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Message-ID: <BANLkTikgodT0ze7hPM7Lk3Lhi8zPALNm0A@mail.gmail.com>
Date: Thu, 16 Jun 2011 14:10:34 +0200
From: Vincent Guittot <vincent.guittot@...aro.org>
To: Amit Kachhap <amit.kachhap@...aro.org>
Cc: linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
linaro-dev@...ts.linaro.org
Subject: Re: [RFC] Add Arm cpu topology definition
On 16 June 2011 13:55, Amit Kachhap <amit.kachhap@...aro.org> wrote:
> I have some doubts about the bit fields of the MPIDR register.
> Comments added below.
> On 16 June 2011 14:19, Vincent Guittot <vincent.guittot@...aro.org> 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@...aro.org>
>> ---
>> 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@...aro.org
>> + *
>> + * 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)) {
>
> I checked the A9 reference manual. It says bit 30 if 0 denotes that processor is
> part of multiprocessor system.
>
You're right, i'm going to update my test
>
>> + /*
>> + * 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
>>
>> _______________________________________________
>> linaro-dev mailing list
>> linaro-dev@...ts.linaro.org
>> http://lists.linaro.org/mailman/listinfo/linaro-dev
>>
>
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