Messages in this thread | | | Date | Tue, 3 Jul 2018 14:16:55 -0300 | From | Murilo Opsfelder Araujo <> | Subject | Re: [v2 PATCH 1/2] powerpc: Detect the presence of big-cores via "ibm, thread-groups" |
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On Tue, Jul 03, 2018 at 04:33:50PM +0530, Gautham R. Shenoy wrote: > From: "Gautham R. Shenoy" <ego@linux.vnet.ibm.com> > > On IBM POWER9, the device tree exposes a property array identifed by > "ibm,thread-groups" which will indicate which groups of threads share a > particular set of resources. > > As of today we only have one form of grouping identifying the group of > threads in the core that share the L1 cache, translation cache and > instruction data flow. > > This patch defines the helper function to parse the contents of > "ibm,thread-groups" and a new structure to contain the parsed output. > > The patch also creates the sysfs file named "small_core_siblings" that > returns the physical ids of the threads in the core that share the L1 > cache, translation cache and instruction data flow. > > Signed-off-by: Gautham R. Shenoy <ego@linux.vnet.ibm.com> > --- > Documentation/ABI/testing/sysfs-devices-system-cpu | 8 ++ > arch/powerpc/include/asm/cputhreads.h | 22 +++++ > arch/powerpc/kernel/setup-common.c | 110 +++++++++++++++++++++ > arch/powerpc/kernel/sysfs.c | 35 +++++++ > 4 files changed, 175 insertions(+) > > diff --git a/Documentation/ABI/testing/sysfs-devices-system-cpu b/Documentation/ABI/testing/sysfs-devices-system-cpu > index 9c5e7732..53a823a 100644 > --- a/Documentation/ABI/testing/sysfs-devices-system-cpu > +++ b/Documentation/ABI/testing/sysfs-devices-system-cpu > @@ -487,3 +487,11 @@ Description: Information about CPU vulnerabilities > "Not affected" CPU is not affected by the vulnerability > "Vulnerable" CPU is affected and no mitigation in effect > "Mitigation: $M" CPU is affected and mitigation $M is in effect > + > +What: /sys/devices/system/cpu/cpu[0-9]+/small_core_sibings
s/small_core_sibings/small_core_siblings
By the way, big_core_siblings was mentioned in the introductory email.
> +Date: 03-Jul-2018 > +KernelVersion: v4.18.0 > +Contact: Gautham R. Shenoy <ego@linux.vnet.ibm.com> > +Description: List of Physical ids of CPUs which share the the L1 cache, > + translation cache and instruction data-flow with this CPU. > +Values: Comma separated list of decimal integers. > diff --git a/arch/powerpc/include/asm/cputhreads.h b/arch/powerpc/include/asm/cputhreads.h > index d71a909..33226d7 100644 > --- a/arch/powerpc/include/asm/cputhreads.h > +++ b/arch/powerpc/include/asm/cputhreads.h > @@ -23,11 +23,13 @@ > extern int threads_per_core; > extern int threads_per_subcore; > extern int threads_shift; > +extern bool has_big_cores; > extern cpumask_t threads_core_mask; > #else > #define threads_per_core 1 > #define threads_per_subcore 1 > #define threads_shift 0 > +#define has_big_cores 0 > #define threads_core_mask (*get_cpu_mask(0)) > #endif > > @@ -69,12 +71,32 @@ static inline cpumask_t cpu_online_cores_map(void) > return cpu_thread_mask_to_cores(cpu_online_mask); > } > > +#define MAX_THREAD_LIST_SIZE 8 > +struct thread_groups { > + unsigned int property; > + unsigned int nr_groups; > + unsigned int threads_per_group; > + unsigned int thread_list[MAX_THREAD_LIST_SIZE]; > +}; > + > #ifdef CONFIG_SMP > int cpu_core_index_of_thread(int cpu); > int cpu_first_thread_of_core(int core); > +int parse_thread_groups(struct device_node *dn, struct thread_groups *tg); > +int get_cpu_thread_group_start(int cpu, struct thread_groups *tg); > #else > static inline int cpu_core_index_of_thread(int cpu) { return cpu; } > static inline int cpu_first_thread_of_core(int core) { return