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

  • To: xen-devel@xxxxxxxxxxxxxxxxxxx
  • From: Andy Smith <andy@xxxxxxxxxxxxxx>
  • Date: Sat, 2 Jul 2011 23:40:07 +0000
  • Delivery-date: Sat, 02 Jul 2011 16:41:02 -0700
  • List-id: Xen developer discussion <xen-devel.lists.xensource.com>
  • Openpgp: id=BF15490B; url=http://strugglers.net/~andy/pubkey.asc

Hi Keir,

On Sun, Jul 03, 2011 at 12:14:32AM +0100, Keir Fraser wrote:
> On 02/07/2011 21:04, "Andy Smith" <andy@xxxxxxxxxxxxxx> wrote:
> > 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.

Fair enough. I'm not really concerned about things being slow during
boot, more if sync_console would introduce strange latencies during
normal operation even without excessive ongoing console output.

Unfortunately I have no control over the terminal server
configuration in this instance otherwise I'd certainly be using a
higher baud rate. Having never had this problem with earlier
versions of Xen or anything else I thought I better ask.

> 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.

Thanks, I'll try that.


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