[Xen-devel] xm sched-credit problem

[Lei Lu <lulei.wm@xxxxxxxxx>]

Hi all,

I have met a very strange problem regarding CPU Cap setting. The thing
is I am trying to dynamically change the CPU cap for one guest domain,
so I try the xm sched-credit command as following

[root@llu]# xm sched-credit
Name                                ID Weight  Cap
Domain-0                             0    256    0
vm8                                    13    256   40
-----------------------------------------------------------
Okay, I want to change its CPU cap to 90%, so, I run the command
-----------------------------------------------------------
[root@llu]# xm sched-credit -d 13 -c 90
-----------------------------------------------------------
It works at first
-----------------------------------------------------------
[root@llu]# xm sched-credit
Name                                ID Weight  Cap
vm8                                    13    256   90
-----------------------------------------------------------
But after about 10 seconds, it automatically set back to 40 again.
[root@llu]# xm sched-credit
Name                                ID Weight  Cap
vm8                                    13    256   40
-------------------------------------------------------------
During those 10 seconds, it did set the CPU cap to 90 percent, which I
have confirmed by running a compute intensive inside the guest VM. I
can observer the 90% CPU through xentop in Dom-0.

I am wondering why it is set back to 40? Is it a common issue or just
for me. The version of xen is 3.3.1. The vm configuration file is
here:

kernel = "/boot/vmlinuz-2.6.18.8-xen"
ramdisk = "/boot/initrd-2.6.18.8-xen.img"
extra = "3"
extra = "xencons=tty"
memory = 1024
vcpus = 1
name = "vm8"
vif = [ 'ip=172.16.2.108,bridge=xenbr0' ]
disk = ['tap:aio:/root/local_VMs/vm8.img,sda1,w']
root = "/dev/sda1"

Best,
Lei

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