On 12.07.2014 00:33, Tim Chen wrote:
> This function will help a thread decide if it wants to to do work
> that can be delayed, to accumulate more tasks for more efficient
> batch processing later.
>
> However, if no other tasks are running on the cpu, it can take
> advantgae of the available cpu cycles to complete the tasks
> for immediate processing to minimize delay, otherwise it will yield.
>
> Signed-off-by: Tim Chen <tim.c.chen@xxxxxxxxxxxxxxx>
> ---
> include/linux/sched.h | 1 +
> kernel/sched/core.c | 8 ++++++++
> 2 files changed, 9 insertions(+)
>
> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index 7cb07fd..0884250 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -168,6 +168,7 @@ extern int nr_threads;
> DECLARE_PER_CPU(unsigned long, process_counts);
> extern int nr_processes(void);
> extern unsigned long nr_running(void);
> +extern unsigned long nr_running_cpu(int cpu);
> extern unsigned long nr_iowait(void);
> extern unsigned long nr_iowait_cpu(int cpu);
> extern unsigned long this_cpu_load(void);
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 9cae286..d5bb8e6 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -2283,6 +2283,14 @@ unsigned long nr_running(void)
> return sum;
> }
>
> +unsigned long nr_running_cpu(int cpu)
> +{
> + if (cpumask_test_cpu(cpu, cpu_online_mask))
> + return cpu_rq(cpu)->nr_running;
> + else
> + return 0;
> +}
> +
Offline cpu should have nr_running equal to 0. We park last
enqueued thread (migration_thread) at the end of take_cpu_down().
So, it's enough to return cpu_rq(cpu)->nr_running.
> unsigned long long nr_context_switches(void)
> {
> int i;
>
Thanks,
Kirill
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