On Tue, Feb 03, 2026 at 11:15:15AM +0100, Lukas Straub wrote: > Like in the normal ram_load() path, put the received pages into the > colo cache and mark the pages in the bitmap so that they will be > flushed to the guest later. > > Multifd with COLO is useful to reduce the VM pause time during checkpointing > for latency sensitive workloads. In such workloads the worst-case latency > is especially important. > > Also, this is already worth it for the precopy phase as it helps with > converging. Moreover, multifd migration is the preferred way to do migration > nowadays and this allows to use multifd compression with COLO. > > Benchmark: > Cluster nodes > - Intel Xenon E5-2630 v3 > - 48Gb RAM > - 10G Ethernet > Guest > - Windows Server 2016 > - 6Gb RAM > - 4 cores > Workload > - Upload a file to the guest with SMB to simulate moderate > memory dirtying > - Measure the memory transfer time portion of each checkpoint > - 600ms COLO checkpoint interval > > Results > Plain > idle mean: 4.50ms 99per: 10.33ms > load mean: 24.30ms 99per: 78.05ms > Multifd-4 > idle mean: 6.48ms 99per: 10.41ms > load mean: 14.12ms 99per: 31.27ms > > Evaluation > While multifd has slightly higher latency when the guest idles, it is > 10ms faster under load and more importantly it's worst case latency is > less than 1/2 of plain under load as can be seen in the 99. Percentile. > > Signed-off-by: Juan Quintela <[email protected]> > Signed-off-by: Lukas Straub <[email protected]>
Reviewed-by: Peter Xu <[email protected]> -- Peter Xu
