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

[Atsushi SAKAI <sakaia@xxxxxxxxxxxxxx>]

Hi, Xiang

You should see the following patch.

changeset: Process event channels notifications in round-robin order.
changeset 324:  7fe1c6d02a2b
http://xenbits.xensource.com/linux-2.6.18-xen.hg?rev/7fe1c6d02a2b

Thanks
Atsushi SAKAI



"zhangxiang" <zhangxiang@xxxxxxxxxx> wrote:

> 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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