Re: an issue with 'xm save'

[Zhenzhong Duan <zhenzhong.duan@oracle.com>]

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Konrad Rzeszutek Wilk wrote:
> On Fri, Sep 21, 2012 at 05:41:27PM +0800, Zhenzhong Duan wrote:
>    
>> Hi maintainers,
>>
>> I found there is an issue when 'xm save' a pvm guest. See below:
>>
>> When I do save then restore once, CPU(%) in xentop showed around 99%.
>> When I do that second time, CPU(%) showed 199%
>>
>> top in dom0 showed:
>>      PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND
>>     20946 root      18  -2 10984 1284  964 S 19.8  0.3   0:48.93 block
>>     4939 root      18  -2 10984 1288  964 S 19.5  0.3   1:34.68 block
>>
>> I could kill the block process, then all look normal again.
>>      
>
> What is the 'block' process? If you attach 'perf' to it do you get an idea
> of what it is spinning at?
>    
It's /etc/xen/scripts/block
I add 'set -x' to /etc/xen/scripts/block, found it blocked at claim_lock.
When domU was created first time, claim_lock/release_lock finished quickly,
when 'xm save' was called, claim_lock spin in its own while loop.
I can ensure no other domU create/save/etc happen when I test.
>    
>> xen and xen-tools are both generated with xen-unstable.
>> I tried xl, but it segfault.
>>      
>
> It segfaulted? When doing 'xl save'  or 'xl resume'? Or just allocating
> the guest?
>    
When xl create vm.cfg
>    
>> I also tried ovm3.1.1(xen-4.1.2-18.el5.1 and xen-tools-4.1.2-18.el5.1),
>> can't reproduce.
>>      
>
> So the issue is only present with Xen-unstable?
>    
Yes,  I found in /etc/xen/scripts/locking.sh of ovm3.1.1, func 
claim_lock is quite different to xen-unstable
Maybe this is why ovm3.1.1 work with save/restore.
> Did you clear _any_ older Xen libraries/tools when you installed Xen-unstable?
>    
No, I built xen and xen-tools on el5, then installed to ovm3.1.1 on 
other partition.
thanks
zduan

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