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 07.04.2015 um 21:01 schrieb Dr. David Alan Gilbert:
> >* Peter Lieven (pl@kamp.de) wrote:
> >>Am 07.04.2015 um 17:29 schrieb Dr. David Alan Gilbert:
> >>>* Peter Lieven (pl@kamp.de) wrote:
> >>>>Hi David,
> >>>>
> >>>>Am 07.04.2015 um 10:43 schrieb Dr. David Alan Gilbert:
> >>>>>>>>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 ?
> >>>>Its more often than 1/10 I would say.
> >>>OK, that's not too bad - it's the 1/1000 that are really nasty to find.
> >>>In your setup, how easy would it be for you to try :
> >>>     with either 2.1 or current head?
> >>>     with a newer machine-type?
> >>>     without the cdrom?
> >>Its all possible. I can clone the system and try everything on my test systems. I hope
> >>it reproduces there.
> >Great.  I think the order I would go would be:
> >     Try head - if it works we know we've already got the fix somewhere
> >     Try 2.1  - if it works we know it's something we introduced between
> >                2.1 and 2.2.1
> >     Try a newer machine type - because pc-1.2 probably isn't tested much
> >     CDROM at the end.
> 
> Update:
>  - head -> not working
>  - 2.1.3 -> not working
>  - without CROM -> not working
>  - with head and no machine type specified -> not working
>  - with -device isa-ide -> BIOS not booting harddisk

Well, at least it's consistent....

> Will now try 1.3.1 just to be sure.
> 
> Any ideas how to debug the IDE state after migration and/or check if the issue is similar to the ATAPI IDE
> problem?

It's unlikely to be quite the same - most of the ATAPI problems were related to ATAPI
being quite separate and not saving much state.

The way I found the CDROM problems was to turn on most of the debugging in the ide and bmdma code
and on a failed migrate try and see what the state of any IO was at the point it migrated.

One other thing to check; I found the newer kernel code recovers better after
IDE problems; so on a newer guest kernel are there any log warnings about IDE problems,
even if the guests are otherwise apparently happy?

Dave

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