Re: [Xen-devel] Is: Contention in block script when doing guest saving. Was:Re: an issue with 'xm save'

[Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx>]

Konrad Rzeszutek Wilk writes ("Is: Contention in block script when doing guest 
saving. Was:Re: [Xen-devel] an issue with 'xm save'"):
> On Fri, Sep 28, 2012 at 06:34:51PM +0800, Zhenzhong Duan wrote:
> > After replace locking.sh with OVM's, it worked.
> > But xen-tools evolved to use flock based locking currently. We can't
> > revert back.
> > It seems changeset 25595:497e2fe49455 bring the issue.
> > Finally, I came with a small patch that workaround the issue.
> 
> Ian, any thoughts on how this can be fixed properly? The locking
> is quite heavy and causes two scripts that do deal with blocks
> to spin for a long time.

The algorithm is not supposed to spin.  If it spins there is a bug, I
think.

Can you show me a transcript of the spinning happening with "set -x"
in force ?

> > diff -r d364becfb083 tools/hotplug/Linux/locking.sh
> > --- a/tools/hotplug/Linux/locking.sh    Thu Sep 20 13:31:19 2012 +0200
> > +++ b/tools/hotplug/Linux/locking.sh    Fri Sep 28 18:27:31 2012 +0800
> > @@ -66,6 +66,7 @@
> >  release_lock()
> >  {
> >      _setlockfd $1
> > +    flock -u $_lockfd
> >      rm "$_lockfile"

I'm not sure I understand how this would help.

Ian.

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