Re: [Xen-devel] [PATCH 2/2] credit2: track residual from divisions done during accounting

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 26.02.13 at 18:08, George Dunlap <george.dunlap@xxxxxxxxxxxxx> wrote:
> @@ -271,16 +272,24 @@ struct csched_dom {
>  
>  /*
>   * Time-to-credit, credit-to-time.
> + * 
> + * We keep track of the "residual" time to make sure that frequent short
> + * schedules still get accounted for in the end.
> + *
>   * FIXME: Do pre-calculated division?
>   */
> -static s_time_t t2c(struct csched_runqueue_data *rqd, s_time_t time, struct 
> csched_vcpu *svc)
> +static void t2c_update(struct csched_runqueue_data *rqd, s_time_t time,
> +                          struct csched_vcpu *svc)
>  {
> -    return time * rqd->max_weight / svc->weight;
> +    uint64_t val = time * rqd->max_weight + svc->residual;
> +
> +    svc->residual = do_div(val, svc->weight);
> +    svc->credit -= val;
>  }
>  
>  static s_time_t c2t(struct csched_runqueue_data *rqd, s_time_t credit, 
> struct csched_vcpu *svc)
>  {
> -    return credit * svc->weight / rqd->max_weight;
> +    return (credit * svc->weight) / rqd->max_weight;

So you dropped the subtraction of svc->residual here - why?

And if indeed intended, the insertion of parentheses here could be
dropped?

Jan


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