[libvirt] [REPOST 0/4] Adjustment to recent cgroup/cpuset changes (for 1.3.1)

[Henning Schild]

On Wed, 13 Jan 2016 17:53:16 +0000
"Daniel P. Berrange" <berrange at redhat.com> wrote:

> On Wed, Jan 13, 2016 at 05:51:34PM +0100, Martin Kletzander wrote:
> > On Wed, Jan 13, 2016 at 07:29:46AM -0500, John Ferlan wrote:  
> > >Reposting my cgroup fixes series:
> > >
> > >http://www.redhat.com/archives/libvir-list/2016-January/msg00236.html
> > >
> > >partially because I originally forgot to CC the author (Henning
> > >Schild) of the original series for which these patch fix a couple
> > >of issues discovered during regression testing (virt-test memtune
> > >failures in Red Hat regression environment), but also to bring
> > >them up to date with the top of libvirt git.
> > >
> > >NB: I did send Henning the changes after the fact, but my resend
> > >using the same message-id skills so that replies are left in the
> > >onlist series are lacking.  Henning has looked at the first patch
> > >- with a response here:
> > >
> > >http://www.redhat.com/archives/libvir-list/2016-January/msg00443.html
> > >
> > >Finally, I think these changes should go into 1.3.1 since that's
> > >when the regression was introduced.
> > >  
> > 
> > It would be nice to have them in, I really tried reviewing them,
> > but I can't wrap my head around last two of them.  Maybe because
> > I'm already late for an appointment I have.
> > 
> > So unfortunately I have to leave you without the review for those
> > two as I really need to go, but anyone else feel free to continue.
> > And even re-check my reviews for 1 and 2 if you want.  It would be
> > a pity not to fix a regression when we could.  
> 
> I agree we need to get these into the next release, but please hold
> off from merging them. I want to re-examine Henning's original patches
> in more detail, as I have a bad feeling we might need to simply revert
> all of them and start again.

Until when do these patches need to be reviewed? The 1/4 is obvious but
the other ones need a closer look. I can just say that they do not seem
right.
I pulled virCgroupAddTask out of virCgroupNewMachine* and that should
be done. But it seems to me that the way virCgroupAddTask was called
contained important error handling that should remain in
virCgroupNewMachine.
If we only have a couple of days to the next release i would suggest
reverting my changes to give us time to figure the whole thing out.
I will have limited time to look into that until the end of the month.

But i certainly want those changes merged, or something that helps
solve/mitigate the realtime problems of the current implementation. My
changes address only a fraction of the problem. My suggestion for a
proper solution would be using the exclusive flags of cgroups, which
will require a totally different cgroup layout. Something like a
"machine.slice_excl" next to "machine.slice" with the current structure
replicated in there. Or a "top-level" exclusive cgroup per instance. So
far i only looked at the implications for cpu_exclusive, where such a
setup can work and will properly "protect" the reserved cpus from
accidential use.

Regards,
Henning