linux-kernel - Re: [PATCH] printk: Ratelimit messages printed by console drivers

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Message-ID: <20180420080428.622a8e7f@gandalf.local.home>
Date:   Fri, 20 Apr 2018 08:04:28 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Petr Mladek <pmladek@...e.com>
Cc:     Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        akpm@...ux-foundation.org, linux-mm@...ck.org,
        Peter Zijlstra <peterz@...radead.org>, Jan Kara <jack@...e.cz>,
        Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
        Tejun Heo <tj@...nel.org>, linux-kernel@...r.kernel.org,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>
Subject: Re: [PATCH] printk: Ratelimit messages printed by console drivers

On Fri, 20 Apr 2018 11:12:24 +0200
Petr Mladek <pmladek@...e.com> wrote:

> Yes, my number was arbitrary. The important thing is that it was long
> enough. Or do you know about an console that will not be able to write
> 100 lines within one hour?

The problem is the way rate limit works. If you print 100 lines (or
1000) in 5 seconds, then you just stopped printing from that context
for 59 minutes and 55 seconds. That's a long time to block printing.

What happens if you had a couple of NMIs go off that takes up that
time, and then you hit a bug 10 minutes later from that context. You
just lost it.

This is a magnitude larger than any other user of rate limit in the
kernel. The most common time is 5 seconds. The longest I can find is 1
minute. You are saying you want to block printing from this context for
60 minutes!

That is HUGE! I don't understand your rational for such a huge number.
What data do you have to back that up with?

-- Steve