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Re: [Xen-devel] Re: [PATCH][HVM] fix VNIF restore failure on HVMguestwit

To: xen-devel@xxxxxxxxxxxxxxxxxxx
Subject: Re: [Xen-devel] Re: [PATCH][HVM] fix VNIF restore failure on HVMguestwith heavy workload
From: Mark Williamson <mark.williamson@xxxxxxxxxxxx>
Date: Thu, 12 Apr 2007 19:46:40 +0100
Cc: Tim Deegan <Tim.Deegan@xxxxxxxxxxxxx>, "Zhai, Edwin" <edwin.zhai@xxxxxxxxx>, Steven Hand <steven.hand@xxxxxxxxxxxx>, Ian Pratt <Ian.Pratt@xxxxxxxxxxxx>, "Zhao, Fan" <fan.zhao@xxxxxxxxx>, Keir Fraser <keir@xxxxxxxxxxxxx>
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> Secondly: there is a known issue with save/restore of ballooned domains
> (HVM or PV) where the balloning is done from within the guest (e.g.
> by echoing to /proc/xen/balloon). Since this doesn't update the memory
> target within xenstore, you'll end up 'reverting' the guest memory size to
> that last set via xm mem-set. The 'fix' is not to do that, i.e. only use
> the xm or XenAPI to request ballooning.

Any reason not to have the balloon driver write back to Xenstore if it's used 
in this way.  Or is it just waiting for a patch to do that?

Cheers,
Mark

>
> cheers,
>
> S.
>
>
>
>
> ----- Original Message -----
> From: "Zhao, Fan" <fan.zhao@xxxxxxxxx>
> To: "Keir Fraser" <keir@xxxxxxxxxxxxx>; "Zhai, Edwin"
> <edwin.zhai@xxxxxxxxx> Cc: "Tim Deegan" <Tim.Deegan@xxxxxxxxxxxxx>; "Ian
> Pratt"
> <Ian.Pratt@xxxxxxxxxxxx>; <xen-devel@xxxxxxxxxxxxxxxxxxx>
> Sent: Wednesday, April 11, 2007 5:24 PM
> Subject: RE: [Xen-devel] Re: [PATCH][HVM] fix VNIF restore failure on
> HVMguestwith heavy workload
>
>
> Hi Keir,
> I noticed that with cset 14773, if I use xm mem-set to adjust the memory of
> hvm guest with balloon driver by xm mem-set, and then save the guest, the
> xm save will fail, so does xm migrate. A white window will pop up, and the
> guest still exists through xm li. So will your great fixes also include the
> fixing for this issue? Thanks!
>
> Best regards,
> Fan
>
> -----Original Message-----
> From: xen-devel-bounces@xxxxxxxxxxxxxxxxxxx
> [mailto:xen-devel-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of Keir Fraser
> Sent: 2007Äê4ÔÂ11ÈÕ 16:57
> To: Zhai, Edwin
> Cc: Tim Deegan; Ian Pratt; xen-devel@xxxxxxxxxxxxxxxxxxx
> Subject: Re: [Xen-devel] Re: [PATCH][HVM] fix VNIF restore failure on
> HVMguest with heavy workload
>
>
> FYI, the next changeset worth testing or fixing is r14795:6e7ef794cdbc.
> I've made a *lot* of changes in the last 24 hours. I've tried a few
> save/restores under block and net load with no observed problems.
>
>  -- Keir
>
> On 11/4/07 08:20, "Zhai, Edwin" <edwin.zhai@xxxxxxxxx> wrote:
> > On Tue, Apr 10, 2007 at 08:16:04PM +0100, Keir Fraser wrote:
> >> On 10/4/07 17:47, "Zhai, Edwin" <edwin.zhai@xxxxxxxxx> wrote:
> >>> [PATCH][HVM] fix VNIF restore failure on HVM guest with heavy workload
> >>>
> >>> Signed-off-by: Zhai Edwin <edwin.zhai@xxxxxxxxx>
> >>>
> >>> VNIF has many intrs when save/restore with net workload, so need keep
> >>> handler
> >>> from intrs
> >>
> >> What happens if an interrupt is being processed during save/restore? It
> >> would be nice to know what the underlying bug is!
> >
> > If an pseudo PCI intr occurred after xen_suspend on cpu0, there is
> > definitely
> > a
> > crash. I copy this code from original PV driver code.
> >
> >> That said, it may well make sense to somehow disable interrupt handling
> >> across save/restore. Unfortunately your patch is insufficient since we
> >> could
> >> handle event-channel interrupts on any VCPU (the irq's affinity can be
> >> changed outside our control if it is routed through the virtual IOAPIC,
> >> and
> >> if e.g. the userspace irqbalance daemon is running).
> >>
> >> I wanted to use stop_machine_run() but unfortunately it isn't exported
> >> to modules. :-( irq_disable() may do the right thing for us though.
> >
> > SMP is a headache for PV drv save/restore on HVM. Even we disable intr on
> > all
> > cpus, PV driver on other cpu may still access low level service after
> > xen_suspend on cpu0.
> >
> > smp_suspend is used for PV drv on PV domain, which is not suitable for
> > HVM as
> > we
> > need the transparency to guest.
> >
> > Do we need lightweight stop_machine_run in this case, i.e. make other cpu
> > sleep?
> >
> >>  -- Keir
>
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-- 
Dave: Just a question. What use is a unicyle with no seat?  And no pedals!
Mark: To answer a question with a question: What use is a skateboard?
Dave: Skateboards have wheels.
Mark: My wheel has a wheel!

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