On 05/03/2012 08:25 PM, Gilad Ben-Yossef wrote:
> Introduce schedule_on_each_cpu_mask function to schedule a work
> item on each online CPU which is included in the mask provided.
>
> Then re-implement schedule_on_each_cpu on top of the new function.
>
> This function should be prefered to schedule_on_each_cpu in
> any case where some of the CPUs, especially on a big multi-core
> system, might not have actual work to perform in order to save
> needless wakeups and schedules.
>
> Signed-off-by: Gilad Ben-Yossef <gilad@xxxxxxxxxxxxx>
> /**
> - * schedule_on_each_cpu - execute a function synchronously on each online CPU
> + * schedule_on_each_cpu_mask - execute a function synchronously on each
> + * online CPU which is specified in the supplied cpumask
> * @func: the function to call
> + * @mask: the cpu mask
> *
> - * schedule_on_each_cpu() executes @func on each online CPU using the
> - * system workqueue and blocks until all CPUs have completed.
> - * schedule_on_each_cpu() is very slow.
> + * schedule_on_each_cpu_mask() executes @func on each online CPU which
> + * is part of the @mask using the * system workqueue and blocks until
^^^
stray character?
> + * all CPUs have completed
> + * schedule_on_each_cpu_mask() is very slow.
> *
> * RETURNS:
> * 0 on success, -errno on failure.
> */
> -int schedule_on_each_cpu(work_func_t func)
> +int schedule_on_each_cpu_mask(work_func_t func, const struct cpumask *mask)
> {
> int cpu;
> struct work_struct __percpu *works;
>
> works = alloc_percpu(struct work_struct);
> - if (!works)
> + if (unlikely(!works))
> return -ENOMEM;
>
> get_online_cpus();
>
> - for_each_online_cpu(cpu) {
> + for_each_cpu_and(cpu, mask, cpu_online_mask) {
> struct work_struct *work = per_cpu_ptr(works, cpu);
>
> INIT_WORK(work, func);
> schedule_work_on(cpu, work);
> }
>
> - for_each_online_cpu(cpu)
> + for_each_cpu_and(cpu, mask, cpu_online_mask)
> flush_work(per_cpu_ptr(works, cpu));
>
Given that cpu hotplug is not a frequent operation, I think mask will be
a subset of cpu_online_mask most of the time (also, one example is from
schedule_on_each_cpu_cond() introduced in 3/6, which is already under
get/put_online_cpus(). So can we optimize something (the 'and' operations
perhaps) based on that?
May be something by using:
if (likely(cpumask_subset(mask, cpu_online_mask))
> put_online_cpus();
> free_percpu(works);
> +
> return 0;
> }
>
Regards,
Srivatsa S. Bhat
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