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Network QoS causing high softirq - impacts on storage performance on underlying Hypervisor

Vivek kumar1709157130


Hello Folks..!!


We came across a very strange issues, I have two VMs connected with the same network on a host. Both VMS are connected via PIF to the network on XenServer. Now if i transfer one large file to the second VM with lower limit of QoS on VIF ( i.e VMs can transfer data at 200 Mbps but we have set QoS 20 Mpbs), it causes a high soft interrupts (ksoftirqd/0). Due to these high IRQs impacts on the storage performance badly.


If i increased the value of QoS on VIF ( i.e we have set QoS more then 200 Mbps ), it doesn't impact anything, no soft interrupts no loads i can see.


Network QoS are meant to be controlled the traffic but it should not impact the performance of underlying hypervisor. This issues are reproducible.


I am using XenServer 7.0. 


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Hi, Vivek:

I would run top and/or xentop during these data transfers to see the impact on the CPU load and memory. It may be just that you need to increase the memory allocated to dom0 (the main XenServer management instance). With data transfers, you put a lot more stress on resources. You could also try this using a different VIF; is the one you are using the same as the primary management interface?


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