Re: [PATCH RESEND] nohz: Affining unpinned timers

From: Preeti U Murthy
Date: Wed Jun 24 2015 - 03:17:54 EST


On 06/23/2015 02:01 PM, Vatika Harlalka wrote:
> The problem addressed in this patch is about affining unpinned timers.
> Adaptive or Full Dynticks CPUs should not be disturbed by unnecessary
> jitter due to firing of such timers on them.
> This patch will affine timers to online CPUs which are not Full Dynticks
> in FULL_NOHZ configured systems. It will not bring about functional
> changes if NOHZ_FULL is not configured, because is_housekeeping_cpu()
> always returns true in CONFIG_NO_HZ_FULL=n.
>
> Signed-off by: Vatika Harlalka <vatikaharlalka@xxxxxxxxx>
> ---

Reviewed-by: Preeti U Murthy <preeti@xxxxxxxxxxxxxxxxxx>

> Changes: Patch sent to the right recipients.
>
> include/linux/tick.h | 9 ++++++++-
> kernel/sched/core.c | 9 +++++++--
> 2 files changed, 15 insertions(+), 3 deletions(-)
>
> diff --git a/include/linux/tick.h b/include/linux/tick.h
> index f8492da5..145bcba 100644
> --- a/include/linux/tick.h
> +++ b/include/linux/tick.h
> @@ -133,13 +133,20 @@ static inline bool tick_nohz_full_cpu(int cpu)
>
> return cpumask_test_cpu(cpu, tick_nohz_full_mask);
> }
> -
> +static inline int housekeeping_any_cpu(void)
> +{
> + return cpumask_any_and(housekeeping_mask, cpu_online_mask);
> +}
> extern void __tick_nohz_full_check(void);
> extern void tick_nohz_full_kick(void);
> extern void tick_nohz_full_kick_cpu(int cpu);
> extern void tick_nohz_full_kick_all(void);
> extern void __tick_nohz_task_switch(struct task_struct *tsk);
> #else
> +static inline int housekeeping_any_cpu(void)
> +{
> + return smp_processor_id();
> +}
> static inline bool tick_nohz_full_enabled(void) { return false; }
> static inline bool tick_nohz_full_cpu(int cpu) { return false; }
> static inline void __tick_nohz_full_check(void) { }
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 57bd333..acee856 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -599,18 +599,23 @@ int get_nohz_timer_target(int pinned)
> int i;
> struct sched_domain *sd;
>
> - if (pinned || !get_sysctl_timer_migration() || !idle_cpu(cpu))
> + if (pinned || !get_sysctl_timer_migration() ||
> + (!idle_cpu(cpu) && is_housekeeping_cpu(cpu)))
> return cpu;
>
> rcu_read_lock();
> for_each_domain(cpu, sd) {
> for_each_cpu(i, sched_domain_span(sd)) {
> - if (!idle_cpu(i)) {
> + if (!idle_cpu(i) && is_housekeeping_cpu(cpu)) {
> cpu = i;
> goto unlock;
> }
> }
> }
> +
> + if (!is_housekeeping_cpu(cpu))
> + cpu = housekeeping_any_cpu();
> +
> unlock:
> rcu_read_unlock();
> return cpu;
>

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