linux-kernel - Re: [PATCH v3] printk: Add console owner and waiter logic to load balance console writes

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Message-ID: <20171104031313.GA539@tigerII.localdomain>
Date:   Sat, 4 Nov 2017 12:13:13 +0900
From:   Sergey Senozhatsky <sergey.senozhatsky@...il.com>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Vlastimil Babka <vbabka@...e.cz>,
        LKML <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        akpm@...ux-foundation.org, linux-mm@...ck.org,
        Cong Wang <xiyou.wangcong@...il.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Mel Gorman <mgorman@...e.de>, Michal Hocko <mhocko@...nel.org>,
        Petr Mladek <pmladek@...e.com>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        "yuwang.yuwang" <yuwang.yuwang@...baba-inc.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Jan Kara <jack@...e.cz>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
Subject: Re: [PATCH v3] printk: Add console owner and waiter logic to load
 balance console writes

On (11/02/17 23:15), Steven Rostedt wrote:
> On Thu, 2 Nov 2017 23:16:16 +0100
> Vlastimil Babka <vbabka@...e.cz> wrote:
> 
> > > +			if (spin) {
> > > +				/* We spin waiting for the owner to release us */
> > > +				spin_acquire(&console_owner_dep_map, 0, 0, _THIS_IP_);
> > > +				/* Owner will clear console_waiter on hand off */
> > > +				while (!READ_ONCE(console_waiter))  
> > 
> > This should not be negated, right? We should spin while it's true, not
> > false.
> 
> Ug, yes. How did that not crash in my tests.

Ah, right... Good catch, Vlastimil. The V1 didn't work as expected
on my tests.

	-ss