RE: [Xen-ia64-devel] [PATCH] Fix domain reboot bug

["Zhang, Xiantao" <xiantao.zhang@xxxxxxxxx>]

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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