Re: [Xen-devel] [PATCH] cpupools: retry cpupool-destroy if domain in cpupool is dying

[Juergen Gross <juergen.gross@xxxxxxxxxxxxxx>]

On 08.05.2014 17:10, George Dunlap wrote:
> On Wed, May 7, 2014 at 2:23 PM, Juergen Gross
> <juergen.gross@xxxxxxxxxxxxxx> wrote:
> > On 07.05.2014 15:10, George Dunlap wrote:
> > > On Wed, May 7, 2014 at 8:52 AM, Juergen Gross
> > > <juergen.gross@xxxxxxxxxxxxxx> wrote:
> > > > When a cpupool is destroyed just after the last domain has been stopped
> > > > the
> > > > domain might already be removed from the cpupool without having
> > > > decremented
> > > > the domain count of the cpupool. This will result in rejection of the
> > > > cpupool-destroy operation.
> > >
> > > I'm a bit confused.  What's the sched_move_domain() for, then?  If
> > > we're going to handle "dying domains" by doing a retry, could we just
> > > get rid of it?
> >
> > The sched_move_domain() is still needed for cases where a domain stays
> > dying for a longer time, e.g. when a dom0 process is still referencing
> > some of it's memory pages. This may be a rare situation, but being unable
> > to use a physical cpu for another cpupool just because of this case is
> > worse than this little piece of code, IMO.
> And I take it there are times when the move fails for whatever reason?
ENOMEM for example.

> Could you add a comment explaining this above the for() loop then, for
> posterity?
Could you define 'this', please? The reason for the sched_move_domain()
is mentioned in the head comment of the function (zombie domains). The
possibility of a failing sched_move_domain() is obvious by the return
value checking.


Juergen

--
Juergen Gross                 Principal Developer Operating Systems
PSO PM&D ES&S SWE OS6                  Telephone: +49 (0) 89 62060 2932
Fujitsu                                   e-mail: juergen.gross@xxxxxxxxxxxxxx
Mies-van-der-Rohe-Str. 8                Internet: ts.fujitsu.com
D-80807 Muenchen                 Company details: ts.fujitsu.com/imprint.html

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