From:   Frederic Weisbecker <frederic@kernel.org>
To:     LKML <linux-kernel@vger.kernel.org>
Cc:     Frederic Weisbecker <frederic@kernel.org>,
        Roman Gushchin <roman.gushchin@linux.dev>,
        Michal Hocko <mhocko@suse.com>,
        Marcelo Tosatti <mtosatti@redhat.com>,
        Leonardo <leobras@redhat.com>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Shakeel Butt <shakeelb@google.com>,
        Muchun Song <muchun.song@linux.dev>,
        Andrew Morton <akpm@linux-foundation.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Thomas Gleixner <tglx@linutronix.de>, cgroups@vger.kernel.org,
        linux-mm@kvack.org
Subject: [PATCH 2/2] sched/isolation: Add cpu_is_isolated() API
Date:   Sat,  4 Feb 2023 00:24:09 +0100
Message-Id: <20230203232409.163847-3-frederic@kernel.org>
In-Reply-To: <20230203232409.163847-1-frederic@kernel.org>
References: <20230203232409.163847-1-frederic@kernel.org>
MIME-Version: 1.0
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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@suse.com>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
---
 include/linux/sched/isolation.h | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/include/linux/sched/isolation.h b/include/linux/sched/isolation.h
index b645cc81fe01..088672f08469 100644
--- a/include/linux/sched/isolation.h
+++ b/include/linux/sched/isolation.h
@@ -53,4 +53,10 @@ 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_KERNEL_NOISE);
+}
+
 #endif /* _LINUX_SCHED_ISOLATION_H */
-- 
2.34.1