From mboxrd@z Thu Jan 1 00:00:00 1970 From: Konrad Rzeszutek Wilk Subject: Re: dom0 serial input overruns Date: Sun, 20 Mar 2011 16:43:21 -0400 Message-ID: <20110320204321.GE3948@dumpdata.com> References: <87zkoq6onj.fsf@tac.ki.iif.hu> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <87zkoq6onj.fsf@tac.ki.iif.hu> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xensource.com Errors-To: xen-devel-bounces@lists.xensource.com To: Ferenc Wagner Cc: xen-devel@lists.xensource.com List-Id: xen-devel@lists.xenproject.org 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@lists.xensource.com > http://lists.xensource.com/xen-devel