linux-kernel - [PATCH v2 10/10] powerpc/smp: Implement cpu_to_coregroup

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Message-Id: <20200721113814.32284-11-srikar@linux.vnet.ibm.com>
Date:   Tue, 21 Jul 2020 17:08:14 +0530
From:   Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
To:     Michael Ellerman <michaele@....ibm.com>
Cc:     Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Valentin Schneider <valentin.schneider@....com>,
        Nick Piggin <npiggin@....ibm.com>,
        Oliver OHalloran <oliveroh@....ibm.com>,
        Nathan Lynch <nathanl@...ux.ibm.com>,
        Michael Neuling <mikey@...ux.ibm.com>,
        Anton Blanchard <anton@....ibm.com>,
        Gautham R Shenoy <ego@...ux.vnet.ibm.com>,
        Vaidyanathan Srinivasan <svaidy@...ux.ibm.com>,
        Jordan Niethe <jniethe5@...il.com>
Subject: [PATCH v2 10/10] powerpc/smp: Implement cpu_to_coregroup_id

Lookup the coregroup id from the associativity array.

If unable to detect the coregroup id, fallback on the core id.
This way, ensure sched_domain degenerates and an extra sched domain is
not created.

Ideally this function should have been implemented in
arch/powerpc/kernel/smp.c. However if its implemented in mm/numa.c, we
don't need to find the primary domain again.

If the device-tree mentions more than one coregroup, then kernel
implements only the last or the smallest coregroup, which currently
corresponds to the penultimate domain in the device-tree.

Cc: linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>
Cc: LKML <linux-kernel@...r.kernel.org>
Cc: Michael Ellerman <michaele@....ibm.com>
Cc: Ingo Molnar <mingo@...nel.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Valentin Schneider <valentin.schneider@....com>
Cc: Nick Piggin <npiggin@....ibm.com>
Cc: Oliver OHalloran <oliveroh@....ibm.com>
Cc: Nathan Lynch <nathanl@...ux.ibm.com>
Cc: Michael Neuling <mikey@...ux.ibm.com>
Cc: Anton Blanchard <anton@....ibm.com>
Cc: Gautham R Shenoy <ego@...ux.vnet.ibm.com>
Cc: Vaidyanathan Srinivasan <svaidy@...ux.ibm.com>
Cc: Jordan Niethe <jniethe5@...il.com>
Signed-off-by: Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
---
Changelog v1 -> v2:
powerpc/smp: Implement cpu_to_coregroup_id
	Move coregroup_enabled before getting associativity (Gautham)

 arch/powerpc/mm/numa.c | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/arch/powerpc/mm/numa.c b/arch/powerpc/mm/numa.c
index ef8aa580da21..ae57b68beaee 100644
--- a/arch/powerpc/mm/numa.c
+++ b/arch/powerpc/mm/numa.c
@@ -1218,6 +1218,26 @@ int find_and_online_cpu_nid(int cpu)
 
 int cpu_to_coregroup_id(int cpu)
 {
+	__be32 associativity[VPHN_ASSOC_BUFSIZE] = {0};
+	int index;
+
+	if (cpu < 0 || cpu > nr_cpu_ids)
+		return -1;
+
+	if (!coregroup_enabled)
+		goto out;
+
+	if (!firmware_has_feature(FW_FEATURE_VPHN))
+		goto out;
+
+	if (vphn_get_associativity(cpu, associativity))
+		goto out;
+
+	index = of_read_number(associativity, 1);
+	if (index > min_common_depth + 1)
+		return of_read_number(&associativity[index - 1], 1);
+
+out:
 	return cpu_to_core_id(cpu);
 }
 
-- 
2.17.1