Hello all, I am running a record and replay experiment with QEMU where I record timer events in QEMU when it starts in KVM mode and replay them when QEMU starts in TCG mode. I use the below command line to start QEMU in record mode - sudo ./qemu-system-x86_64 -m 1024 --machine pc-i440fx-2.5 -cpu qemu64,-kvmclock -enable-kvm -clock_replay mode=record,file=clock_record9.txt -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=~/os_images_for_qemu/ubuntu-16.04-desktop-amd64.qcow2,format=qcow2,if=none,id=img-direct -device virtio-blk-pci,drive=img-direct My host is running Linux kernel 5.8 with VMEXITs enabled for tsc accesses since I need to replay them as well. I use QEMU version 5.0.1. The host and guest architecture is x86-64. I save the state of the guest in QEMU by doing a "stop + savevm + continue" from the monitor. I load the guest saved state later when I do a replay. When I unpause/continue the guest, I see messages like - " Marking tsc unstable since the clock skew is too large. Switching to clocksource hpet. " I load the saved guest state in TCG mode of QEMU. My questions are as follows- 1. Is the above message anything to worry about? When I load the guest state in TCG mode, can I be certain that it will mimic the time in the guest after it was unpaused in KVM mode (during record)? 2. I cannot use kvmclock as my clocksource since I load the guest in TCG mode and QEMU TCG doesn't recognize kvmclock as one of the clock sources. Is HPET a good clocksource for the guest to fall back on? Thank you very much. Best Regards, Arnabjyoti Kalita
