[Xen-devel] Re: dom0 serial input overruns

[Ferenc Wagner <wferi@xxxxxxx>]

Ferenc Wagner <wferi@xxxxxxx> writes:

> 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...

Yes, testing confirms that bare Linux is even better, I couldn't notice
a single missing character (vs. some glitch in every couple of seconds
under Xen).

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

Who should notice this, after all?  hvc0 itself probably not, being a
virtual device.  Does the Xen serial driver detect overruns?

>> Look for a thread from 'M A Young' about keyboard issues.
>
> Long thread, I'll read through it tomorrow.

There's a good chance I'm running without the fix mentioned in the
conclusion (I'm yet to check), and my serial interrupts really hit CPU0
alone.  But my serial connection mostly works, not totally dead like in
that thread.
-- 
Thanks,
Feri.

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