linux-kernel - [PATCH 2/3] powerpc/numa: Populate distance map correctly

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Date:   Thu, 20 May 2021 21:14:26 +0530
From:   Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
To:     Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Rik van Riel <riel@...riel.com>,
        Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Valentin Schneider <valentin.schneider@....com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        linuxppc-dev@...ts.ozlabs.org,
        Nathan Lynch <nathanl@...ux.ibm.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Scott Cheloha <cheloha@...ux.ibm.com>,
        Gautham R Shenoy <ego@...ux.vnet.ibm.com>,
        Geetika Moolchandani <Geetika.Moolchandani1@....com>
Subject: [PATCH 2/3] powerpc/numa: Populate distance map correctly

As per PAPR that defines the OS to hypervisor interface on POWER,
there is no way to calculate the node_distance between 2 nodes, when
either of the nodes are offline. However scheduler needs the distance
map to be populated at boot time. On POWER, this information is
provided within the distance_ref_points_depth array, which needs to be
parsed to extract the potential node distances.

To handle this scenario, lets overload arch_populate_distance_map(),
to provide all the distances that are possible in the current
platform.

Cc: LKML <linux-kernel@...r.kernel.org>
Cc: linuxppc-dev@...ts.ozlabs.org
Cc: Nathan Lynch <nathanl@...ux.ibm.com>
Cc: Michael Ellerman <mpe@...erman.id.au>
Cc: Ingo Molnar <mingo@...nel.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Valentin Schneider <valentin.schneider@....com>
Cc: Scott Cheloha <cheloha@...ux.ibm.com>
Cc: Gautham R Shenoy <ego@...ux.vnet.ibm.com>
Cc: Dietmar Eggemann <dietmar.eggemann@....com>
Cc: Mel Gorman <mgorman@...hsingularity.net>
Cc: Vincent Guittot <vincent.guittot@...aro.org>
Cc: Rik van Riel <riel@...riel.com>
Cc: Geetika Moolchandani <Geetika.Moolchandani1@....com>
Reported-by: Geetika Moolchandani <Geetika.Moolchandani1@....com>
Signed-off-by: Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
---
 arch/powerpc/include/asm/topology.h |  3 +++
 arch/powerpc/mm/numa.c              | 19 +++++++++++++++++++
 2 files changed, 22 insertions(+)

diff --git a/arch/powerpc/include/asm/topology.h b/arch/powerpc/include/asm/topology.h
index e4db64c0e184..d7605d833b8d 100644
--- a/arch/powerpc/include/asm/topology.h
+++ b/arch/powerpc/include/asm/topology.h
@@ -22,6 +22,9 @@ struct drmem_lmb;
 			       cpu_all_mask :				\
 			       node_to_cpumask_map[node])
 
+#define arch_populate_distance_map arch_populate_distance_map
+extern int arch_populate_distance_map(unsigned long *distance_map);
+
 struct pci_bus;
 #ifdef CONFIG_PCI
 extern int pcibus_to_node(struct pci_bus *bus);
diff --git a/arch/powerpc/mm/numa.c b/arch/powerpc/mm/numa.c
index f2bf98bdcea2..9a225b29814a 100644
--- a/arch/powerpc/mm/numa.c
+++ b/arch/powerpc/mm/numa.c
@@ -221,6 +221,25 @@ static void initialize_distance_lookup_table(int nid,
 	}
 }
 
+int arch_populate_distance_map(unsigned long *distance_map)
+{
+	int i;
+	int distance = LOCAL_DISTANCE;
+
+	bitmap_set(distance_map, distance, 1);
+
+	if (!form1_affinity) {
+		bitmap_set(distance_map, REMOTE_DISTANCE, 1);
+		return 0;
+	}
+
+	for (i = 0; i < distance_ref_points_depth; i++) {
+		distance *= 2;
+		bitmap_set(distance_map, distance, 1);
+	}
+	return 0;
+}
+
 /*
  * Returns nid in the range [0..nr_node_ids], or -1 if no useful NUMA
  * info is found.
-- 
2.27.0