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

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

On Wed, Mar 23, 2011 at 07:57:08PM +0100, Ferenc Wagner wrote:
> 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?

It is  not a serial driver anymore. It uses some other type of API that
does not have all of the fancy serial support. No idea actually how it
does flow control.

> 
> >> 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.

That is good. Happy to have been able to fix your problem by just talking about 
it!

BTW, haven't looked in details at the logs - little swamped right now.
> -- 
> Thanks,
> Feri.
> 
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