I am running QEMU with KVM using the below command line - sudo ./qemu-system-x86_64 -m 1024 -machine pc-i440fx-3.0 -cpu qemu64,-kvmclock -accel kvm -netdev tap,id=tap1,ifname=tap0,script=no,downscript=no -device virtio-net-pci,netdev=tap1,mac=00:00:00:00:00:00 -drive file=ubuntu-16.04.server.qcow2,format=qcow2,if=none,id=img-direct -device virtio-blk-pci,drive=img-direct I can see that the current_clocksource used by the VM that is spawned is reported as "tsc". /sys/devices/system/clocksource/clocksource0$ cat current_clocksource tsc I collect a trace of the guest execution using IntelPT after running the below command - sudo ./perf kvm --guest --guestkallsyms=guest-kallsyms --guestmodules=guest-modules record -e intel_pt// -m ,65536 The IntelPT trace reveals that the function "read_hpet" gets called continuously while I expected the function "read_tsc" to be called. Does KVM change the clocksource in any way? I expect the clocksource to be set at boot time, how and why did the clocksource change later? Does KVM not support the tsc clocksource ? Note: I am using QEMU version 3.0. The guest runs a 4.4.0-116-generic linux kernel. Both my qemu host as well as the target architecture is x86_64. The host machine is also using "tsc" clocksource. Best Regards, Arnab
