Hello all,
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