Re: [libvirt] [PATCH] qemu: Default hwclock source for sPAPR to RTC

On 07/13/2017 05:49 PM, Cole Robinson wrote: > On 07/13/2017 04:36 AM, Kothapally Madhu Pavan wrote: >> QEMU fails to launch a sPAPR guest with clock sources other that RTC. >> Internally qemu only uses RTC timer for hwclock. This patch reports >> the right error message instead of qemu erroring out when any other >> timer other than RTC is used. >> > How does it fail exactly? Is it a qemu error message or a guest OS failure? > > If it's from qemu, and the error message is reasonably clear what hardware/xml > config option is at fauly, then these checks don't add much functional > benefit, just more code to maintain. If it's from qemu, and the error message is reasonably clear what hardware/xml config option is at fauly, then these checks don't add much functional benefit, just more code to maintain. When we use kvmclock timer in domain xml as: <clock offset='utc'> <timer name='kvmclock' present='yes'/> </clock> Domain fails to start with following error: #virsh start --console virt-tests-vm1 error: Failed to start domain virt-tests-vm1 error: internal error: process exited while connecting to monitor: 2017-04-25T09:31:58.180062Z qemu-system-ppc64: Unable to find CPU definition: qemu64 This is because the qemu cpu command line generated when kvmclock timer is used is: -cpu qemu64,+kvmclock This happens because in qemuBuildCpuCommandLine has default_model = qemu64, When I corrected the default model to "host" for ppc64 machine, qemu cpu commandline generated is: -cpu host,+kvmclock This is a valid qemu command for ppc64 machine. Now the qemu fails to start with folloeing error: qemu-system-ppc64: Expected key=value format, found +kvmclock.

Similarly when kvm-pit timer is used qemu warns as below: sudo ./qemu-system-ppc64 -name migrate_qemu -boot strict=on -device nec-usb-xhci,id=usb,bus=pci.0,addr=0xf -device spapr-vscsi,id=scsi0,reg=0x2000 -smp 1,maxcpus=4,sockets=4,cores=1,threads=1 --machine pseries,accel=kvm,kvm-type=HV,usb=off,dump-guest-core=off -m 4G,slots=32,maxmem=32G -drive file=/home/danielhb/vm_imgs/ubuntu1704.qcow2,format=qcow2,if=none,id=drive-virtio-disk0,cache=none -device virtio-blk-pci,scsi=off,bus=pci.0,addr=0x2,drive=drive-virtio-disk0,id=virtio-disk0,bootindex=1 -nographic -global kvm-pit.lost_tick_policy=discard qemu-system-ppc64: Warning: global kvm-pit.lost_tick_policy has invalid class name Basically, RTC is the only valid clocksource for sPAPR guests. For other clock sources qemu either errors out or internally considers RTC as default.

> > A general point, these types of checks should be considered for > qemuDomainDefValidate which adds the benefit of rejecting the config at XML > define time. I was of the opinion, the existing the domain definitions would fail to be parsed if I add in qemuDomainDefValidate(). Now, while I reply to you I realise, there is no way someone would have attempted to use non-RTC clock sources. So, its perfectly safe to move these checks to qemuDomainDefValidate(). Will attempt it in V2.