core; } > +static inline int parse_thread_groups(struct device_node *dn, > + struct thread_groups *tg) > +{ > + return -ENODATA; > +} > + > +static inline int get_cpu_thread_group_start(int cpu, struct thread_groups *tg) > +{ > + return -1; > +} > #endif > > static inline int cpu_thread_in_core(int cpu) > diff --git a/arch/powerpc/kernel/setup-common.c b/arch/powerpc/kernel/setup-common.c > index 40b44bb..a78ec66 100644 > --- a/arch/powerpc/kernel/setup-common.c > +++ b/arch/powerpc/kernel/setup-common.c > @@ -402,10 +402,12 @@ void __init check_for_initrd(void) > #ifdef CONFIG_SMP > > int threads_per_core, threads_per_subcore, threads_shift; > +bool has_big_cores = true; > cpumask_t threads_core_mask; > EXPORT_SYMBOL_GPL(threads_per_core); > EXPORT_SYMBOL_GPL(threads_per_subcore); > EXPORT_SYMBOL_GPL(threads_shift); > +EXPORT_SYMBOL_GPL(has_big_cores); > EXPORT_SYMBOL_GPL(threads_core_mask); > > static void __init cpu_init_thread_core_maps(int tpc) > @@ -433,6 +435,108 @@ static void __init cpu_init_thread_core_maps(int tpc) > > u32 *cpu_to_phys_id = NULL; > > +/* > + * parse_thread_groups: Parses the "ibm,thread-groups" device tree > + * property for the CPU device node dn and stores > + * the parsed output in the thread_groups > + * structure tg.
Perhaps document the arguments of this function, as done in the second patch?
> + * > + * ibm,thread-groups[0..N-1] array defines which group of threads in > + * the CPU-device node can be grouped together based on the property. > + * > + * ibm,thread-groups[0] tells us the property based on which the > + * threads are being grouped together. If this value is 1, it implies > + * that the threads in the same group share L1, translation cache. > + * > + * ibm,thread-groups[1] tells us how many such thread groups exist. > + * > + * ibm,thread-groups[2] tells us the number of threads in each such > + * group. > + * > + * ibm,thread-groups[3..N-1] is the list of threads identified by > + * "ibm,ppc-interrupt-server#s" arranged as per their membership in > + * the grouping. > + * > + * Example: If ibm,thread-groups = [1,2,4,5,6,7,8,9,10,11,12] it > + * implies that there are 2 groups of 4 threads each, where each group > + * of threads share L1, translation cache. > + * > + * The "ibm,ppc-interrupt-server#s" of the first group is {5,6,7,8} > + * and the "ibm,ppc-interrupt-server#s" of the second group is {9, 10, > + * 11, 12} structure > + * > + * Returns 0 on success, -EINVAL if the property does not exist, > + * -ENODATA if property does not have a value, and -EOVERFLOW if the > + * property data isn't large enough. > + */ > +int parse_thread_groups(struct device_node *dn, > + struct thread_groups *tg) > +{ > + unsigned int nr_groups, threads_per_group, property; > + int i; > + u32 thread_group_array[3 + MAX_THREAD_LIST_SIZE]; > + u32 *thread_list; > + size_t total_threads; > + int ret; > + > + ret = of_property_read_u32_array(dn, "ibm,thread-groups", > + thread_group_array, 3); > + > + if (ret) > + return ret; > + > + property = thread_group_array[0]; > + nr_groups = thread_group_array[1]; > + threads_per_group = thread_group_array[2]; > + total_threads = nr_groups * threads_per_group; > + > + ret = of_property_read_u32_array(dn, "ibm,thread-groups", > + thread_group_array, > + 3 + total_threads); > + if (ret) > + return ret; > + > + thread_list = &thread_group_array[3]; > + > + for (i = 0 ; i < total_threads; i++) > + tg->thread_list[i] = thread_list[i]; > + > + tg->property = property; > + tg->nr_groups = nr_groups; > + tg->threads_per_group = threads_per_group; > + > + return 0; > +} > + > +/* > + * get_cpu_thread_group_start : Searches the thread group in tg->thread_list > + * that @cpu belongs to.
