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xen-ia64-devel
RE: [Xen-ia64-devel] [PATCH] Fix domain reboot bug
Hi Tristan,
We have this worry too. But currently shouldn't have better solution
to solve this bug. Once SMP guest is ready, and this operation should be a
must, because VPs of target domain may run on every LP before destroying it .
Under this case, we have to flush all LP's vhpt. I think this is one of
shortcomings of vhpt per LP. :-) Maybe we can make a policy of allocating rid
range to reduce this kind of heavy operation:)
Thanks your reply.
-Xiantao
> -----Original Message-----
> From: Tristan Gingold [mailto:Tristan.Gingold@xxxxxxxx]
> Sent: 2006年3月30日 17:40
> To: Zhang, Xiantao; xen-ia64-devel@xxxxxxxxxxxxxxxxxxx
> Subject: Re: [Xen-ia64-devel] [PATCH] Fix domain reboot bug
>
> Le Jeudi 30 Mars 2006 11:25, Zhang, Xiantao a écrit :
> > Actually domain reboot issue is not caused by our previous patch to
> > solve schedule_tail, which instead helps to find a severe HOST_SMP plus
> > domain destroy bug.
> >
> > The major reason is that currently VHPT table for dom0/domU is per LP,
> > while domain destroy only issues vhpt_flush on current LP (dom0 is
> > running). So VHPT table is not flushed on the LP that destroyed domU is
> > running.
> >
> > The mechanism of domain reboot is to kill current domain and create a
> > new domain with same configuration. Since region id recycle is added
> > last time with domain destroy support, the new created domain will
> > inherit same region id as previous one. Under this case, the stale
> > entries in VHPT table will make new domU halt.
> >
> > Before applying our schedule_tail patch, domU will keep same pta value
> > as idle domain when first created where vhpt walker is disabled. Because
> > we use bvt as default scheduler, context switch never happens as long as
> > domU is runnable. That means domU will have vhpt DISABLED in whole life
> > cycle. So even vhpt on that LP is not flushed, domU still runs
> > correctly.
> >
> > So we need to send IPI to target LP to flush right vhpt table.
> > Especially, based on our previous patch for schedule_tail, domU can get
> > performance gain by enabling vhpt walker.
> If I understand the patch correctly, you flush all the vhpt when a domain is
> destroyed. Isn't it a little bit too heavy ?
>
> Tristan.
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