[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] Odd behaviour of Xen guests on multiprocessor systems ?
* Arjun <cse.syslab@xxxxxxxxx> [2006-04-25 19:57]: > I noticed an odd thing recenlty when running some experiments with several > xen guests on a multiprocessor host:- > > I was running some tests with infinite while loops inside the guests and > used xentop on the host to see what was happening. > Firstly, xentop doesn't give per-physical-cpu information for > multiprocessors, it gives VCPU information (have a separate posted query on > this). > During the tests I noticed that in some cases I, when I started the infinite > loops inside the guests, 2 guests appeared to be on the same > CPU - I inferred this because xentop would show 49.9% VCPU usage for each of > the 2 guests. In other cases, the 2 guests appeared to be on different > CPUs because xentop would show 99.9% VCPU usage for each. This state would > remain the same for however long I ran the experiment. You should run xm vcpu-list. This will give you a vcpu to cpu mapping for each domain running. [root@x460-3 ~]# xm list dom1 Name ID Mem(MiB) VCPUs State Time(s) dom1 1 768 2 -b---- 9.8 Two vcpu domain running.. [root@x460-3 ~]# xm vcpu-list dom1 Name ID VCPU CPU State Time(s) CPU Affinity dom1 1 0 2 -b- 3.3 2 dom1 1 1 3 -b- 3.0 3 I see that dom1 is using cpus 2 and 3. > > Can anyone explain why this is the case ? Once a guest VM is started on a > multiprocessor system, does it always stick to one particular physical Xen does not migrate VCPUs between physical cpus automatically. One can force a migration via the xm vcpu-pin command. [root@x460-3 ~]# xm vcpu-pin dom1 1 6 [root@x460-3 ~]# xm vcpu-list dom1 Name ID VCPU CPU State Time(s) CPU Affinity dom1 1 0 2 -b- 8.4 2 dom1 1 1 6 -b- 4.8 6 > CPU ? If so why and doesn't this have some serious implications for > provisioning for mulitple colocated VMs ? When a domain is created, Xen chooses processors with the fewest number of VCPUs present. There is certainly room for a user-space load balancer which can migrate vcpus around according to load. -- Ryan Harper Software Engineer; Linux Technology Center IBM Corp., Austin, Tx (512) 838-9253 T/L: 678-9253 ryanh@xxxxxxxxxx _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxxxxxxxx http://lists.xensource.com/xen-devel
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