linux-kernel - [RFC PATCH v4 12/17] powerpc: method to initialize ec and vp cores

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Message-ID: <20251119062100.1112520-13-sshegde@linux.ibm.com>
Date: Wed, 19 Nov 2025 11:50:55 +0530
From: Shrikanth Hegde <sshegde@...ux.ibm.com>
To: linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Cc: sshegde@...ux.ibm.com, mingo@...hat.com, peterz@...radead.org,
        juri.lelli@...hat.com, vincent.guittot@...aro.org, tglx@...utronix.de,
        yury.norov@...il.com, maddy@...ux.ibm.com, srikar@...ux.ibm.com,
        gregkh@...uxfoundation.org, pbonzini@...hat.com, seanjc@...gle.com,
        kprateek.nayak@....com, vschneid@...hat.com, iii@...ux.ibm.com,
        huschle@...ux.ibm.com, rostedt@...dmis.org, dietmar.eggemann@....com,
        christophe.leroy@...roup.eu
Subject: [RFC PATCH v4 12/17] powerpc: method to initialize ec and vp cores

During system init, capture the number of EC and VP cores on Shared
Processor LPARs(aka VM). (SPLPAR )

EC - Entitled Cores - Hypervisor(PowerVM) guarantees this many cores
worth of cycles.
VP - Virtual Processor Cores - Total logical cores present in the LPAR.
In SPLPAR's typically there is overcommit of vCPUs. i.e VP > EC.

These values will be used in subsequent patches to calculate number of
cores to use when there is steal time.

Note: DLPAR specific method need to call this again. Yet to be done.

Originally-by: Srikar Dronamraju <srikar@...ux.ibm.com>
Signed-off-by: Shrikanth Hegde <sshegde@...ux.ibm.com>
---
 arch/powerpc/include/asm/smp.h        |  1 +
 arch/powerpc/kernel/smp.c             |  1 +
 arch/powerpc/platforms/pseries/lpar.c | 30 +++++++++++++++++++++++++++
 3 files changed, 32 insertions(+)

diff --git a/arch/powerpc/include/asm/smp.h b/arch/powerpc/include/asm/smp.h
index e41b9ea42122..5a52c6952195 100644
--- a/arch/powerpc/include/asm/smp.h
+++ b/arch/powerpc/include/asm/smp.h
@@ -266,6 +266,7 @@ extern char __secondary_hold;
 extern unsigned int booting_thread_hwid;
 
 extern void __early_start(void);
+void pseries_init_ec_vp_cores(void);
 #endif /* __ASSEMBLER__ */
 
 #endif /* __KERNEL__ */
diff --git a/arch/powerpc/kernel/smp.c b/arch/powerpc/kernel/smp.c
index 68edb66c2964..5a3b52dd625b 100644
--- a/arch/powerpc/kernel/smp.c
+++ b/arch/powerpc/kernel/smp.c
@@ -1732,6 +1732,7 @@ void __init smp_cpus_done(unsigned int max_cpus)
 
 	dump_numa_cpu_topology();
 	build_sched_topology();
+	pseries_init_ec_vp_cores();
 }
 
 /*
diff --git a/arch/powerpc/platforms/pseries/lpar.c b/arch/powerpc/platforms/pseries/lpar.c
index 6a415febc53b..935fced6e127 100644
--- a/arch/powerpc/platforms/pseries/lpar.c
+++ b/arch/powerpc/platforms/pseries/lpar.c
@@ -2029,3 +2029,33 @@ static int __init vpa_debugfs_init(void)
 }
 machine_arch_initcall(pseries, vpa_debugfs_init);
 #endif /* CONFIG_DEBUG_FS */
+
+#ifdef CONFIG_PARAVIRT
+
+static unsigned int virtual_procs __read_mostly;
+static unsigned int entitled_cores __read_mostly;
+static unsigned int available_cores;
+
+void pseries_init_ec_vp_cores(void)
+{
+	unsigned long retbuf[PLPAR_HCALL9_BUFSIZE];
+	int ret;
+
+	if (available_cores && virtual_procs == num_present_cpus() / threads_per_core)
+		return;
+
+	/* Get EC values from hcall */
+	ret = plpar_hcall9(H_GET_PPP, retbuf);
+	WARN_ON_ONCE(ret != 0);
+	if (ret)
+		return;
+
+	entitled_cores = retbuf[0] / 100;
+	virtual_procs = num_present_cpus() / threads_per_core;
+
+	/* Initialize the available cores to all VP initially */
+	available_cores = max(entitled_cores, virtual_procs);
+}
+#else
+void pseries_init_ec_vp_cores(void) { return; }
+#endif
-- 
2.47.3