linux-kernel - Re: [PATCH v1 3/6] workqueue: introduce schedule_on_each_cpu

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Date:	Fri, 04 May 2012 10:21:17 +0530
From:	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>
To:	Gilad Ben-Yossef <gilad@...yossef.com>
CC:	linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
	Tejun Heo <tj@...nel.org>, John Stultz <johnstul@...ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Mel Gorman <mel@....ul.ie>, Mike Frysinger <vapier@...too.org>,
	David Rientjes <rientjes@...gle.com>,
	Hugh Dickins <hughd@...gle.com>,
	Minchan Kim <minchan.kim@...il.com>,
	Konstantin Khlebnikov <khlebnikov@...nvz.org>,
	Christoph Lameter <cl@...ux.com>,
	Chris Metcalf <cmetcalf@...era.com>,
	Hakan Akkan <hakanakkan@...il.com>,
	Max Krasnyansky <maxk@...lcomm.com>,
	Frederic Weisbecker <fweisbec@...il.com>, linux-mm@...ck.org
Subject: Re: [PATCH v1 3/6] workqueue: introduce schedule_on_each_cpu_cond

On 05/03/2012 08:25 PM, Gilad Ben-Yossef wrote:

> Introduce the schedule_on_each_cpu_cond() function that schedules
> a work item on each online CPU for which the supplied condition
> function returns true.
> 
> This function should be used instead of schedule_on_each_cpu()
> when only some of the CPUs have actual work to do and a predicate
> function can tell if a certain CPU does or does not have work to do,
> thus saving unneeded wakeups and schedules.
> 
> Signed-off-by: Gilad Ben-Yossef <gilad@...yossef.com>
> ---


> diff --git a/kernel/workqueue.c b/kernel/workqueue.c
> index 1c9782b..3322d30 100644
> --- a/kernel/workqueue.c
> +++ b/kernel/workqueue.c
> @@ -2828,6 +2828,43 @@ int schedule_on_each_cpu_mask(work_func_t func, const struct cpumask *mask)
>  }
> 
>  /**
> + * schedule_on_each_cpu_cond - execute a function synchronously on each
> + * online CPU for which the supplied condition function returns true
> + * @func: the function to run on the selected CPUs
> + * @cond_func: the function to call to select the CPUs
> + *
> + * schedule_on_each_cpu_cond() executes @func on each online CPU for
> + * @cond_func returns true using the system workqueue and blocks until

    ^^^
(for) which

Regards,
Srivatsa S. Bhat

> + * all CPUs have completed.
> + * schedule_on_each_cpu_cond() is very slow.
> + *
> + * RETURNS:
> + * 0 on success, -errno on failure.
> + */
> +int schedule_on_each_cpu_cond(work_func_t func, bool (*cond_func)(int cpu))
> +{
> +	int cpu, ret;
> +	cpumask_var_t mask;
> +
> +	if (unlikely(!zalloc_cpumask_var(&mask, GFP_KERNEL)))
> +		return -ENOMEM;
> +
> +	get_online_cpus();
> +
> +	for_each_online_cpu(cpu)
> +		if (cond_func(cpu))
> +			cpumask_set_cpu(cpu, mask);
> +
> +	ret = schedule_on_each_cpu_mask(func, mask);
> +
> +	put_online_cpus();
> +
> +	free_cpumask_var(mask);
> +
> +	return ret;

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