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[Xen-devel] Re: dom0 serial input overruns

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Subject: [Xen-devel] Re: dom0 serial input overruns
From: Ferenc Wagner <wferi@xxxxxxx>
Date: Tue, 22 Mar 2011 23:08:41 +0100
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In-reply-to: <20110322152710.GA27284@xxxxxxxxxxxx> (Konrad Rzeszutek Wilk's message of "Tue, 22 Mar 2011 11:27:10 -0400")
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Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx> writes:

> wferi writes:
>> the Xen (and Linux) serial console is also lossy as hell [...]
>> However, this lossage isn't accompanied by any warning.
> Oooh, strange.

I have to take this back, partly.  Although the bare linux serial console
is *much* more reliable (I couldn't trigger much visible corruption by a
simple 'while echo "                     X"; do :; done' loop, as under
Xen, even that heavily loses characters during the bootup message storm
when going through the Serial-over-LAN thingie.  Now I took that out of
the picture entirely, using a physical serial connection instead.  This
made a world of difference: bootup logs are pretty much perfect now, and
even the above while loop seldom produces a single wiggle (57600 baud).
See http://apt.niif.hu/xen_bootup.log for good example (the stray
character before "Allocated console ring" seems fully deterministic).
I'll test the same console setup under bare Linux tomorrow, maybe that
won't make a single error...

Still, these (infrequent) glitches over hvc0 go unnoticed by the system,
as far as I can tell.

> 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.

/proc/interrupts certainly agrees with this conjecture:

            CPU0       CPU1       CPU2       CPU3       
   4:     467344          0          0          0  xen-pirq-ioapic-edge  serial

> Look for a thread from 'M A Young' about keyboard issues.

Long thread, I'll read through it tomorrow.  Meanwhile, please find the
requested output at http://apt.niif.hu/xen_full_debug.log.

> .. 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)

I hope http://apt.niif.hu/apic_debug.log contains the info you need.

I doubt it's related, but on some bootups I get various errors (with
different traces but always at the same point), which don't seem to harm
the operation of the system.  Still, maybe you can make something out of
them: http://apt.niif.hu/xen_boot_errors.log.

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