linux-kernel - Re: [PATCH 5/6] workqueue: Allow modifying low level unbound workqueue cpumask

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Date:	Tue, 13 May 2014 16:58:25 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Lai Jiangshan <laijs@...fujitsu.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Christoph Lameter <cl@...ux.com>,
	Kevin Hilman <khilman@...aro.org>,
	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 5/6] workqueue: Allow modifying low level unbound
 workqueue cpumask

On Thu, May 08, 2014 at 09:22:51PM +0800, Lai Jiangshan wrote:
> On Thu, May 8, 2014 at 12:37 AM, Frederic Weisbecker <fweisbec@...il.com> wrote:
> > Allow to modify the low-level unbound workqueues cpumask through
> > sysfs. This is performed by traversing the entire workqueue list
> > and calling apply_workqueue_attrs() on the unbound workqueues.
> >
> > 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>
> > ---
> >  kernel/workqueue.c | 65 ++++++++++++++++++++++++++++++++++++++++++++++++++++--
> >  1 file changed, 63 insertions(+), 2 deletions(-)
> >
> > diff --git a/kernel/workqueue.c b/kernel/workqueue.c
> > index 2aa296d..5978cee 100644
> > --- a/kernel/workqueue.c
> > +++ b/kernel/workqueue.c
> > @@ -293,7 +293,7 @@ static DEFINE_SPINLOCK(wq_mayday_lock);     /* protects wq->maydays list */
> >  static LIST_HEAD(workqueues);          /* PL: list of all workqueues */
> >  static bool workqueue_freezing;                /* PL: have wqs started freezing? */
> >
> > -static cpumask_var_t wq_unbound_cpumask;
> > +static cpumask_var_t wq_unbound_cpumask; /* PL: low level cpumask for all unbound wqs */
> >
> >  /* the per-cpu worker pools */
> >  static DEFINE_PER_CPU_SHARED_ALIGNED(struct worker_pool [NR_STD_WORKER_POOLS],
> > @@ -4084,19 +4084,80 @@ static struct bus_type wq_subsys = {
> >         .dev_groups                     = wq_sysfs_groups,
> >  };
> >
> > +static int unbounds_cpumask_apply(cpumask_var_t cpumask)
> > +{
> > +       struct workqueue_struct *wq;
> > +       int ret;
> > +
> > +       lockdep_assert_held(&wq_pool_mutex);
> > +
> > +       list_for_each_entry(wq, &workqueues, list) {
> > +               struct workqueue_attrs *attrs;
> > +
> > +               if (!(wq->flags & WQ_UNBOUND))
> > +                       continue;
> > +
> > +               attrs = wq_sysfs_prep_attrs(wq);
> > +               if (!attrs)
> > +                       return -ENOMEM;
> > +
> > +               ret = apply_workqueue_attrs_locked(wq, attrs, cpumask);
> > +               free_workqueue_attrs(attrs);
> > +               if (ret)
> > +                       break;
> > +       }
> > +
> > +       return 0;
> > +}
> > +
> > +static ssize_t unbounds_cpumask_store(struct device *dev,
> > +                                     struct device_attribute *attr,
> > +                                     const char *buf, size_t count)
> > +{
> > +       cpumask_var_t cpumask;
> > +       int ret = -EINVAL;
> > +
> > +       if (!zalloc_cpumask_var(&cpumask, GFP_KERNEL))
> > +               return -ENOMEM;
> > +
> > +       ret = cpumask_parse(buf, cpumask);
> > +       if (ret)
> > +               goto out;
> 
> 
>      cpumask_and(cpumask, cpumask, cpu_possible_mask);

Is it really useful? I mean in the end we only apply online bits.
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