[PATCH v9 3/3] powerpc/sysfs: Add topology/smallcore_thread_siblings[_list]

["Gautham R. Shenoy" <ego@linux.vnet.ibm.com>]

From: "Gautham R. Shenoy" <ego@linux.vnet.ibm.com>

This patch adds two sysfs attributes named smallcore_thread_siblings
and smallcore_thread_siblings_list to the "topology" attribute group
for each CPU device.

The read-only attributes
/sys/device/system/cpu/cpuN/topology/smallcore_thread_siblings and
/sys/device/system/cpu/cpuN/topology/smallcore_thread_siblings_list
will the online siblings of CPU N that share the L1 cache with it on
big-core configurations in cpumask format and cpu-list format
respectively.

Signed-off-by: Gautham R. Shenoy <ego@linux.vnet.ibm.com>
---
 Documentation/ABI/testing/sysfs-devices-system-cpu | 14 ++++
 arch/powerpc/kernel/sysfs.c                        | 91 ++++++++++++++++++++++
 2 files changed, 105 insertions(+)

diff --git a/Documentation/ABI/testing/sysfs-devices-system-cpu b/Documentation/ABI/testing/sysfs-devices-system-cpu
index 7331822..2a80dc2 100644
--- a/Documentation/ABI/testing/sysfs-devices-system-cpu
+++ b/Documentation/ABI/testing/sysfs-devices-system-cpu
@@ -511,3 +511,17 @@ Description:	Control Symetric Multi Threading (SMT)
 
 			 If control status is "forceoff" or "notsupported" writes
 			 are rejected.
+
+What:		/sys/devices/system/cpu/cpu#/topology/smallcore_thread_siblings
+		/sys/devices/system/cpu/cpu#/topology/smallcore_thread_siblings_list
+Date:		Sept 2018
+Contact:	Linux for PowerPC mailing list <linuxppc-dev@ozlabs.org>
+Description: 	CPU topology files that describe the thread siblings of a
+		logical CPU that share the L1-cache with it on POWER9
+		big-core configurations.
+
+		smallcore_thread_siblings: internal kernel map of
+		cpu#'s hardware threads that share L1-cache with cpu#.
+
+		smallcore_thread_siblings_list: human-readable list of
+		cpu#'s hardware threads that share L1-cache with cpu#.
diff --git a/arch/powerpc/kernel/sysfs.c b/arch/powerpc/kernel/sysfs.c
index 755dc98..3049511 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"
@@ -1060,3 +1061,93 @@ static int __init topology_init(void)
 	return 0;
 }
 subsys_initcall(topology_init);
+
+#ifdef CONFIG_SMP
+static ssize_t smallcore_thread_siblings_show(struct device *dev,
+					      struct device_attribute *attr,
+					      char *buf)
+{
+	int cpu = dev->id;
+
+	return cpumap_print_to_pagebuf(false, buf, cpu_smallcore_mask(cpu));
+}
+static DEVICE_ATTR_RO(smallcore_thread_siblings);
+
+static ssize_t
+	smallcore_thread_siblings_list_show(struct device *dev,
+					    struct device_attribute *attr,
+					    char *buf)
+{
+	int cpu = dev->id;
+
+	return cpumap_print_to_pagebuf(true, buf, cpu_smallcore_mask(cpu));
+}
+static DEVICE_ATTR_RO(smallcore_thread_siblings_list);
+
+static struct attribute *smallcore_attrs[] = {
+	&dev_attr_smallcore_thread_siblings.attr,
+	&dev_attr_smallcore_thread_siblings_list.attr,
+	NULL
+};
+
+static const struct attribute_group smallcore_attr_group = {
+	.name = "topology",
+	.attrs = smallcore_attrs
+};
+
+static int smallcore_register_cpu_online(unsigned int cpu)
+{
+	int err;
+	struct device *cpu_dev = get_cpu_device(cpu);
+
+	if (!has_big_cores)
+		return 0;
+
+	err = sysfs_merge_group(&cpu_dev->kobj, &smallcore_attr_group);
+
+	return err;
+}
+
+static int smallcore_unregister_cpu_online(unsigned int cpu)
+{
+	struct device *cpu_dev = get_cpu_device(cpu);
+
+	if (!has_big_cores)
+		return 0;
+
+	sysfs_unmerge_group(&cpu_dev->kobj, &smallcore_attr_group);
+
+	return 0;
+}
+
+/*
+ * NOTE: The smallcore_register_cpu_online
+ *       (resp. smallcore_unregister_cpu_online) callback will merge
+ *       (resp. unmerge) a couple of additional attributes to the
+ *       "topology" attribute group of a CPU device when the CPU comes
+ *       online (resp. goes offline).
+ *
+ *       Hence, the registration of these callbacks must happen after
+ *       topology_sysfs_init() is called so that the topology
+ *       attribute group is created before these additional attributes
+ *       can be merged/unmerged. We cannot register these callbacks in
+ *       topology_init() since this function is called before
+ *       topology_sysfs_init(). Hence we define the following
+ *       late_initcall for this purpose.
+ */
+static int __init smallcore_topology_init(void)
+{
+	int r;
+
+	if (!has_big_cores)
+		return 0;
+
+	r = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN,
+			      "powerpc/topology/smallcore:online",
+			      smallcore_register_cpu_online,
+			      smallcore_unregister_cpu_online);
+	WARN_ON(r < 0);
+	return 0;
+}
+late_initcall(smallcore_topology_init);
+#endif /* CONFIG_SMP */
-- 
1.9.4