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

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Message-ID: <YqceWi1524yuVITi@alley>
Date:   Mon, 13 Jun 2022 13:24:10 +0200
From:   Petr Mladek <pmladek@...e.com>
To:     Peter Geis <pgwipeout@...il.com>
Cc:     John Ogness <john.ogness@...utronix.de>,
        Sergey Senozhatsky <senozhatsky@...omium.org>,
        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 Sun 2022-06-12 19:30:27, Peter Geis wrote:
> On Sun, Jun 12, 2022 at 7:08 PM John Ogness <john.ogness@...utronix.de> wrote:
> >
> > On 2022-06-10, Peter Geis <pgwipeout@...il.com> wrote:
> > > This might be a side effect of the fact that this is on a low powered
> > > arm64 board. I noticed with threading enabled during large bursts the
> > > console drops an excessive amount of messages.

What do you mean that console drops an excessive amount of messages,
please?

Do you see "dropped XXX messages" in the console output?
Or something else?

> > > It's especially
> > > apparent during the handover from earlycon to the normal console.
> >
> > I guess you have a very small kernel buffer and are generating unusually
> > high amounts of messages? Is there a reason you cannot use a larger
> > buffer?
> 
> The buffer isn't an issue here, everything is available in dmesg when
> userspace becomes available. Instead some messages bound for the
> serial console are never output.

This is strage. The message "dropped XXX messages" is printed only
when the buffer was full and the oldest messages were overwritten
before they were pushed to the console. If "dmesg" shows all messages
it means that no messages were overwritten.

Best Regards,
Petr