Re: [PATCH 2/2] sched/isolation: Add cpu_is_isolated() API

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On 2/3/23 18:24, Frederic Weisbecker wrote:
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@xxxxxxxx>
Signed-off-by: Frederic Weisbecker <frederic@xxxxxxxxxx>
---
  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 */

CPUs in an isolated cpuset partition is similar to HK_TYPE_DOMAIN CPUs as load balancing is disabled. I can add an API to access the cpumask and add to this API. However, that list is dynamic as it can be changed at run time. Will that be a problem? Or should that be used separately?

Cheers,
Longman




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