Re: [RFC] Add Arm cpu topology definition
From: Daniel Lezcano
Date: Thu Jun 16 2011 - 06:49:15 EST
On 06/16/2011 10:49 AM, Vincent Guittot wrote:
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
ARM_CPU_TOPOLOGY depends on SMP, so the check can be reduced to
depends on 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
depends on SMT && 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;
I am not sure how that deals with the rest of the functions prototype
but wouldn't u16 be more adequate ?
+ 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) {};
AFAIK the convention is to declare static inline noop functions.
static inline void init_cpu_topology(void) { };
static inline void store_cpu_topology(unsigned int 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);
+
}
If the store_cpu_topology function is called once, can it be changed to
a __cpuinit function, declared as a subsys_initcall and removed from here ?
/*
@@ -354,6 +358,8 @@ void __init smp_prepare_cpus(unsigned int max_cpus)
{
unsigned int ncores = num_possible_cpus();
+ init_cpu_topology();
Why do you need to call the init function here ?
On the other architecture I see:
static int __init topology_init(void)
{
...
}
subsys_initcall(topology_init);
Isn't possible to use the same way ? (with the benefit to save two
declarations in the header).
[ ... ]
+
+struct cputopo_arm cpu_topology[NR_CPUS];
IMO, you can define it static here no ?
+
+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;
If the code calls store_cpu_topology but with no effect because it was
already called before, that means it shouldn't be called at all, no ?
IMHO, this test should be removed or at least add a WARN_ONCE.
+
+ 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;
nit : extra space
+ cpu_topo->socket_id = -1;
+ cpumask_clear(&cpu_topo->core_sibling);
+ cpumask_clear(&cpu_topo->thread_sibling);
+ }
+ smp_wmb();
+}
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/