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

[Peter Xu <peterx@redhat.com>]

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?

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

-- 
Peter Xu