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

[Tristan Gingold <Tristan.Gingold@xxxxxxxx>]

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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