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From: Kevin Hilman <khilman@kernel.org>
To: Lai Jiangshan <laijs@cn.fujitsu.com>
Cc: <linux-kernel@vger.kernel.org>, Frederic Weisbecker <fweisbec@gmail.com>,
        Christoph Lameter <cl@linux.com>, Mike Galbraith <bitbucket@online.de>,
        "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
        Tejun Heo <tj@kernel.org>, Viresh Kumar <viresh.kumar@linaro.org>
Subject: Re: [PATCH 3/4] workqueue: Create low-level unbound workqueues cpumask
References: <1426136412-7594-1-git-send-email-laijs@cn.fujitsu.com>
	<1426136412-7594-4-git-send-email-laijs@cn.fujitsu.com>
Date: Fri, 13 Mar 2015 16:49:53 -0700
In-Reply-To: <1426136412-7594-4-git-send-email-laijs@cn.fujitsu.com> (Lai
	Jiangshan's message of "Thu, 12 Mar 2015 13:00:11 +0800")
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Lai Jiangshan <laijs@cn.fujitsu.com> writes:

> From: Frederic Weisbecker <fweisbec@gmail.com>
>
> Create a cpumask that limit the affinity of all unbound workqueues.
> This cpumask is controlled though a file at the root of the workqueue
> sysfs directory.
>
> It works on a lower-level than the per WQ_SYSFS workqueues cpumask files
> such that the effective cpumask applied for a given unbound workqueue is
> the intersection of /sys/devices/virtual/workqueue/$WORKQUEUE/cpumask and
> the new /sys/devices/virtual/workqueue/cpumask_unbounds file.
>
> This patch implements the basic infrastructure and the read interface.
> cpumask_unbounds is initially set to cpu_possible_mask.
>
> Cc: Christoph Lameter <cl@linux.com>
> Cc: Kevin Hilman <khilman@linaro.org>
> Cc: Lai Jiangshan <laijs@cn.fujitsu.com>
> Cc: Mike Galbraith <bitbucket@online.de>
> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
> Cc: Tejun Heo <tj@kernel.org>
> Cc: Viresh Kumar <viresh.kumar@linaro.org>
> Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
> Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>

[...]

> @@ -5094,6 +5116,9 @@ static int __init init_workqueues(void)
>  
>  	WARN_ON(__alignof__(struct pool_workqueue) < __alignof__(long long));
>  
> +	BUG_ON(!alloc_cpumask_var(&wq_unbound_cpumask, GFP_KERNEL));
> +	cpumask_copy(wq_unbound_cpumask, cpu_possible_mask);
> +

As I mentioned in an earlier discussion[1], I still think this could
default too the housekeeping CPUs in the NO_HZ_FULL case:

#ifdef CONFIG_NO_HZ_FULL
	cpumask_complement(wq_unbound_cpumask, tick_nohz_full_mask);
#else
	cpumask_copy(wq_unbound_cpumask, cpu_possible_mask);
#endif

But that could also be left to a future optimization as well.

Kevin

[1] https://lkml.org/lkml/2014/2/14/666