Re: [PATCH 09/29] [HACK] tools/libxc: save/restore v2 framework

[Andrew Cooper <andrew.cooper3@citrix.com>]

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On 14/09/2014 11:23, Shriram Rajagopalan wrote:
> On Sep 11, 2014 4:08 AM, "Andrew Cooper" <andrew.cooper3@citrix.com
> <mailto:andrew.cooper3@citrix.com>> wrote:
> >
> > On 11/09/14 12:01, Ian Campbell wrote:
> > > On Thu, 2014-09-11 at 11:37 +0100, Andrew Cooper wrote:
> > >> On 11/09/14 11:34, Ian Campbell wrote:
> > >>> On Wed, 2014-09-10 at 18:10 +0100, Andrew Cooper wrote:
> > >>>> For testing purposes, the environmental variable
> "XG_MIGRATION_V2" allows the
> > >>>> two save/restore codepaths to coexist, and have a runtime switch.
> > >>>>
> > >>>> It is indended that once this series is less RFC, the v2
> framework will
> > >>>> completely replace v1.
> > >>> I think we are now at the point where this hack needs to be
> dropped from
> > >>> the series.
> > >> One problem is remus.  My plan when dropping this patch was to
> drop all
> > >> of xc_domain_{save/restore}.c as well, but without remus migration-v2
> > >> support available, this will break existing set-ups.
> > > Hrm, how is that going wrt 4.5 freeze?
> >
> > I haven’t heard seen anything since v5 of this series (for which I did
> > some quick bugfixes and released v6).
> >
>
> FYI, thats not entirely true. Yang did post a set of RFC patches for
> remus
> support in migration v2, based on your V6 series (back in July)
> http://lists.xenproject.org/archives/html/xen-devel/2014-07/msg01163.html

My apologies - it was v6 to v6.1

>
>
> It would actually be helpful if you could cc me on the patches
> relevant to Remus,
> or if there is anything specific to Remus that needs to be done. There
> are 100s of
> posts on Xen devel every day and its hard to keep track of everything
> posted to
> Xen devel.
>
>
> And I looking at your patch sets in
> http://xenbits.xen.org/gitweb/?p=people/andrewcoop/xen.git;a=shortlog;h=refs/heads/saverestore2-v6.3
>
> I see that there is no support for Remus currently. Nor can I
> differentiate which parts of the
> code fix to these "quick bug fixes" that you mentioned above. From the
> discussion over the remus rfc
> patches, I only recall a bug related to vcpu context caching. But I
> cannot delineate that specific part from
> the patches in the repo. So, if these bug fixes you are referring to
> are something else, please explain.

The bugfixes were referring to the vcpu context caching, but far more
bits needed caching than the remus series fixed.  The fixes were
necessary even in the non-remus case and there were also improvements to
receive side state machine to avoid vm corruption caused by an incorrect
send order.

I did not integrate the remus specific patches as there were outstanding
review concerns/comments.

>
>
> > I don't know, which probably means not good.
> >
>
> > >
> > >> One option might be to have legacy and v2 sitting properly
> side-by-side
> > >> in libxc for the transition period.
> > > How long do you mean? Until 4.6?
> >
>
> fwiw, I don't plan to work on remus migration v2 support until the
> remus netbuffer patches get in.
> I have been at this for almost two release cycles. Its frustrating to
> iterate on feedbacks for patch 4/11
> of a series for two months and then get a bunch of first-pass review
> for patch 6/10 at the eleventh hour
> before a feature freeze, while the rest of the series has still not
> been reviewed at all for the past 3 months.

I can appreciate your frustration on this point, and do not envy your
position.

The concern I have is that XenServer 6.5 is shipping with migrationv2 as
we absolutely need it, given the 32->64bit upgrade.  We were hoping to
get the new format committed in 4.5 to guarantee stability, but that is
looking increasingly unlikely to happen.  As a result, it will probably
have to go in early in 4.6, with extra care taken to ensure that no
incompatible changes are made as a result of further review.

~Andrew

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