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Date: Thu, 18 Jan 2018 10:21:39 -0500
From: Steven Rostedt <rostedt@goodmis.org>
Subject: Re: [PATCH v5 1/2] printk: Add console owner and waiter logic to
 load balance console writes
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To: Byungchul Park <byungchul.park@lge.com>
Cc: Petr Mladek <pmladek@suse.com>, Sergey Senozhatsky <sergey.senozhatsky@gmail.com>, akpm@linux-foundation.org, linux-mm@kvack.org, Cong Wang <xiyou.wangcong@gmail.com>, Dave Hansen <dave.hansen@intel.com>, Johannes Weiner <hannes@cmpxchg.org>, Mel Gorman <mgorman@suse.de>, Michal Hocko <mhocko@kernel.org>, Vlastimil Babka <vbabka@suse.cz>, Peter Zijlstra <peterz@infradead.org>, Linus Torvalds <torvalds@linux-foundation.org>, Jan Kara <jack@suse.cz>, Mathieu Desnoyers <mathieu.desnoyers@efficios.com>, Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>, rostedt@home.goodmis.org, Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>, Tejun Heo <tj@kernel.org>, Pavel Machek <pavel@ucw.cz>, linux-kernel@vger.kernel.org, kernel-team@lge.com

On Thu, 18 Jan 2018 13:01:46 +0900
Byungchul Park <byungchul.park@lge.com> wrote:

> > I disagree. It is like a spinlock. You can say a spinlock() that is
> > blocked is also waiting for an event. That event being the owner does a
> > spin_unlock().  
> 
> That's exactly what I was saying. Excuse me but, I don't understand
> what you want to say. Could you explain more? What do you disagree?

I guess I'm confused at what you are asking for then.


> > I find your way confusing. I'm simulating a spinlock not a wait for
> > completion. A wait for completion usually initiates something then  
> 
> I used the word, *event* instead of *completion*. wait_for_completion()
> and complete() are just an example of a pair of waiter and event.
> Lock and unlock can also be another example, too.
> 
> Important thing is that who waits and who triggers the event. Using the
> pair, we can achieve various things, for examples:
> 
>     1. Synchronization like wait_for_completion() does.
>     2. Control exclusively entering into a critical area.
>     3. Whatever.
> 
> > waits for it to complete. This is trying to get into a critical area
> > but another task is currently in it. It's simulating a spinlock as far
> > as I can see.  
> 
> Anyway it's an example of "waiter for an event, and the event".
> 
> JFYI, spinning or sleeping does not matter. Those are just methods to
> achieve a wait. I know you're not talking about this though. It's JFYI.

OK, if it is just FYI.

-- Steve


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