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Re: [Xen-devel] Losing serial console boot output / sync_console

To: Andy Smith <andy@xxxxxxxxxxxxxx>, <xen-devel@xxxxxxxxxxxxxxxxxxx>
Subject: Re: [Xen-devel] Losing serial console boot output / sync_console
From: Keir Fraser <keir.xen@xxxxxxxxx>
Date: Sun, 03 Jul 2011 00:14:32 +0100
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Thread-topic: [Xen-devel] Losing serial console boot output / sync_console
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On 02/07/2011 21:04, "Andy Smith" <andy@xxxxxxxxxxxxxx> wrote:

> Hello,
> About two months ago I sent this email to the Xen users lists
> regarding a problem I was having losing some of my serial console
> output on boot:
> http://lists.xensource.com/archives/html/xen-users/2011-04/msg00340.html

If your serial line is very slow (I don't know why you're limited to 9600
baud -- 115200 baud at least is usually possible) and there is a lot of boot
output then you can expect some of it to be discarded. We prefer to discard
data rather than spin-wait to send it as that can indeed cause other
time-critical services to be delayed too long.

You should still get Xen output, for example if you CTRL-a three times and
use the debug keys (try 'h' to get a list of them).

If you want to capture all Xen's boot output, the safest way is to increase
the serial transmit buffer size. Try adding serial_tx_buffer=64k to the Xen
command line.

 -- Keir

> Unfortunately it got no replies.
> I was just wondering and hoping if any developers could answer the
> following questions:
> - Should I open a bug regarding the loss of serial console output on
>   boot, and;
> - Is sync_console as bad an idea as the warning suggests it is?
> I get all my serial console output if I use sync_console, but I
> haven't really put the machines under heavy load and would rather
> trade off truncated boot messages as opposed to performance under
> load.
> Cheers,
> Andy
> _______________________________________________
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> http://lists.xensource.com/xen-devel

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