Re: an issue with 'xm save'

[Konrad Rzeszutek Wilk <konrad@kernel.org>]

On Wed, Sep 26, 2012 at 04:48:42PM +0800, Zhenzhong Duan wrote:
> 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.

OK, so how come you have two block processes? Is it b/c you have two
disks attached to the guest? The are multiple claim_lock in the shell
script - do you know where each of two threads are spinning? Are they
spinning on the same function?


> >>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

Could that be upstreamed? Perhaps that was fix that was added for this
exact reason and it just never got upstreamed?

> 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.

Excellent.
> thanks
> zduan

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