linux-kernel - [PATCH v3 04/11] powerpc/smp: Optimize remove_cpu_from

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Date:   Thu,  8 Oct 2020 00:07:53 +0530
From:   Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
To:     Michael Ellerman <mpe@...erman.id.au>
Cc:     linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>,
        Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
        Satheesh Rajendran <sathnaga@...ux.vnet.ibm.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Nicholas Piggin <npiggin@...il.com>,
        Anton Blanchard <anton@...abs.org>,
        "Oliver O'Halloran" <oohall@...il.com>,
        Nathan Lynch <nathanl@...ux.ibm.com>,
        Michael Neuling <mikey@...ling.org>,
        Gautham R Shenoy <ego@...ux.vnet.ibm.com>,
        Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Valentin Schneider <valentin.schneider@....com>,
        Qian Cai <cai@...hat.com>
Subject: [PATCH v3 04/11] powerpc/smp: Optimize remove_cpu_from_masks

While offlining a CPU, system currently iterate through all the CPUs in
the DIE to clear sibling, l2_cache and smallcore maps. However if there
are more cores in a DIE, system can end up spending more time iterating
through CPUs which are completely unrelated.

Optimize this by only iterating through smaller but relevant cpumap.
If shared_cache is set, cpu_l2_cache_map should be relevant else
cpu_sibling_map would be relevant.

Signed-off-by: Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
Tested-by: Satheesh Rajendran <sathnaga@...ux.vnet.ibm.com>
Cc: linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>
Cc: LKML <linux-kernel@...r.kernel.org>
Cc: Michael Ellerman <mpe@...erman.id.au>
Cc: Nicholas Piggin <npiggin@...il.com>
Cc: Anton Blanchard <anton@...abs.org>
Cc: Oliver O'Halloran <oohall@...il.com>
Cc: Nathan Lynch <nathanl@...ux.ibm.com>
Cc: Michael Neuling <mikey@...ling.org>
Cc: Gautham R Shenoy <ego@...ux.vnet.ibm.com>
Cc: Satheesh Rajendran <sathnaga@...ux.vnet.ibm.com>
Cc: Ingo Molnar <mingo@...nel.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Valentin Schneider <valentin.schneider@....com>
Cc: Qian Cai <cai@...hat.com>
---
 arch/powerpc/kernel/smp.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/arch/powerpc/kernel/smp.c b/arch/powerpc/kernel/smp.c
index 8c095fe237b2..2e61a81aad88 100644
--- a/arch/powerpc/kernel/smp.c
+++ b/arch/powerpc/kernel/smp.c
@@ -1263,14 +1263,21 @@ static bool update_mask_by_l2(int cpu, struct cpumask *(*mask_fn)(int))
 #ifdef CONFIG_HOTPLUG_CPU
 static void remove_cpu_from_masks(int cpu)
 {
+	struct cpumask *(*mask_fn)(int) = cpu_sibling_mask;
 	int i;
 
-	for_each_cpu(i, cpu_cpu_mask(cpu)) {
+	if (shared_caches)
+		mask_fn = cpu_l2_cache_mask;
+
+	for_each_cpu(i, mask_fn(cpu)) {
 		set_cpus_unrelated(cpu, i, cpu_l2_cache_mask);
 		set_cpus_unrelated(cpu, i, cpu_sibling_mask);
 		if (has_big_cores)
 			set_cpus_unrelated(cpu, i, cpu_smallcore_mask);
-		if (has_coregroup_support())
+	}
+
+	if (has_coregroup_support()) {
+		for_each_cpu(i, cpu_coregroup_mask(cpu))
 			set_cpus_unrelated(cpu, i, cpu_coregroup_mask);
 	}
 }
-- 
2.17.1