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SubjectRe: [PATCH v2 1/4] sched/isolation: API to get housekeeping online CPUs
On Wed, Sep 23, 2020 at 02:11:23PM -0400, Nitesh Narayan Lal wrote:
> Introduce a new API hk_num_online_cpus(), that can be used to
> retrieve the number of online housekeeping CPUs that are meant to handle
> managed IRQ jobs.
>
> This API is introduced for the drivers that were previously relying only
> on num_online_cpus() to determine the number of MSIX vectors to create.
> In an RT environment with large isolated but fewer housekeeping CPUs this
> was leading to a situation where an attempt to move all of the vectors
> corresponding to isolated CPUs to housekeeping CPUs were failing due to
> per CPU vector limit.
>
> Signed-off-by: Nitesh Narayan Lal <nitesh@redhat.com>
> ---
> include/linux/sched/isolation.h | 13 +++++++++++++
> 1 file changed, 13 insertions(+)
>
> diff --git a/include/linux/sched/isolation.h b/include/linux/sched/isolation.h
> index cc9f393e2a70..2e96b626e02e 100644
> --- a/include/linux/sched/isolation.h
> +++ b/include/linux/sched/isolation.h
> @@ -57,4 +57,17 @@ static inline bool housekeeping_cpu(int cpu, enum hk_flags flags)
> return true;
> }
>
> +static inline unsigned int hk_num_online_cpus(void)
> +{
> +#ifdef CONFIG_CPU_ISOLATION
> + const struct cpumask *hk_mask;
> +
> + if (static_branch_unlikely(&housekeeping_overridden)) {
> + hk_mask = housekeeping_cpumask(HK_FLAG_MANAGED_IRQ);

HK_FLAG_MANAGED_IRQ should be pass as an argument to the function:

housekeeping_num_online_cpus(HK_FLAG_MANAGED_IRQ) because it's
completely arbitrary otherwise.

> + return cpumask_weight(hk_mask);
> + }
> +#endif
> + return cpumask_weight(cpu_online_mask);
> +}
> +
> #endif /* _LINUX_SCHED_ISOLATION_H */
> --
> 2.18.2
>

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