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

From: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
To: Peter Lieven <pl@kamp.de>
Cc: Paolo Bonzini <pbonzini@redhat.com>, John Snow <jsnow@redhat.com>,
	"qemu-devel@nongnu.org" <qemu-devel@nongnu.org>,
	qemu-block@nongnu.org
Subject: Re: [Qemu-devel] [Qemu-block] Migration sometimes fails with IDE and Qemu 2.2.1
Date: Tue, 7 Apr 2015 16:29:58 +0100	[thread overview]
Message-ID: <20150407152957.GB2287@work-vm> (raw)
In-Reply-To: <5523F38A.4090305@kamp.de>

* 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?
                                  
Dave

> 
> >
> > 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.
> 
> Thats a good point. I will check what the kernels have.
> I remember that there was sth like a problem with error handling in
> the old drivers? Paolo, you worked a lot on IDE lately. Do you remember?
> 
> Thanks,
> Peter
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK