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Re: [Xen-devel] [PATCH v2 07/10] xen: credit2: always mark a tickled pCPU as... tickled!

On Thu, 2017-02-09 at 14:59 +0100, Dario Faggioli wrote:
> In fact, whether or not a pCPU has been tickled, and is
> therefore about to re-schedule, is something we look at
> and base decisions on in various places.
> So, let's make sure that we do that basing on accurate
> information.
> While there, also tweak a little bit smt_idle_mask_clear()
> (used for implementing SMT support), so that it only alter
> the relevant cpumask when there is the actual need for this.
> (This is only for reduced overhead, behavior remains the
> same).
So, while working on other things with this series applied, I noticed
some strange behavior, for which it turned out this patch is

More specifically...

> diff --git a/xen/common/sched_credit2.c b/xen/common/sched_credit2.c
> index addee7b..bfb4891 100644
> @@ -1289,9 +1300,8 @@ runq_tickle(const struct scheduler *ops, struct
> csched2_vcpu *new, s_time_t now)
>                      sizeof(d),
>                      (unsigned char *)&d);
>      }
> -    __cpumask_set_cpu(ipid, &rqd->tickled);
> -    smt_idle_mask_clear(ipid, &rqd->smt_idle);
> -    cpu_raise_softirq(ipid, SCHEDULE_SOFTIRQ);
> +
> +    tickle_cpu(cpu, rqd);
... this, quite obviously, wants to be:

  tickle_cpu(ipid, rqd);

I'll fix this in v2.

<<This happens because I choose it to happen!>> (Raistlin Majere)
Dario Faggioli, Ph.D, http://about.me/dario.faggioli
Senior Software Engineer, