[RFC] Add Arm cpu topology definition

[Vincent Guittot]

The affinity between Arm processors is defined in the MPIDR register.
We can identify which processors are in the same cluster,
and which ones have performance interdependency. The cpu topology
 of an Arm platform can be set thanks to this register and this topology
is then used by sched_mc and sched_smt.

Signed-off-by: Vincent Guittot <vincent.guittot@xxxxxxxxxx>
---
 arch/arm/Kconfig                |   26 ++++++++
 arch/arm/include/asm/topology.h |   33 ++++++++++
 arch/arm/kernel/Makefile        |    1 +
 arch/arm/kernel/smp.c           |    6 ++
 arch/arm/kernel/topology.c      |  133 +++++++++++++++++++++++++++++++++++++++
 5 files changed, 199 insertions(+), 0 deletions(-)
 create mode 100644 arch/arm/kernel/topology.c

diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index 9adc278..bacf9af 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -219,6 +219,24 @@ source "kernel/Kconfig.freezer"

 menu "System Type"

+config SCHED_MC
+	bool "Multi-core scheduler support"
+	depends on SMP && ARM_CPU_TOPOLOGY
+	default n
+	help
+	  Multi-core scheduler support improves the CPU scheduler's decision
+	  making when dealing with multi-core CPU chips at a cost of slightly
+	  increased overhead in some places. If unsure say N here.
+
+config SCHED_SMT
+	bool "SMT scheduler support"
+	depends on SMP && ARM_CPU_TOPOLOGY
+	default n
+	help
+	  Improves the CPU scheduler's decision making when dealing with
+	  MultiThreading at a cost of slightly increased overhead in some
+	  places. If unsure say N here.
+
 config MMU
 	bool "MMU-based Paged Memory Management Support"
 	default y
@@ -1062,6 +1080,14 @@ if !MMU
 source "arch/arm/Kconfig-nommu"
 endif

+config ARM_CPU_TOPOLOGY
+	bool "Support cpu topology definition"
+	depends on SMP && CPU_V7
+	help
+	  Support Arm cpu topology definition. The MPIDR register defines
+	  affinity between processors which is used to set the cpu
+	  topology of an Arm System.
+
 config ARM_ERRATA_411920
 	bool "ARM errata: Invalidation of the Instruction Cache operation can fail"
 	depends on CPU_V6 || CPU_V6K
diff --git a/arch/arm/include/asm/topology.h b/arch/arm/include/asm/topology.h
index accbd7c..cb90d0a 100644
--- a/arch/arm/include/asm/topology.h
+++ b/arch/arm/include/asm/topology.h
@@ -1,6 +1,39 @@
 #ifndef _ASM_ARM_TOPOLOGY_H
 #define _ASM_ARM_TOPOLOGY_H

+#ifdef CONFIG_ARM_CPU_TOPOLOGY
+
+#include <linux/cpumask.h>
+
+struct cputopo_arm {
+	int thread_id;
+	int core_id;
+	int socket_id;
+	cpumask_t thread_sibling;
+	cpumask_t core_sibling;
+};
+
+extern struct cputopo_arm cpu_topology[NR_CPUS];
+
+#define topology_physical_package_id(cpu)	(cpu_topology[cpu].socket_id)
+#define topology_core_id(cpu)		(cpu_topology[cpu].core_id)
+#define topology_core_cpumask(cpu)	(&(cpu_topology[cpu].core_sibling))
+#define topology_thread_cpumask(cpu)	(&(cpu_topology[cpu].thread_sibling))
+
+#define mc_capable()	(cpu_topology[0].socket_id != -1)
+#define smt_capable()	(cpu_topology[0].thread_id != -1)
+
+void init_cpu_topology(void);
+void store_cpu_topology(unsigned int cpuid);
+const struct cpumask *cpu_coregroup_mask(unsigned int cpu);
+
+#else
+
+#define init_cpu_topology() {};
+#define store_cpu_topology(cpuid) {};
+
+#endif
+
 #include <asm-generic/topology.h>

 #endif /* _ASM_ARM_TOPOLOGY_H */
diff --git a/arch/arm/kernel/Makefile b/arch/arm/kernel/Makefile
index a5b31af..816a481 100644
--- a/arch/arm/kernel/Makefile
+++ b/arch/arm/kernel/Makefile
@@ -61,6 +61,7 @@ obj-$(CONFIG_IWMMXT)		+= iwmmxt.o
 obj-$(CONFIG_CPU_HAS_PMU)	+= pmu.o
 obj-$(CONFIG_HW_PERF_EVENTS)	+= perf_event.o
 AFLAGS_iwmmxt.o			:= -Wa,-mcpu=iwmmxt
+obj-$(CONFIG_ARM_CPU_TOPOLOGY)  += topology.o

 ifneq ($(CONFIG_ARCH_EBSA110),y)
   obj-y		+= io.o
diff --git a/arch/arm/kernel/smp.c b/arch/arm/kernel/smp.c
index 344e52b..3e8dc3b 100644
--- a/arch/arm/kernel/smp.c
+++ b/arch/arm/kernel/smp.c
@@ -31,6 +31,7 @@
 #include <asm/cacheflush.h>
 #include <asm/cpu.h>
 #include <asm/cputype.h>
+#include <asm/topology.h>
 #include <asm/mmu_context.h>
 #include <asm/pgtable.h>
 #include <asm/pgalloc.h>
@@ -268,6 +269,9 @@ static void __cpuinit smp_store_cpu_info(unsigned int cpuid)
 	struct cpuinfo_arm *cpu_info = &per_cpu(cpu_data, cpuid);

 	cpu_info->loops_per_jiffy = loops_per_jiffy;
+
+	store_cpu_topology(cpuid);
+
 }

 /*
@@ -354,6 +358,8 @@ void __init smp_prepare_cpus(unsigned int max_cpus)
 {
 	unsigned int ncores = num_possible_cpus();

+	init_cpu_topology();
+
 	smp_store_cpu_info(smp_processor_id());

 	/*
diff --git a/arch/arm/kernel/topology.c b/arch/arm/kernel/topology.c
new file mode 100644
index 0000000..d61723c
--- /dev/null
+++ b/arch/arm/kernel/topology.c
@@ -0,0 +1,133 @@
+/*
+ * arch/arm/kernel/topology.c
+ *
+ * Copyright (C) 2011  vincent.guittot@xxxxxxxxxx
+ *
+ * based on arch/sh/kernel/topology.c
+ *
+ * This file is subject to the terms and conditions of the GNU General Public
+ * License.  See the file "COPYING" in the main directory of this archive
+ * for more details.
+ */
+
+#include <linux/cpu.h>
+#include <linux/cpumask.h>
+#include <linux/init.h>
+#include <linux/percpu.h>
+#include <linux/node.h>
+#include <linux/nodemask.h>
+#include <linux/sched.h>
+
+#include <asm/cacheflush.h>
+#include <asm/topology.h>
+
+#define hard_smp_mpidr() \
+	({ \
+		unsigned int cpunum; \
+		__asm__("mrc p15, 0, %0, c0, c0, 5"	\
+			: "=r" (cpunum)); \
+		cpunum; \
+	})
+
+struct cputopo_arm cpu_topology[NR_CPUS];
+
+const struct cpumask *cpu_coregroup_mask(unsigned int cpu)
+{
+	return &(cpu_topology[cpu].core_sibling);
+}
+
+/*
+ * store_cpu_topology is called at boot when only one cpu is running
+ * and with the mutex cpu_hotplug.lock locked, when several cpus have booted,
+ * which prevents simultaneous write access to cpu_topology array
+ */
+void store_cpu_topology(unsigned int cpuid)
+{
+	struct cputopo_arm *cpuid_topo = &(cpu_topology[cpuid]);
+	unsigned int mpidr;
+	unsigned int cpu;
+
+	/* If the cpu topology has been already set, just return */
+	if (cpuid_topo->core_id != -1)
+		return;
+
+	mpidr = hard_smp_mpidr();
+
+	/* create cpu topology mapping */
+	if (mpidr & (0x3 << 30)) {
+		/*
+		 * This is a multiprocessor system
+		 * multiprocessor format & multiprocessor mode field are set
+		 */
+
+		if (mpidr & (0x1 << 24)) {
+			/* core performance interdependency */
+			cpuid_topo->thread_id = (mpidr & 0x3);
+			cpuid_topo->core_id =  ((mpidr >> 8) & 0xF);
+			cpuid_topo->socket_id = ((mpidr >> 16) & 0xFF);
+		} else {
+			/* normal core interdependency */
+			cpuid_topo->thread_id = -1;
+			cpuid_topo->core_id = (mpidr & 0x3);
+			cpuid_topo->socket_id = ((mpidr >> 8) & 0xF);
+		}
+	} else {
+		/*
+		 * This is an uniprocessor system
+		 * we are in multiprocessor format but uniprocessor system
+		 * or in the old uniprocessor format
+		 */
+
+		cpuid_topo->thread_id = -1;
+		cpuid_topo->core_id = 0;
+		cpuid_topo->socket_id = -1;
+	}
+
+	/* update core and thread sibling masks */
+	for_each_possible_cpu(cpu) {
+		struct cputopo_arm *cpu_topo = &(cpu_topology[cpu]);
+
+		if (cpuid_topo->socket_id == cpu_topo->socket_id) {
+			cpumask_set_cpu(cpuid, &cpu_topo->core_sibling);
+			if (cpu != cpuid)
+				cpumask_set_cpu(cpu,
+					&cpuid_topo->core_sibling);
+
+			if (cpuid_topo->core_id == cpu_topo->core_id) {
+				cpumask_set_cpu(cpuid,
+					&cpu_topo->thread_sibling);
+				if (cpu != cpuid)
+					cpumask_set_cpu(cpu,
+						&cpuid_topo->thread_sibling);
+			}
+		}
+	}
+	smp_wmb();
+
+	printk(KERN_INFO "cpu %u : thread %d cpu %d, socket %d, mpidr %x\n",
+		cpuid, cpu_topology[cpuid].thread_id,
+		cpu_topology[cpuid].core_id,
+		cpu_topology[cpuid].socket_id, mpidr);
+
+}
+
+/*
+ * init_cpu_topology is called at boot when only one cpu is running
+ * which prevent simultaneous write access to cpu_topology array
+ */
+void init_cpu_topology(void)
+{
+	unsigned int cpu;
+
+	/* init core mask */
+	for_each_possible_cpu(cpu) {
+		struct cputopo_arm *cpu_topo = &(cpu_topology[cpu]);
+
+		cpu_topo->thread_id = -1;
+		cpu_topo->core_id =  -1;
+		cpu_topo->socket_id = -1;
+		cpumask_clear(&cpu_topo->core_sibling);
+		cpumask_clear(&cpu_topo->thread_sibling);
+	}
+	smp_wmb();
+}
-- 
1.7.4.1
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