[Xen-devel] Why the credit scheduler of xen-3.2.0 can ensure the I/O fairness?

["zhangxiang" <zhangxiang@xxxxxxxxxx>]

Hello, everybody:

I have recently read the paper "Scheduling I/O in Virtual Machine Monitors", which said that the credit scheduler of xen can not ensure the i/o fairness(Please see the Figure 3 in the paper). The author said that you can achieve the i/o fairness by disable the scheduler tickling, and sorting the vcpu by the value of the credit remained(Please see the relevant ppt for VEE08). I have evaluated the credit scheduler of xen-3.1.0, it does agree with the option in the paper.

 

However, when I evaluating the credit scheduler of xen-3.2.0, the results show that the scheduler can ensure the i/o fairness very well. I diff the sched_credit.c of the two versions of xen, they are the same. It seems that the credit scheduler of xen-3.2.0 does not sort the vcpu by credit or disable the scheduler tickling. So I wonder that what improvements xen have done to solove this problem?

The experiment I have done is as follows:
The system has an AMD Opteron 848 processor, 4G physical memory, and a Gigabit ethernet NIC. I run eight xen VMs, and run netperf benchmark separatly. Every VM has almost the same bandwidth of 120 Mb/s.

Thank you very much for your help.

 

Xiang ZHANG

National Research Center for Intelligent Computing Systems

Institute of Computing Technology, Chinese Academy of Sciences, Beijing,

P.R.China

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