linux-kernel - [PATCH 3/3] powerpc/cacheinfo: Print correct cache-sibling map/list for L2 cache

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Date:   Fri,  4 Dec 2020 10:18:47 +0530
From:   "Gautham R. Shenoy" <ego@...ux.vnet.ibm.com>
To:     Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
        Anton Blanchard <anton@...abs.org>,
        Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Michael Neuling <mikey@...ling.org>,
        Nicholas Piggin <npiggin@...il.com>,
        Nathan Lynch <nathanl@...ux.ibm.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Valentin Schneider <valentin.schneider@....com>
Cc:     linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
        "Gautham R. Shenoy" <ego@...ux.vnet.ibm.com>
Subject: [PATCH 3/3] powerpc/cacheinfo: Print correct cache-sibling map/list for L2 cache

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

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

Signed-off-by: Gautham R. Shenoy <ego@...ux.vnet.ibm.com>
---
 arch/powerpc/kernel/cacheinfo.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/arch/powerpc/kernel/cacheinfo.c b/arch/powerpc/kernel/cacheinfo.c
index 65ab9fc..1cc8f37 100644
--- a/arch/powerpc/kernel/cacheinfo.c
+++ b/arch/powerpc/kernel/cacheinfo.c
@@ -651,15 +651,22 @@ static unsigned int index_dir_to_cpu(struct cache_index_dir *index)
 	return dev->id;
 }
 
+extern bool thread_group_shares_l2;
 /*
  * 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().
  */
 static const struct cpumask *get_big_core_shared_cpu_map(int cpu, struct cache *cache)
 {
 	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;
 }
-- 
1.9.4