Deep Optimization of VMM Live Upgrade - Shenming Lu, ByteDance
Channel: The Linux Foundation
Date: 2022-10-08

Deep Optimization of VMM Live Upgrade - Shenming Lu, ByteDance

The current implementations of VMM live upgrade usually choose to reuse the live migration framework, which will pause and then resume the VM, including restarting the PCI devices, during live upgrade. However, we found in practice that the stopping and starting of some external devices such as vhost-user backends (especially multiqueue DPDKs) made up a large portion of the total live upgrade downtime (could up to ~800/900ms, unacceptable for user experience), besides, the I/O downtime might be much longer than the vCPU downtime. This topic introduces our optimizations on VMM live upgrade, mainly focusing on the inefficient direct reuses of the live migration framework, such as making some external devices unaware of in live upgrade. Our experiment shows that the optimized downtime has fallen from ~900ms to ~150ms (the VM has 64 vCPUs, 128GB memory, 2 multiqueue vhost-user-net devices, 10 multiqueue vhost-user-blk devices), also without any packet loss during live upgrade.