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

[Jan Beulich <jbeulich@xxxxxxxx>]

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.

Jan

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