Same here.
> + * > + * Returns the index to tg->thread_list that points to the the start > + * of the thread_group that @cpu belongs to. > + * > + * Returns -1 if cpu doesn't belong to any of the groups pointed > + * to by tg->thread_list. > + */ > +int get_cpu_thread_group_start(int cpu, struct thread_groups *tg) > +{ > + int hw_cpu_id = get_hard_smp_processor_id(cpu); > + int i, j; > + > + for (i = 0; i < tg->nr_groups; i++) { > + int group_start = i * tg->threads_per_group; > + > + for (j = 0; j < tg->threads_per_group; j++) { > + int idx = group_start + j; > + > + if (tg->thread_list[idx] == hw_cpu_id) > + return group_start; > + } > + } > + > + return -1; > +} > + > /** > * setup_cpu_maps - initialize the following cpu maps: > * cpu_possible_mask > @@ -467,6 +571,7 @@ void __init smp_setup_cpu_maps(void) > const __be32 *intserv; > __be32 cpu_be; > int j, len; > + struct thread_groups tg = {.nr_groups = 0};
We assume has_big_cores = true but here we initialize .nr_groups otherwise. It's kind of contradictory.
What if has_big_cores is assumed false and members of tg are initialized with zeroes?
> > DBG(" * %pOF...\n", dn); > > @@ -505,6 +610,11 @@ void __init smp_setup_cpu_maps(void) > cpu++; > } > > + if (parse_thread_groups(dn, &tg) || > + tg.nr_groups < 1 || tg.property != 1) { > + has_big_cores = false; > + } > +
parse_thread_groups() returns before setting tg.property if property doesn't exist. Are we confident that tg.property won't contain any garbage that could lead to a false positive here? Shouldn't we also initialize .property when declaring tg?
What if this logic is encapsulated in a function? For example:
has_big_cores = dt_has_big_cores(dn, &tg);
> if (cpu >= nr_cpu_ids) { > of_node_put(dn); > break; > diff --git a/arch/powerpc/kernel/sysfs.c b/arch/powerpc/kernel/sysfs.c > index 755dc98..f5717de 100644 > --- a/arch/powerpc/kernel/sysfs.c > +++ b/arch/powerpc/kernel/sysfs.c > @@ -18,6 +18,7 @@ > #include <asm/smp.h> > #include <asm/pmc.h> > #include <asm/firmware.h> > +#include <asm/cputhreads.h> > > #include "cacheinfo.h" > #include "setup.h" > @@ -1025,6 +1026,33 @@ static ssize_t show_physical_id(struct device *dev, > } > static DEVICE_ATTR(physical_id, 0444, show_physical_id, NULL); > > +static ssize_t show_small_core_siblings(struct device *dev, > + struct device_attribute *attr, > + char *buf) > +{ > + struct cpu *cpu = container_of(dev, struct cpu, dev); > + struct device_node *dn = of_get_cpu_node(cpu->dev.id, NULL); > + struct thread_groups tg; > + int i, j; > + ssize_t ret = 0; > + > + if (parse_thread_groups(dn, &tg)) > + return -ENODATA; > + > + i = get_cpu_thread_group_start(cpu->dev.id, &tg); > + > + if (i == -1) > + return -ENODATA; > + > + for (j = 0; j < tg.threads_per_group - 1; j++) > + ret += sprintf(buf + ret, "%d,", tg.thread_list[i + j]); > + > + ret += sprintf(buf + ret, "%d\n", tg.thread_list[i + j]); > + > + return ret; > +} > +static DEVICE_ATTR(small_core_siblings, 0444, show_small_core_siblings, NULL); > + > static int __init topology_init(void) > { > int cpu, r; > @@ -1048,6 +1076,13 @@ static int __init topology_init(void) > register_cpu(c, cpu); > > device_create_file(&c->dev, &dev_attr_physical_id); > + > + if (has_big_cores) { > + const struct device_attribute *attr = > + &dev_attr_small_core_siblings; > + > + device_create_file(&c->dev, attr); > + } > } > } > r = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "powerpc/topology:online", > -- > 1.9.4 >
Cheers Murilo
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