Re: [Qemu-devel] [PATCH] migration: calculate expected_downtime with ram_bytes_remaining()

[Balamuruhan S]

On 2018-04-04 13:36, Peter Xu wrote:
> On Wed, Apr 04, 2018 at 11:55:14AM +0530, Balamuruhan S wrote:
>
> [...]
>
> > > too. So still I'll put aside the "which one is better" question.
> > >
> > > For your use case, you can have a look on either of below way to
> > > have a converged migration:
> > >
> > > - auto-converge: that's a migration capability that throttles CPU
> > >   usage of guests
> >
> > I used auto-converge option before hand and still it doesn't help
> > for migration to complete
>
> Have you digged about why?  AFAIK auto-convergence will at last absort
> merely the whole vcpu resource (99% of them maximum).  Maybe you are
> not with the best throttle values?  Or do you think that could be a
> auto-convergence bug too?

I am not sure, I will work on it to find why.

> > >
> > > - postcopy: that'll let you start the destination VM even without
> > >   transferring all the RAMs before hand
> >
> > I am seeing issue in postcopy migration between POWER8(16M) -> 
> > POWER9(1G)
> > where the hugepage size is different. I am trying to enable it but 
> > host
> > start
> > address have to be aligned with 1G page size in 
> > ram_block_discard_range(),
> > which I am debugging further to fix it.
>
> I thought the huge page size needs to be matched on both side
> currently for postcopy but I'm not sure.

you are right! it should be matched, but we need to support
POWER8(16M) -> POWER9(1G)

> CC Dave (though I think Dave's still on PTO).