linux-kernel - [PATCH 1/2] sched/isolation: Add cpu_is

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Message-Id: <20230317134448.11082-2-mhocko@kernel.org>
Date:   Fri, 17 Mar 2023 14:44:47 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Andrew Morton <akpm@...ux-foundation.org>,
        Leonardo Bras <leobras@...hat.com>
Cc:     Frederic Weisbecker <fweisbecker@...e.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Marcelo Tosatti <mtosatti@...hat.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Roman Gushchin <roman.gushchin@...ux.dev>,
        Shakeel Butt <shakeelb@...gle.com>,
        Muchun Song <muchun.song@...ux.dev>,
        LKML <linux-kernel@...r.kernel.org>, <linux-mm@...ck.org>,
        Frederic Weisbecker <frederic@...nel.org>,
        Michal Hocko <mhocko@...e.com>
Subject: [PATCH 1/2] sched/isolation: Add cpu_is_isolated() API

From: Frederic Weisbecker <frederic@...nel.org>

Provide this new API to check if a CPU has been isolated either through
isolcpus= or nohz_full= kernel parameter.

It aims at avoiding kernel load deemed to be safely spared on CPUs
running sensitive workload that can't bear any disturbance, such as
pcp cache draining.

Suggested-by: Michal Hocko <mhocko@...e.com>
Signed-off-by: Frederic Weisbecker <frederic@...nel.org>
Signed-off-by: Michal Hocko <mhocko@...e.com>
---
 include/linux/sched/isolation.h | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/include/linux/sched/isolation.h b/include/linux/sched/isolation.h
index 8c15abd67aed..fe1a46f30d24 100644
--- a/include/linux/sched/isolation.h
+++ b/include/linux/sched/isolation.h
@@ -46,6 +46,12 @@ static inline bool housekeeping_enabled(enum hk_type type)
 
 static inline void housekeeping_affine(struct task_struct *t,
 				       enum hk_type type) { }
+
+static inline bool housekeeping_test_cpu(int cpu, enum hk_type type)
+{
+	return true;
+}
+
 static inline void housekeeping_init(void) { }
 #endif /* CONFIG_CPU_ISOLATION */
 
@@ -58,4 +64,10 @@ static inline bool housekeeping_cpu(int cpu, enum hk_type type)
 	return true;
 }
 
+static inline bool cpu_is_isolated(int cpu)
+{
+	return !housekeeping_test_cpu(cpu, HK_TYPE_DOMAIN) ||
+		 !housekeeping_test_cpu(cpu, HK_TYPE_TICK);
+}
+
 #endif /* _LINUX_SCHED_ISOLATION_H */
-- 
2.30.2