linux-kernel - [PATCH v4 2/2] nohz: set isolcpus when nohz

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Date:	Thu, 9 Apr 2015 13:00:39 -0400
From:	Chris Metcalf <cmetcalf@...hip.com>
To:	"Peter Zijlstra (Intel)" <peterz@...radead.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	"Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	Ingo Molnar <mingo@...hat.com>, <linux-kernel@...r.kernel.org>
CC:	Chris Metcalf <cmetcalf@...hip.com>
Subject: [PATCH v4 2/2] nohz: set isolcpus when nohz_full is set

nohz_full is only useful with isolcpus also set, since otherwise the
scheduler has to run periodically to try to determine whether to steal
work from other cores.

Accordingly, when booting with nohz_full=xxx on the command line, we
should act as if isolcpus=xxx was also set, and set (or extend) the
isolcpus set to include the nohz_full cpus.

Signed-off-by: Chris Metcalf <cmetcalf@...hip.com>
Acked-by: Mike Galbraith <umgwanakikbuti@...il.com> ["thumbs up!"]
Acked-by: Rik van Riel <riel@...hat.com>
---
v4: update accessor names to make them clearer [PeterZ]

v3: update changelog language to avoid using unclear "implies" [PeterZ]

 kernel/sched/core.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index f0f831e8a345..f8bce1b24cf3 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -6836,6 +6836,7 @@ static int init_sched_domains(const struct cpumask *cpu_map)
 	doms_cur = alloc_sched_domains(ndoms_cur);
 	if (!doms_cur)
 		doms_cur = &fallback_doms;
+	tick_nohz_full_cpumask_or(cpu_isolated_map);
 	cpumask_andnot(doms_cur[0], cpu_map, cpu_isolated_map);
 	err = build_sched_domains(doms_cur[0], NULL);
 	register_sched_domain_sysctl();
-- 
2.1.2

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