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a=xqWC_Br6kY4A:10 a=IkcTkHD0fZMA:10 a=vUbySO9Y5rIA:10 a=GoEa3M9JfhUA:10 a=VkNPw1HP01LnGYTKEx00:22 a=VwQbUJbxAAAA:8 a=JfrnYn6hAAAA:8 a=yPCof4ZbAAAA:8 a=WlEXhbjKrYvH6h7-IdYA:9 a=QEXdDO2ut3YA:10 a=1CNFftbPRP8L7MoqJWF3:22 cc=ntf awl=host:13654 X-Proofpoint-ORIG-GUID: nVWZs_9vYxkGuX-LIrMiseBFSX2Ts64k X-Proofpoint-GUID: nVWZs_9vYxkGuX-LIrMiseBFSX2Ts64k X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwMTE1MDE2MSBTYWx0ZWRfX6jXK2DjwXW/I lB5Rbjz+9fPLpdwl5ZG0W3iFqeLOt+Oc9FbiGnjtEwfRGeteMGKzS5iuZHHW+HsEhh2Kc7kVtCi CWwRHXguL2v+CHM7rHOENqV6phXTI47NFZYqgle5SV8EAMj2zqr4tTV2dFcpuq8oMmyuQ/7PcPS E4723t6g6+ik5L7JiA5VG6Do2Uci5oFK3keSLR+lrDYVtGnB0zECFH06cKz/DkG+fqDY2xTSkJj 4joYrjaz9WeB6dVwUWJKrf3aBbApbIKC6BZ1U6zg667ROK/ptM9X5FYYs1TAb3tZQ6Dcz3XEevp 3egN+JkrGMe/tWbEfkjCPr+iZ9mMCzJ8HNd+W6Or+tjExsvraoCeQunf0URww2z62VF+hB7YALZ F/Btxe4vWP8pe3Fnv3proT1/FdP8ILf8yhLm+DhuItjMGAcJdWDUxkPwLCtgI26cA4wozNxghBM FKTm7ooX+792lharuXhabPQeMgS2SUbjKZ7T7l2w= Hi David, On 1/15/26 12:22 PM, Dongli Zhang wrote: > As noted in commit c52ffadc65e2 ("KVM: x86: Don't unnecessarily > force masterclock update on vCPU hotplug"), each unnecessary > KVM_REQ_MASTERCLOCK_UPDATE can cause the kvm-clock time to jump. > > Although that commit addressed the kvm-clock drift issue during vCPU > hotplugl there are still unnecessary KVM_REQ_MASTERCLOCK_UPDATE requests > during live migration on the target host. > > The patchset below was authored by David Woodhouse. Two of the patches aim > to avoid unnecessary KVM_REQ_MASTERCLOCK_UPDATE requests. > > [RFC PATCH v3 00/21] Cleaning up the KVM clock mess > https://lore.kernel.org/all/20240522001817.619072-1-dwmw2@infradead.org/ > > [RFC PATCH v3 10/21] KVM: x86: Fix software TSC upscaling in kvm_update_guest_time() > [RFC PATCH v3 15/21] KVM: x86: Allow KVM master clock mode when TSCs are offset from each other > > The current patchset has three patches. > > PATCH 1 is a partial copy of "[RFC PATCH v3 10/21] KVM: x86: Fix software > TSC upscaling in kvm_update_guest_time()", as Sean suggested, "Please do > this in a separate patch. There's no need to squeeze it in here, and this > change is complex/subtle enough as it is.", and David's authorship is > preserved. > Please let me know if this is inappropriate and whether I should have confirmed with you before reusing your code from the patch below, with your authorship preserved. [RFC PATCH v3 10/21] KVM: x86: Fix software TSC upscaling in kvm_update_guest_time() https://lore.kernel.org/all/20240522001817.619072-11-dwmw2@infradead.org/ The objective is to trigger a discussion on whether there is any quick, short-term solution to mitigate the kvm-clock drift issue. We can also resurrect your patchset. I have some other work in QEMU userspace. [PATCH 1/1] target/i386/kvm: account blackout downtime for kvm-clock and guest TSC https://lore.kernel.org/qemu-devel/20251009095831.46297-1-dongli.zhang@oracle.com/ The combination of changes in QEMU and this KVM patchset can make kvm-clock drift during live migration very very trivial. Thank you very much! Dongli Zhang