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Re: [Xen-devel] Re: dom0 serial input overruns

To: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
Subject: Re: [Xen-devel] Re: dom0 serial input overruns
From: Trolle Selander <trolle.selander@xxxxxxxxx>
Date: Tue, 22 Mar 2011 11:48:08 -0400
Cc: Ferenc Wagner <wferi@xxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxx
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This issue has been around for a long time. Pinning one CPU to dom0 makes things a little better, but you can still run into lost characters on serial input at anything above 14400 bps. I was fighting this back in 2007 when I was trying to get some serial attached Point-of-Sale equipment work with Xen. Pinning dom0 & making the qemu serial device model read more aggressively from the serial device got things reliable at 9.6 & 14.4 which was all my customer at the time needed, but I any speed above that still had these described issues. From memory, it didn't make a whole lot of difference whether you let dom0 or the hypervisor handle the serial ports.


On Tue, Mar 22, 2011 at 11:27 AM, Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx> wrote:
> the boot loader).  However, this lossage isn't accompanied by any

Oooh, strange.
> warning.  I hope this answers your question.  I also run the exact same
> hardware configuration without Xen, and the Linux console is perfectly
> solid in that case (like it should under hardware flow control).  As an


> illustration, here's the serial output of querying ioapic info on the
> Xen console:

Can you do '*' in the debug console. There are some other ones that I
curious. Mainly what the IRQ 4 in your Linux dom0 maps to what vector.
Looking at your IOAPIC output:

> (XEN)  NR Log Phy Mask Trig IRR Pol Stat Dest Deli Vect:
> (XEN)  04 001 01  0    0    0   0   0    1    1    38

it should be going to the first CPU (CPU 0), but I am not sure about
the other flags... We had some issue with Xen 4.0 where IRQs below
16 would not be set correctly. It would only go to the first CPU
instead of being broadcast to all of them. Look for a thread from 'M A Young'
about keyboard issues.

.. If you boot just baremetal (so no Xen) and you give it 'apic=debug'
it should print the IOAPIC output. Can you see what this? I am
very curious to see if GSI 4 has similar looking flags set (the vector
value is going to be different)

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