linux-kernel - Re: [PATCH v9 05/12] kthread: Add kthread_create

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Date:	Mon, 20 Jun 2016 15:55:44 -0400
From:	Tejun Heo <tj@...nel.org>
To:	Petr Mladek <pmladek@...e.com>
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>, linux-api@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v9 05/12] kthread: Add kthread_create_worker*()

On Thu, Jun 16, 2016 at 01:17:24PM +0200, Petr Mladek wrote:
> Kthread workers are currently created using the classic kthread API,
> namely kthread_run(). kthread_worker_fn() is passed as the @threadfn
> parameter.
> 
> This patch defines kthread_create_worker() and
> kthread_create_worker_on_cpu() functions that hide implementation details.
> 
> They enforce using kthread_worker_fn() for the main thread. But I doubt
> that there are any plans to create any alternative. In fact, I think
> that we do not want any alternative main thread because it would be
> hard to support consistency with the rest of the kthread worker API.
> 
> The naming and function of kthread_create_worker() is inspired by
> the workqueues API like the rest of the kthread worker API.
> 
> The kthread_create_worker_on_cpu() variant is motivated by the original
> kthread_create_on_cpu(). Note that we need to bind per-CPU kthread
> workers already when they are created. It makes the life easier.
> kthread_bind() could not be used later for an already running worker.
> 
> This patch does _not_ convert existing kthread workers. The kthread worker
> API need more improvements first, e.g. a function to destroy the worker.
> 
> IMPORTANT:
> 
> kthread_create_worker_on_cpu() allows to use any format of the
> worker name, in compare with kthread_create_on_cpu(). The good thing
> is that it is more generic. The bad thing is that most users will
> need to pass the cpu number in two parameters, e.g.
> kthread_create_worker_on_cpu(cpu, "helper/%d", cpu).
> 
> To be honest, the main motivation was to avoid the need for an
> empty va_list. The only legal way was to create a helper function that
> would be called with an empty list. Other attempts caused compilation
> warnings or even errors on different architectures.
> 
> There were also other alternatives, for example, using #define or
> splitting __kthread_create_worker(). The used solution looked
> like the least ugly.
> 
> Signed-off-by: Petr Mladek <pmladek@...e.com>

Acked-by: Tejun Heo <tj@...nel.org>

Thanks.

-- 
tejun