Re: [Qemu-devel] [Qemu-block] Migration sometimes fails with IDE and Qemu 2.2.1

["Dr. David Alan Gilbert" <dgilbert@redhat.com>]

* Peter Lieven (pl@kamp.de) wrote:
> Am 06.04.2015 um 21:02 schrieb Peter Lieven:
> > Am 06.04.2015 um 20:50 schrieb John Snow:
> >>
> >> On 04/06/2015 02:47 PM, Peter Lieven wrote:
> >>> Hi all,
> >>>
> >>> is there a known issue in Qemu 2.2.1 where IDE stalls sometimes after a migration with Qemu 2.2.1?
> >>> The migration succeeds, but it seems that the complete I/O is hanging. This happens only sometimes
> >>> and only with extreme old Linux Guests (SLES 10 with Kernel 2.6.16) thus the IDE controller as
> >>> storage controller for the system disk.
> >>>
> >>> Maybe this sounds familiar to someone.
> >>>
> >>> Thank you,
> >>> Peter
> >>>
> >> It's news to me.
> > Okay, I was hoping that I just missed a patch or someone forgot to CC qemu-stable... :-)
> >
> >> Is this a regression?
> > I can't say we see those vServers hang sometime after migration since we changed the hypervisor from qemu-kvm-1.2.0 to qemu-2.2.0.
> >
> >
> >> Any particular workload or reproducer?
> > Workload is almost zero. I try to figure out if there is a way to trigger it.
> >
> > Maybe playing a role: Machine type is -M pc1.2 and we set -kvmclock as
> > CPU flag since kvmclock seemed to be quite buggy in 2.6.16...
> >
> > Exact cmdline is:
> > /usr/bin/qemu-2.2.1  -enable-kvm  -M pc-1.2  -nodefaults -netdev type=tap,id=guest2,script=no,downscript=no,ifname=tap2  -device e1000,netdev=guest2,mac=52:54:00:ff:00:65 -drive format=raw,file=iscsi://172.21.200.53/iqn.2001-05.com.equallogic:4-52aed6-88a7e99a4-d9e00040fdc509a3-XXX-hd0/0,if=ide,cache=writeback,aio=native  -serial null  -parallel null  -m 1024 -smp 2,sockets=1,cores=2,threads=1  -monitor tcp:0:4003,server,nowait -vnc :3 -qmp tcp:0:3003,server,nowait -name 'XXX' -boot order=c,once=dc,menu=off  -drive index=2,media=cdrom,if=ide,cache=unsafe,aio=native,readonly=on  -k de  -incoming tcp:0:5003  -pidfile /var/run/qemu/vm-146.pid  -mem-path /hugepages  -mem-prealloc  -rtc base=utc -usb -usbdevice tablet -no-hpet -vga cirrus  -cpu qemu64,-kvmclock
> >
> > Exact kernel is:
> > 2.6.16.46-0.12-smp (i think this is SLES10 or sth.)
> >
> > The machine does not hang. It seems just I/O is hanging. So you can type at the console or ping the system, but no longer login.
> >
> > Thank you,
> > Peter
> 
> Interesting observation: Migrating the vServer again seems to fix to problem (at least in one case I could test just now).
> 
> 2.6.8-24-smp is also affected.

How often does it fail - you say 'sometimes' - is it a 1/10 or a 1/1000 ?

I'm not sure at what kernel version the switch is, but newer kernels use some
code shared with the newer SATA world (libata?)  where as older kernels had
separate IDE code, so the behaviour of the two can be quite different.

Dave


Dave

> Thanks,
> Peter
> 
> 
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK