Re: [Xen-devel] [PATCH 1/2] xen: credit2: avoid vCPUs to ever reach lower credits than idle

[Jürgen Groß <jgross@xxxxxxxx>]

On 12.03.20 16:26, Jan Beulich wrote:
> On 12.03.2020 14:44, Dario Faggioli wrote:
> > --- a/xen/common/sched/credit2.c
> > +++ b/xen/common/sched/credit2.c
> > @@ -234,7 +234,7 @@
> >    * units does not consume credits, and it must be lower than whatever
> >    * amount of credit 'regular' unit would end up with.
> >    */
> > -#define CSCHED2_IDLE_CREDIT          (-(1U<<30))
> > +#define CSCHED2_IDLE_CREDIT          INT_MIN
> The title saying "lower than", is "equal" actually fine? Looking
> at e.g. runq_insert() I'm getting the impression it's not.
>
> Looking at t2c_update() I'm also getting the impression that
> there's UB when the subtraction underflows. After all, if
> -1 << 30 wasn't small enough a value, I don't see why -1 << 31
> would be.
Yes, I'd limit svc->credit in t2c_update() to CSCHED2_IDLE_CREDIT+1


Juergen

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