Am 07.04.2015 um 20:56 schrieb John Snow: > > > On 04/07/2015 02:44 PM, Peter Lieven wrote: >> Am 07.04.2015 um 17:29 schrieb Dr. David Alan Gilbert: >>> * Peter Lieven (p...@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. >> >> Has the cdrom the power of taking down the bus? >> >> Peter >> > > I don't know if CDROM could stall the entire bus, but I suspect the reason > for asking is this: dgilbert and I had tracked down a problem previously > where during migration, outstanding requests being handled by the ATAPI code > can get lost during migration if, for instance, the user has only prepared > the command (via bmdma) but has not yet written to the register to activate > the command yet.
That sounds like it could be related. > > So if something like this happens: > > - User writes to the ATA registers to program a command > - Migration occurs > - User writes to the BMDMA register to initiate the command > > We can lose some of the state and data of the request. David had checked in a > workaround for at least ATAPI that simply coaxes the guest OS into trying the > command again to unstick it. Do you have the commit for me? > > I think we determined last time that we couldn't fix this problem without > changing the migration format, so we opted not to do it for 2.3. We had also > only noticed it with ATAPI drives, not HDDs, so a proper fix got kicked down > the road since we thought the workaround was sufficient. Maybe normally we use virtio nowadays and maybe the new kernel implementation (libata /dev/sdX) can't get locked? What I do not understand is how a second migration can unlock from this state? > > IIRC our success rate with reproducing it was something on the order of 1/50, > too. > > If you can reproduce it without a CDROM but using the BMDMA interface, that's > a good data point. If you can't reproduce it using the ISA interface, that's > a phenomenal data point and implicates BMDMA pretty heavily. To be 100% sure we are talking about the same? How would I use the ISA and how would I use the BMDMA interface? Thanks, Peter
