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

To: "Jiang, Yunhong" <yunhong.jiang@xxxxxxxxx>
Subject: [Xen-devel] Re: The caculation of the credit in credit_scheduler
From: George Dunlap <George.Dunlap@xxxxxxxxxxxxx>
Date: Tue, 09 Nov 2010 14:26:42 +0000
Cc: "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>, "Dong, Eddie" <eddie.dong@xxxxxxxxx>, "Zhang, Xiantao" <xiantao.zhang@xxxxxxxxx>
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On 05/11/10 07:06, Jiang, Yunhong wrote:
The reason is how the credit is caculated. Although the 3 HVM domains is pinned 
to 2 PCPU and share the 2 CPUs, they will all get 2* 300 credit when credit 
account. 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), and 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 didn't try credit2, so no idea if this will happen to credit2 also.

Credit2 may do better at dividing. However, it doesn't implement pinning (just ignores it). So you couldn't do your test unless you used cpupools, or limited cpus=2 to Xen's commandline.

Also, credit2 isn't yet designed to handle 64 cpus yet, so it may not work very well on a system with 64 cores.


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