Re: [PATCH 3/4] xen: credit2: improve distribution of budget (for domains with caps)

[George Dunlap <George.Dunlap@eu.citrix.com>]

On Thu, Jun 8, 2017 at 1:09 PM, Dario Faggioli
<dario.faggioli@citrix.com> wrote:
> Instead of letting the vCPU that for first tries to get

s/for//;

> some budget take it all (although temporarily), allow each
> vCPU to only get a specific quota of the total budget.
>
> This improves fairness, allows for more parallelism, and
> prevents vCPUs from not being able to get any budget (e.g.,
> because some other vCPU always comes before and gets it all)
> for one or more period, and hence starve (and couse troubles

* cause

> in guest kernels, such as livelocks, triggering ofwhatchdogs,

* 'of watchdogs' (missing space)

> etc.).
>
> Signed-off-by: Dario Faggioli <dario.faggioli@citrix.com>
> ---

> diff --git a/xen/common/sched_credit2.c b/xen/common/sched_credit2.c
> index 3f7b8f0..97efde8 100644
> --- a/xen/common/sched_credit2.c
> +++ b/xen/common/sched_credit2.c
> @@ -506,7 +506,7 @@ struct csched2_vcpu {
>
>      int credit;
>
> -    s_time_t budget;
> +    s_time_t budget, budget_quota;
>      struct list_head parked_elem;      /* On the parked_vcpus list   */
>
>      s_time_t start_time; /* When we were scheduled (used for credit) */
> @@ -1627,8 +1627,16 @@ static bool vcpu_try_to_get_budget(struct csched2_vcpu *svc)
>
>      if ( sdom->budget > 0 )
>      {
> -        svc->budget = sdom->budget;
> -        sdom->budget = 0;
> +        s_time_t budget;
> +
> +        /* Get our quote, if there's at least as much budget */

*quota

> @@ -2619,6 +2650,7 @@ csched2_dom_cntl(
>                      vcpu_schedule_unlock(lock, svc->vcpu);
>                  }
>              }
> +
>              sdom->cap = op->u.credit2.cap;

Since you'll be re-spinning, might as well move this into the previous
patch. :-)

Everything else looks good, so with those changes you can add:

Reviewed-by: George Dunlap <george.dunlap@citrix.com>

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