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xen-devel
Re: [Xen-devel] dom0 serial input overruns
On Sun, Mar 20, 2011 at 12:02:08PM +0100, Ferenc Wagner wrote:
> (no dice on xen-users, let's try xen-devel...)
>
> Hi,
>
> I'm running a HA Xen cluster, where the dom0s are crosslinked via a null
> modem serial cable for heartbeat redundancy. This works most of the
> time, but the serial connection is very unreliable, dropping characters
If you use the hypervisor serial connection "console=com1 com1=11152..."
and re-route the console output in Linux kernel to it (console=hvc0)
does this problem disappear?
> all the time, with lot of messages like "ttyS0: 2 input overrun(s)" in
> dmesg. No such problem when running the same kernel on bare metal. The
> link is running at 9600 baud, so the system should easily cope, but it
> looks like the serial interrupt isn't serviced timely enough under Xen.
> I'm running Xen 4.0.1 now with kernel 2.6.32 (stock Debian squeeze), but
> the problem isn't specific to this setup, Xen 3.2 with kernel 2.6.18 had
> much the same issue. Raising dom0's scheduling weight didn't help much
> (or at all), pinning all domUs to CPU1-3 and vcpu0 of dom0 to CPU0
> actually made the problem worse.
>
> $ cat /proc/interrupts
> CPU0 CPU1 CPU2 CPU3
> 1: 9 0 0 0 xen-pirq-ioapic-edge i8042
> 4: 31712520 0 0 0 xen-pirq-ioapic-edge
> serial
> [...]
>
> Is there some known solution to this problem? It feels like overly big
> dom0 interrupt latency... maybe caused by the single-threaded hypervisor?
> Comments more than welcome!
> --
> Thanks,
> Feri.
>
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@xxxxxxxxxxxxxxxxxxx
> http://lists.xensource.com/xen-devel
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