Re: [Xen-devel] an issue with 'xm save'

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

On Thu, Sep 27, 2012 at 01:58:19PM +0800, Zhenzhong Duan wrote:
> 
> 
> On 2012-09-26 20:35, Konrad Rzeszutek Wilk wrote:
> >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?
> In above test, I run save/restore twice, so two block processes.
> In other test, run save/restore once, there is only one block process.
> After do 'xm save', I see block process spin at line 328:
> 321   remove)
> 322     case $t in
> 323       phy)
> 324         exit 0
> 325         ;;
> 326
> 327       file)
> 328         claim_lock "block"
> 329         node=$(xenstore_read "$XENBUS_PATH/node")
> 330         losetup -d "$node"
> 331         release_lock "block"
> 332         exit 0
> 333         ;;

So with the patches in OVM - do they have this fixed? Can they be upstreamed
or are the dependent on some magic OVM sauce?

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