <mgorman@...e.de>, Michael Ellerman <mpe@...erman.id.au>,
        Nicholas Piggin <npiggin@...il.com>,
        Shrikanth Hegde <sshegde@...ux.ibm.com>,
        Srikar Dronamraju <srikar@...ux.ibm.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Swapnil Sapkal <swapnil.sapkal@....com>,
        Thomas Huth <thuth@...hat.com>,
        Valentin Schneider <vschneid@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        virtualization@...ts.linux.dev, Yicong Yang <yangyicong@...ilicon.com>,
        Ilya Leoshkevich <iii@...ux.ibm.com>
Subject: [PATCH 11/17] pseries/smp: Create soft offline infrastructure for Powerpc shared LPARs.

Create an infrastructure that uses Linux scheduler's new soft
online/offline infrastructure to temporarily enable and disable CPUs.
This utilizes the workqueue mechanism to activate worker functions to
online/offline CPUs as and when requested.

Signed-off-by: Srikar Dronamraju <srikar@...ux.ibm.com>
---
 arch/powerpc/platforms/pseries/smp.c | 39 ++++++++++++++++++++++++++++
 1 file changed, 39 insertions(+)

diff --git a/arch/powerpc/platforms/pseries/smp.c b/arch/powerpc/platforms/pseries/smp.c
index a36153c959d0..ec1af13670f2 100644
--- a/arch/powerpc/platforms/pseries/smp.c
+++ b/arch/powerpc/platforms/pseries/smp.c
@@ -122,6 +122,42 @@ static inline int smp_startup_cpu(unsigned int lcpu)
 	return 1;
 }
 
+#ifdef CONFIG_PPC_SPLPAR
+struct offline_worker {
+	struct work_struct work;
+	int offline;
+	int cpu;
+};
+
+static DEFINE_PER_CPU(struct offline_worker, offline_workers);
+
+static void softoffline_work_fn(struct work_struct *work)
+{
+	struct offline_worker *worker = this_cpu_ptr(&offline_workers);
+
+	set_cpu_softoffline(worker->cpu, worker->offline);
+}
+
+static void softoffline_work_init(void)
+{
+	int cpu;
+
+	if (!is_shared_processor() || is_kvm_guest())
+		return;
+
+	for_each_possible_cpu(cpu) {
+		struct offline_worker *worker = &per_cpu(offline_workers, cpu);
+
+		INIT_WORK(&worker->work, softoffline_work_fn);
+		worker->cpu = cpu;
+	}
+}
+#else
+static void softoffline_work_init(void)
+{
+}
+#endif
+
 static void smp_setup_cpu(int cpu)
 {
 	if (xive_enabled())
@@ -260,6 +296,9 @@ static unsigned int pseries_num_available_cores(void)
 	if (plpar_hcall9(H_GET_PPP, retbuf))
 		return num_present_cpus() / threads_per_core;
 
+	if (!entitled_cores)
+		softoffline_work_init();
+
 	entitled_cores = retbuf[0] / 100;
 	max_virtual_cores = present_cores;
 
-- 
2.43.7