On 16 June 2011 23:13, Russell King - ARM Linux <li...@arm.linux.org.uk> wrote: > On Thu, Jun 16, 2011 at 10:49:13AM +0200, Vincent Guittot wrote: >> @@ -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. > > Why place these in the "system type" menu? Wouldn't it be better to > place them along side ARM_CPU_TOPOLOGY, and place that along side > the SMP option too? >
yes, it's a better place >> + >> 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. > > Is there a reason you'd want to disable this? > In fact, I only want to disable sched_mc and sched_smt. I'm going to add default y for ARM_CPU_TOPOLOGY > Please also note that it's "ARM" not "Arm". OK > >> 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)) > > The thing which naggs me about this is that its a static array, and we > know from x86 that static arrays of per-cpu data have various issues > (cache line bouncing, as well as limitations when we end up with large > numbers of CPUs.) > The array is updated sequentially by each processor during boot. Then, it should be used by one cpu when building the sched_domain and when calling the topology sysfs entry. We should not have so many cases where several cpu are accessing simultaneously the cells of the array. > Lastly, x86 seems to do this: > > #define arch_provides_topology_pointers yes > > and the only effect I can find of that define is in drivers/base/topology.c: > > #ifdef arch_provides_topology_pointers > ... > unsigned int cpu = dev->id; \ > return show_cpumap(0, topology_##name(cpu), buf); \ > ... > #else > ... > return show_cpumap(0, topology_##name(dev->id), buf); \ > ... > #endif > > dev->id is type 'u32' which devolves to 'unsigned int' on all supported > arches. So it looks to me like this arch_provides_topology_pointers > define is completely pointless and we just have useless obfuscation for > the hell of it. > > That's not a criticism of your patch, it's pointing out a difference > between x86 and our implementation. > I haven't set arch_provides_topology_pointers because I can't find a difference between setting it or not >> +#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; \ >> + }) > > Please add a definition for CPUID_MPIDR to arch/arm/include/asm/cputype.h > and a read_cpuid_mpidr() function, and use that instead. > ok I can directly use read_cpuid with a definition for CPUID_MPIDR _______________________________________________ linaro-dev mailing list linaro-dev@lists.linaro.org http://lists.linaro.org/mailman/listinfo/linaro-dev