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

["zhangxiang" <zhangxiang@xxxxxxxxxx>]

Hello Atsushi:

 

Thank you very much for your reply!

I have already read that patch. In the paper "Scheduling I/O in Virtual Machine Monitors", the author said that fixing event channel notification can only ensure the I/O fairness with the tickling scheduler disable, and the scheduler tickling is the culprit of the I/O unfairness even the event channel code is fixed (Please see the Section 6.1). Although Xen-3.2.0 have fixxed the event channel code, it does not disable the scheduler tickling. So I think there should be something else xen-3.2.0 has done.

Thank you again for your help.

 

Xiang ZHANG

National Research Center for Intelligent Computing Systems

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

P.R.China

 

 

---

发件人： Atsushi SAKAI

发送时间： 2008-05-26 09:56:35

收件人： zhangxiang

抄送： xen-devel

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

 

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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