linux-kernel - Re: [BUG] Threaded printk breaks early debugging

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Message-ID: <Yqazr060OLp2Rpbk@google.com>
Date:   Mon, 13 Jun 2022 12:49:03 +0900
From:   Sergey Senozhatsky <senozhatsky@...omium.org>
To:     John Ogness <john.ogness@...utronix.de>
Cc:     Sergey Senozhatsky <senozhatsky@...omium.org>,
        Petr Mladek <pmladek@...e.com>,
        Peter Geis <pgwipeout@...il.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "open list:ARM/Rockchip SoC..." <linux-rockchip@...ts.infradead.org>
Subject: Re: [BUG] Threaded printk breaks early debugging

On (22/06/13 01:08), John Ogness wrote:
> On 2022-06-12, Sergey Senozhatsky <senozhatsky@...omium.org> wrote:
> > Should a situation when we have only one online CPU be enough of a
> > reason to do direct printing? Otherwise we might not have CPUs to
> > wakeup khtread on, e.g. when CPU that printk is in atomic section for
> > too long.
> 
> IMHO, no. Especially in that situation, we do not want printk causing
> that atomic section to become even longer. If the machine has entered
> normal operation, we want printk out of the way.

At the same time printk throttles itself in such cases: new messages are
not added at much higher pace that they are printed at. So we lower the
chances of missing messages.