Re: [PATCH-cgroup v2] cgroup/cpuset: Include isolated cpuset CPUs in cpu_is_isolated() check

[Bagas Sanjaya <bagasdotme@gmail.com>]

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On Tue, Dec 05, 2023 at 05:21:14PM -0500, Waiman Long wrote:
> Currently, the cpu_is_isolated() function checks only the statically
> isolated CPUs specified via the "isolcpus" and "nohz_full" kernel
> command line options. This function is used by vmstat and memcg to
> reduce interference with isolated CPUs by not doing stat flushing
> or scheduling works on those CPUs.
> 
> Workloads running on isolated CPUs within isolated cpuset
> partitions should receive the same treatment to reduce unnecessary
> interference. This patch introduces a new cpuset_cpu_is_isolated()
> function to be called by cpu_is_isolated() so that the set of dynamically
> created cpuset isolated CPUs will be included in the check.
> 
> Assuming that testing a bit in a cpumask is atomic, no synchronization
> primitive is currently used to synchronize access to the cpuset's
> isolated_cpus mask.
> 
> Signed-off-by: Waiman Long <longman@redhat.com>
> ---
>  include/linux/cpuset.h          |  6 ++++++
>  include/linux/sched/isolation.h |  4 +++-
>  kernel/cgroup/cpuset.c          | 11 +++++++++++
>  3 files changed, 20 insertions(+), 1 deletion(-)
> 
> diff --git a/include/linux/cpuset.h b/include/linux/cpuset.h
> index d629094fac6e..875d12598bd2 100644
> --- a/include/linux/cpuset.h
> +++ b/include/linux/cpuset.h
> @@ -77,6 +77,7 @@ extern void cpuset_lock(void);
>  extern void cpuset_unlock(void);
>  extern void cpuset_cpus_allowed(struct task_struct *p, struct cpumask *mask);
>  extern bool cpuset_cpus_allowed_fallback(struct task_struct *p);
> +extern bool cpuset_cpu_is_isolated(int cpu);
>  extern nodemask_t cpuset_mems_allowed(struct task_struct *p);
>  #define cpuset_current_mems_allowed (current->mems_allowed)
>  void cpuset_init_current_mems_allowed(void);
> @@ -207,6 +208,11 @@ static inline bool cpuset_cpus_allowed_fallback(struct task_struct *p)
>  	return false;
>  }
>  
> +static inline bool cpuset_cpu_is_isolated(int cpu)
> +{
> +	return false;
> +}
> +
>  static inline nodemask_t cpuset_mems_allowed(struct task_struct *p)
>  {
>  	return node_possible_map;
> diff --git a/include/linux/sched/isolation.h b/include/linux/sched/isolation.h
> index fe1a46f30d24..2b461129d1fa 100644
> --- a/include/linux/sched/isolation.h
> +++ b/include/linux/sched/isolation.h
> @@ -2,6 +2,7 @@
>  #define _LINUX_SCHED_ISOLATION_H
>  
>  #include <linux/cpumask.h>
> +#include <linux/cpuset.h>
>  #include <linux/init.h>
>  #include <linux/tick.h>
>  
> @@ -67,7 +68,8 @@ static inline bool housekeeping_cpu(int cpu, enum hk_type type)
>  static inline bool cpu_is_isolated(int cpu)
>  {
>  	return !housekeeping_test_cpu(cpu, HK_TYPE_DOMAIN) ||
> -		 !housekeeping_test_cpu(cpu, HK_TYPE_TICK);
> +	       !housekeeping_test_cpu(cpu, HK_TYPE_TICK) ||
> +	       cpuset_cpu_is_isolated(cpu);
>  }
>  
>  #endif /* _LINUX_SCHED_ISOLATION_H */
> diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
> index 2a16df86c55c..dfbb16aca9f4 100644
> --- a/kernel/cgroup/cpuset.c
> +++ b/kernel/cgroup/cpuset.c
> @@ -1518,6 +1518,17 @@ static void update_unbound_workqueue_cpumask(bool isolcpus_updated)
>  	WARN_ON_ONCE(ret < 0);
>  }
>  
> +/**
> + * cpuset_cpu_is_isolated - Check if the given CPU is isolated
> + * @cpu: the CPU number to be checked
> + * Return: true if CPU is used in an isolated partition, false otherwise
> + */
> +bool cpuset_cpu_is_isolated(int cpu)
> +{
> +	return cpumask_test_cpu(cpu, isolated_cpus);
> +}
> +EXPORT_SYMBOL_GPL(cpuset_cpu_is_isolated);
> +
>  /*
>   * compute_effective_exclusive_cpumask - compute effective exclusive CPUs
>   * @cs: cpuset


No regressions when booting the kernel with this patch applied.

Tested-by: Bagas Sanjaya <bagasdotme@gmail.com>

-- 
An old man doll... just what I always wanted! - Clara

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