Re: [PATCH 19/32] nohz/cpuset: Restart tick when nohz flag is cleared on cpuset

Peter Zijlstra
2011-08-29T16:02:22Z

On Mon, 2011-08-15 at 17:52 +0200, Frederic Weisbecker wrote:
> +++ b/kernel/cpuset.c
> @@ -1199,6 +1199,14 @@ static void cpuset_change_flag(struct task_struct *tsk,
>
> DEFINE_PER_CPU(int, cpu_adaptive_nohz_ref);
>
> +static void cpu_exit_nohz(int cpu)
> +{
> + preempt_disable();
> + smp_call_function_single(cpu, cpuset_exit_nohz_interrupt,
> + NULL, true);
> + preempt_enable();
> +}
> +
> static void update_nohz_cpus(struct cpuset *old_cs, struct cpuset *cs)
> {
> int cpu;
> @@ -1212,6 +1220,19 @@ static void update_nohz_cpus(struct cpuset *old_cs, struct cpuset *cs)
> per_cpu(cpu_adaptive_nohz_ref, cpu) += 1;
> else
> per_cpu(cpu_adaptive_nohz_ref, cpu) -= 1;
> +
> + val = per_cpu(cpu_adaptive_nohz_ref, cpu);
> +
> + if (!val) {
> + /*
> + * The update to cpu_adaptive_nohz_ref must be
> + * visible right away. So that once we restart the tick
> + * from the IPI, it won't be stopped again due to cache
> + * update lag.
> + */
> + smp_mb();
> + cpu_exit_nohz(cpu);
> + }
> }
> }
> #else
> diff --git a/kernel/sched.c b/kernel/sched.c
> index 78ea0a5..75378be 100644
> --- a/kernel/sched.c
> +++ b/kernel/sched.c
> @@ -2513,6 +2513,14 @@ void cpuset_update_nohz(void)
> cpuset_nohz_restart_tick();
> }
>
> +void cpuset_exit_nohz_interrupt(void *unused)
> +{
> + if (!tick_nohz_adaptive_mode())
> + return;
> +
> + cpuset_nohz_restart_tick();
> +}

You do this just to annoy me, right? Why doesn't it live in cpuset.c
where you use it?