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Allow disabling of kvm cpuid flags from qemu command line.
Comment 2RHEL Program Management
2010-06-20 13:43:21 UTC
This request was evaluated by Red Hat Product Management for inclusion in a Red
Hat Enterprise Linux major release. Product Management has requested further
review of this request by Red Hat Engineering, for potential inclusion in a Red
Hat Enterprise Linux Major release. This request is not yet committed for
inclusion.
I personally want to have it for debug purpose. If I suspect that there is a problem with kvmclock for instance I can't ask QE to reproduce it without kvmclock since there is not way to disable it without recompile source (disabling kvmclock from kernel command line didn't work in rhel5, haven't checked rhel6). Testing is easy: run rhel6/5 guest and check that kvmclock is in /sys/devices/system/clocksource/clocksource0/available_clocksource. Then run the same guest with -cpu qemu64,-kvmclock and check that kvmclock is not there.
According to comment4 test suggestion.
Tested on qemu-kvm-0.12.1.2-2.77.el6,whatever you boot with -kvmclock,qemu-kvm will promote "CPU feature kvmclock not found
CPU feature kvmclock not found".
Verified on qemu-kvm-0.12.1.2-2.96.el6,pass
I both tested guest rhel6/5,take rhel6 for example.
Steps:
1. boot guest with -cpu qemu64
#/usr/libexec/qemu-kvm -m 2G -smp 2 -drive file=/root/zhangjunyi/rhel6.64.qcow2,if=none,id=test,boot=on,cache=none,format=qcow2 -device virtio-blk-pci,drive=test -cpu qemu64 -monitor stdio -boot order=cdn,menu=on -netdev tap,id=hostnet0,vhost=on -device virtio-net-pci,netdev=hostnet0,id=net0,mac=22:11:22:45:66:93 -vnc :9 -qmp tcp:0:4445,server,nowait
2 in guest
cat /sys/devices/system/clocksource/clocksource0/available_clocksource
kvm-clock tsc acpi_pm
kvm-clock is here.
1. boot guest with -cpu qemu64 -kvmclock
#/usr/libexec/qemu-kvm -m 2G -smp 2 -drive file=/root/zhangjunyi/rhel6.64.qcow2,if=none,id=test,boot=on,cache=none,format=qcow2 -device virtio-blk-pci,drive=test -cpu qemu64,-kvmclock -monitor stdio -boot order=cdn,menu=on -netdev tap,id=hostnet0,vhost=on -device virtio-net-pci,netdev=hostnet0,id=net0,mac=22:11:22:45:66:93 -vnc :9 -qmp tcp:0:4445,server,nowait
2. in guest
# cat /sys/devices/system/clocksource/clocksource0/available_clocksource
tsc acpi_pm
kvmclock is not in here