From: "Gautham R. Shenoy" <[email protected]>
On POWER platforms where only some groups of threads within a core
share the L2-cache (indicated by the ibm,thread-groups device-tree
property), we currently print the incorrect shared_cpu_map/list for
L2-cache in the sysfs.
This patch reports the correct shared_cpu_map/list on such platforms.
Example:
On a platform with "ibm,thread-groups" set to
00000001 00000002 00000004 00000000
00000002 00000004 00000006 00000001
00000003 00000005 00000007 00000002
00000002 00000004 00000000 00000002
00000004 00000006 00000001 00000003
00000005 00000007
This indicates that threads {0,2,4,6} in the core share the L2-cache
and threads {1,3,5,7} in the core share the L2 cache.
However, without the patch, the shared_cpu_map/list for L2 for CPUs 0,
1 is reported in the sysfs as follows:
/sys/devices/system/cpu/cpu0/cache/index2/shared_cpu_list:0-7
/sys/devices/system/cpu/cpu0/cache/index2/shared_cpu_map:000000,000000ff
/sys/devices/system/cpu/cpu1/cache/index2/shared_cpu_list:0-7
/sys/devices/system/cpu/cpu1/cache/index2/shared_cpu_map:000000,000000ff
With the patch, the shared_cpu_map/list for L2 cache for CPUs 0, 1 is
correctly reported as follows:
/sys/devices/system/cpu/cpu0/cache/index2/shared_cpu_list:0,2,4,6
/sys/devices/system/cpu/cpu0/cache/index2/shared_cpu_map:000000,00000055
/sys/devices/system/cpu/cpu1/cache/index2/shared_cpu_list:1,3,5,7
/sys/devices/system/cpu/cpu1/cache/index2/shared_cpu_map:000000,000000aa
This patch also defines cpu_l2_cache_mask() for !CONFIG_SMP case.
Signed-off-by: Gautham R. Shenoy <[email protected]>
---
arch/powerpc/include/asm/smp.h | 4 ++++
arch/powerpc/kernel/cacheinfo.c | 30 ++++++++++++++++++++----------
2 files changed, 24 insertions(+), 10 deletions(-)
diff --git a/arch/powerpc/include/asm/smp.h b/arch/powerpc/include/asm/smp.h
index 035459c..c4e2d53 100644
--- a/arch/powerpc/include/asm/smp.h
+++ b/arch/powerpc/include/asm/smp.h
@@ -201,6 +201,10 @@ static inline const struct cpumask *cpu_smallcore_mask(int cpu)
return cpumask_of(cpu);
}
+static inline const struct cpumask *cpu_l2_cache_mask(int cpu)
+{
+ return cpumask_of(cpu);
+}
#endif /* CONFIG_SMP */
#ifdef CONFIG_PPC64
diff --git a/arch/powerpc/kernel/cacheinfo.c b/arch/powerpc/kernel/cacheinfo.c
index 65ab9fc..6f903e9a 100644
--- a/arch/powerpc/kernel/cacheinfo.c
+++ b/arch/powerpc/kernel/cacheinfo.c
@@ -655,11 +655,27 @@ static unsigned int index_dir_to_cpu(struct cache_index_dir *index)
* On big-core systems, each core has two groups of CPUs each of which
* has its own L1-cache. The thread-siblings which share l1-cache with
* @cpu can be obtained via cpu_smallcore_mask().
+ *
+ * On some big-core systems, the L2 cache is shared only between some
+ * groups of siblings. This is already parsed and encoded in
+ * cpu_l2_cache_mask().
+ *
+ * TODO: cache_lookup_or_instantiate() needs to be made aware of the
+ * "ibm,thread-groups" property so that cache->shared_cpu_map
+ * reflects the correct siblings on platforms that have this
+ * device-tree property. This helper function is only a stop-gap
+ * solution so that we report the correct siblings to the
+ * userspace via sysfs.
*/
-static const struct cpumask *get_big_core_shared_cpu_map(int cpu, struct cache *cache)
+static const struct cpumask *get_shared_cpu_map(struct cache_index_dir *index, struct cache *cache)
{
- if (cache->level == 1)
- return cpu_smallcore_mask(cpu);
+ if (has_big_cores) {
+ int cpu = index_dir_to_cpu(index);
+ if (cache->level == 1)
+ return cpu_smallcore_mask(cpu);
+ if (cache->level == 2 && thread_group_shares_l2)
+ return cpu_l2_cache_mask(cpu);
+ }
return &cache->shared_cpu_map;
}
@@ -670,17 +686,11 @@ static const struct cpumask *get_big_core_shared_cpu_map(int cpu, struct cache *
struct cache_index_dir *index;
struct cache *cache;
const struct cpumask *mask;
- int cpu;
index = kobj_to_cache_index_dir(k);
cache = index->cache;
- if (has_big_cores) {
- cpu = index_dir_to_cpu(index);
- mask = get_big_core_shared_cpu_map(cpu, cache);
- } else {
- mask = &cache->shared_cpu_map;
- }
+ mask = get_shared_cpu_map(index, cache);
return cpumap_print_to_pagebuf(list, buf, mask);
}
--
1.9.4
* Gautham R. Shenoy <[email protected]> [2020-12-10 16:08:59]:
> From: "Gautham R. Shenoy" <[email protected]>
>
> On POWER platforms where only some groups of threads within a core
> share the L2-cache (indicated by the ibm,thread-groups device-tree
> property), we currently print the incorrect shared_cpu_map/list for
> L2-cache in the sysfs.
>
> This patch reports the correct shared_cpu_map/list on such platforms.
>
> Example:
> On a platform with "ibm,thread-groups" set to
> 00000001 00000002 00000004 00000000
> 00000002 00000004 00000006 00000001
> 00000003 00000005 00000007 00000002
> 00000002 00000004 00000000 00000002
> 00000004 00000006 00000001 00000003
> 00000005 00000007
>
Looks good to me.
Reviewed-by: Srikar Dronamraju <[email protected]>
--
Thanks and Regards
Srikar Dronamraju