linux-kernel - Re: [RFC PATCH 13/14] kthread_worker: Add set_kthread_worker_user

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Message-ID: <20150729112354.GK2673@pathway.suse.cz>
Date:	Wed, 29 Jul 2015 13:23:54 +0200
From:	Petr Mladek <pmladek@...e.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Oleg Nesterov <oleg@...hat.com>,
	Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Josh Triplett <josh@...htriplett.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Jiri Kosina <jkosina@...e.cz>, Borislav Petkov <bp@...e.de>,
	Michal Hocko <mhocko@...e.cz>, linux-mm@...ck.org,
	Vlastimil Babka <vbabka@...e.cz>,
	live-patching@...r.kernel.org, linux-api@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 13/14] kthread_worker: Add
 set_kthread_worker_user_nice()

On Tue 2015-07-28 13:40:58, Tejun Heo wrote:
> On Tue, Jul 28, 2015 at 04:39:30PM +0200, Petr Mladek wrote:
> ...
> > +/*
> > + * set_kthread_worker_user_nice - set scheduling priority for the kthread worker
> > + * @worker: target kthread_worker
> > + * @nice: niceness value
> > + */
> > +void set_kthread_worker_user_nice(struct kthread_worker *worker, long nice)
> > +{
> > +	struct task_struct *task = worker->task;
> > +
> > +	WARN_ON(!task);
> > +	set_user_nice(task, nice);
> > +}
> > +EXPORT_SYMBOL(set_kthread_worker_user_nice);
> 
> kthread_worker is explcitly associated with a single kthread.  Why do
> we want to create explicit wrappers for kthread operations?  This is
> encapsulation for encapsulation's sake.  It doesn't buy us anything at
> all.  Just let the user access the associated kthread and operate on
> it.

My plan is to make the API cleaner and hide struct kthread_worker
definition into kthread.c. It would prevent anyone doing any hacks
with it. BTW, we do the same with struct workqueue_struct.

Another possibility would be to add helper function to get the
associated task struct but this might cause inconsistencies when
the worker is restarted.

Best Regards,
Petr
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