linux-kernel - Re: [PATCH 3/4] workqueue: Create low-level unbound workqueues cpumask

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Message-ID: <7hlhiwooib.fsf@deeprootsystems.com>
Date:	Mon, 16 Mar 2015 10:12:12 -0700
From:	Kevin Hilman <khilman@...nel.org>
To:	Lai Jiangshan <laijs@...fujitsu.com>
Cc:	<linux-kernel@...r.kernel.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Christoph Lameter <cl@...ux.com>,
	Mike Galbraith <bitbucket@...ine.de>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Tejun Heo <tj@...nel.org>,
	Viresh Kumar <viresh.kumar@...aro.org>
Subject: Re: [PATCH 3/4] workqueue: Create low-level unbound workqueues cpumask

Lai Jiangshan <laijs@...fujitsu.com> writes:

> On 03/14/2015 07:49 AM, Kevin Hilman wrote:
>> Lai Jiangshan <laijs@...fujitsu.com> writes:
>> 
>>> From: Frederic Weisbecker <fweisbec@...il.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@...ux.com>
>>> Cc: Kevin Hilman <khilman@...aro.org>
>>> Cc: Lai Jiangshan <laijs@...fujitsu.com>
>>> Cc: Mike Galbraith <bitbucket@...ine.de>
>>> Cc: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
>>> Cc: Tejun Heo <tj@...nel.org>
>>> Cc: Viresh Kumar <viresh.kumar@...aro.org>
>>> Signed-off-by: Frederic Weisbecker <fweisbec@...il.com>
>>> Signed-off-by: Lai Jiangshan <laijs@...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);
>
>
> No, the default/booted wq_unbound_cpumask should be cpu_possible_mask.
>

Even for NO_HZ_FULL?  

IMO, for NO_HZ_FULL, we want the unbound workqueues to be on the
housekeeping CPU(s).

Kevin
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