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RE: [Xen-devel] RE: The caculation of the credit in credit_scheduler

To: Juergen Gross <juergen.gross@xxxxxxxxxxxxxx>
Subject: RE: [Xen-devel] RE: The caculation of the credit in credit_scheduler
From: "Jiang, Yunhong" <yunhong.jiang@xxxxxxxxx>
Date: Wed, 10 Nov 2010 13:55:07 +0800
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Cc: George Dunlap <George.Dunlap@xxxxxxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>, "Dong, Eddie" <eddie.dong@xxxxxxxxx>, "Zhang, Xiantao" <xiantao.zhang@xxxxxxxxx>
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Thread-topic: [Xen-devel] RE: The caculation of the credit in credit_scheduler

>-----Original Message-----
>From: xen-devel-bounces@xxxxxxxxxxxxxxxxxxx
>[mailto:xen-devel-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of Juergen Gross
>Sent: Wednesday, November 10, 2010 1:46 PM
>To: Jiang, Yunhong
>Cc: George Dunlap; xen-devel@xxxxxxxxxxxxxxxxxxx; Dong, Eddie; Zhang, Xiantao
>Subject: Re: [Xen-devel] RE: The caculation of the credit in credit_scheduler
>On 11/10/10 03:39, Jiang, Yunhong wrote:
>>> -----Original Message-----
>>> From: George Dunlap [mailto:George.Dunlap@xxxxxxxxxxxxx]
>>> Sent: Tuesday, November 09, 2010 10:27 PM
>>> To: Jiang, Yunhong
>>> Cc: xen-devel@xxxxxxxxxxxxxxxxxxx; Dong, Eddie; Zhang, Xiantao
>>> Subject: Re: The caculation of the credit in credit_scheduler
>>> On 05/11/10 07:06, Jiang, Yunhong wrote:
>>>> The reason is how the credit is caculated. Although the 3 HVM domains is
>>> to 2 PCPU and share the 2 CPUs, they will all get 2* 300 credit when credit
>>> That means the I/O intensive HVM domain will never be under credit, thus it 
>>> will
>>> preempt the CPU intensive whenever it is boost (i.e. after I/O access to 
>>> QEMU),
>>> it is set to be TS_UNDER only at the tick time, and then, boost again.
>>> I suspect that the real reason you're having trouble is that pinning and
>>> the credit mechanism don't work very well together.  Instead of pinning,
>>> have you tried using the cpupools interface to make a 2-cpu pool to put
>>> the VMs into?  That should allow the credit to be divided appropriately.
>> I have a quick look in the code, and seems the cpu pool should not help on 
>> such
>situation. The CPU poll only cares about the CPUs a domain can be scheduled, 
>not about the credit caculation.
>With cpupools you avoid the pinning. This will result in better credit
>calculation results.

My system is doing testing, so I can't do the experiment now, but I'm not sure 
if the cpupool will help the credit caculation.

>From the code in csched_acct() at "common/sched_credit.c", the credit_fair is 
>caculated as followed, and the creadt_fair's original value is caculated by 
>sum all pcpu's credit, without considering the cpu poll.

        credit_fair = ( ( credit_total
                          * sdom->weight
                          * sdom->active_vcpu_count )
                        + (weight_total - 1)
                      ) / weight_total;

Or did I missed anything?


>Juergen Gross                 Principal Developer Operating Systems
>TSP ES&S SWE OS6                       Telephone: +49 (0) 89 3222 2967
>Fujitsu Technology Solutions              e-mail: juergen.gross@xxxxxxxxxxxxxx
>Domagkstr. 28                           Internet: ts.fujitsu.com
>D-80807 Muenchen                 Company details:
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