On 01/24/2018 12:17 AM, Liang Li wrote: > We found that when doing drive mirror to a low speed shared storage, > if there was heavy BLK IO write workload in VM after the 'ready' event, > drive mirror block job can't be canceled immediately, it would keep > running until the heavy BLK IO workload stopped in the VM. This patch > fixed this issue.
I think you are breaking semantics here. Libvirt relies on 'block-job-cancel' after the 'ready' event to be a clean point-in-time snapshot, but that is only possible if there is no out-of-order pending I/O at the time the action takes place. Breaking in the middle of the loop, without using bdrv_drain(), risks leaving an inconsistent copy of data in the mirror not corresponding to any point-in-time on the source. There's ongoing work on adding async mirroring; this may be a better solution to the issue you are seeing. https://lists.gnu.org/archive/html/qemu-devel/2018-01/msg05419.html -- Eric Blake, Principal Software Engineer Red Hat, Inc. +1-919-301-3266 Virtualization: qemu.org | libvirt.org
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