linux-kernel - Re: [RFC][PATCH 1/4] printk: introduce printing kernel thread

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Message-ID: <20170323104040.GG4008@pathway.suse.cz>
Date:   Thu, 23 Mar 2017 11:40:40 +0100
From:   Petr Mladek <pmladek@...e.com>
To:     Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
Cc:     Steven Rostedt <rostedt@...dmis.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Peter Zijlstra <peterz@...radead.org>,
        "Rafael J . Wysocki" <rjw@...ysocki.net>,
        linux-kernel@...r.kernel.org,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Jan Kara <jack@...e.cz>
Subject: Re: [RFC][PATCH 1/4] printk: introduce printing kernel thread

On Thu 2017-03-23 14:12:42, Sergey Senozhatsky wrote:
> On (03/22/17 17:40), Petr Mladek wrote:
> [..]
> > > +void console_printing_thread_off(void)
> > > +{
> > > +	printk_kthread_disable++;
> > > +	barrier();
> > > +}
> > > +
> > > +/* This re-enables printk_kthread offloading. */
> > > +void console_printing_thread_on(void)
> > > +{
> > > +	barrier();
> > > +	printk_kthread_disable--;
> > > +}
> > 
> 
> one observation here is that those functions neither turn off nor
> disable printk_kthread. we mark the point after which we will not
> wake_up printk_kthread, but that does not mean that printk_kthread
> is already or soon will be inactive. it actually can be in running
> state. so the name

Yup, allow/deny might might be better than on/off.

> hm, I certainly see what you meant here, but I suspect this naming may
> be a bit misleading - "so printk_deferred_mode_off() disables printk_deferred()?"

True, sigh.

> > Also it is an already know term and a more generic name. This API
> > is used globally while the kthread is an implementation detail.
> > The offloading might be done another way in the future.
> 
> yes, this is why I avoided mentioning "printk_kthread" (directly)
> in API naming. console_printing_thread is sort of neutral (well,
> sort of). not insisting that the naming is perfect, of course.

It is too close to "printk_thread" used on different place.
So, it confuses me :-)


> the LOGLEVEL_SCHED thing is completely different tho. it tells us that
> neither of the above is safe -- both wake_up() and console_trylock()
> can potentially call into the scheduler. so I'm not sure we can easily
> replace LOGLEVEL_SCHED with `printk_kthread_disable'.

Grr, you are right. LOGLEVEL_SHED is deferred another way.

Let me do one more attempt for a generic name. What about?

    printk_console_press();    or try_harder() or push()
    printk_console_relax();

or something like this?

Best Regards,
Petr