linux-kernel - Re: [PATCH v5 0/2] printk: Console owner and waiter logic cleanup

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Message-ID: <20180116052301.GC13731@jagdpanzerIV>
Date:   Tue, 16 Jan 2018 14:23:01 +0900
From:   Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
To:     Petr Mladek <pmladek@...e.com>
Cc:     Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        Tejun Heo <tj@...nel.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>,
        Vlastimil Babka <vbabka@...e.cz>,
        Peter Zijlstra <peterz@...radead.org>,
        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>,
        rostedt@...e.goodmis.org, Byungchul Park <byungchul.park@....com>,
        Pavel Machek <pavel@....cz>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 0/2] printk: Console owner and waiter logic cleanup

Hi,

On (01/15/18 11:17), Petr Mladek wrote:
> Hi Sergey,
> 
> I wonder if there is still some miss understanding.
> 
> Steven and me are trying to get this patch in because we believe
> that it is a step forward. We know that it is not perfect. But
> we believe that it makes things better. In particular, it limits
> the time spent in console_unlock() in atomic context. It does
> not make it worse in preemptible context.
> 
> It does not block further improvements, including offloading
> to the kthread. We will happily discuss and review further
> improvements, it they prove to be necessary.
> 
> The advantage of this approach is that it is incremental. It should
> be easier for review and analyzing possible regressions.
> 
> What is the aim of your mails, please?
> Do you want to say that this patch might cause regressions?
> Or do you want to say that it does not solve all scenarios?
> 
> Please, answer the above questions. I am still confused.

I ACK-ed the patch set, given that I hope that we at least will
do (a)

a) remove preemption out of printk()->user critical path


---

b) the next thing would be - O(logbuf) is not a good boundary

c) the thing after that would be to - O(logbuf) boundary can be
   broken in both preemptible and non-preemptible contexts.

but (b) and (c) can wait.

	-ss