Re: suspend evetchn creation failure

[Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>]

On Tue, Mar 11, 2014 at 09:39:21AM -0700, Shriram Rajagopalan wrote:
> On Tue, Mar 11, 2014 at 4:21 AM, Ian Campbell <Ian.Campbell@citrix.com>wrote:
> 
> > On Mon, 2014-03-03 at 12:24 -0500, Prateek Sharma wrote:
> > > Hi all,
> > >       During xm save, I xc_save throws up this error :
> > > "failed to get the suspend evtchn port".
> > >       From my understanding, the port is supposed to be stored by
> > > xenstore in /local/domain/, but I can't see the port being created using
> > > xenstore-ls either.
> >
> > I think this event channel is created by the guest and written to
> > xenstore as part of support for the fast event channel based save
> > mechanism used by e.g. remus. In its absence save/suspend is triggered
> > via the traditional method of the toolstack writing commands to the
> > "control/shutdown" node.
> >
> > IIRC the fast event channel based save stuff is not in mainline kernels,
> > so the tools message is correct but harmless.
> >
> > CCing Shriram (Remus maintainer) in case I've got all the above wrong...
> >
> >
> Ian is right. Mainline kernels don't have suspend event channel.
> Unfortunately, not having suspend event channel results in a pretty big
> performance hit,
> as each suspend call takes about 7-10ms and a resume takes 2-4ms. You are
> looking
> at approx 10% loss of execution time just to suspend/resume the VM
> (assuming
> a 100ms checkpoint interval).

What is involved in implementing it?
> 
> However, OpenSUSE kernels have suspend event channel support. That said I
> have
> had issues with 3.7+ versions (IIRC), where the kernel starts crashing
> during
> recovery (which is basically a full resume).
> 
> shriram

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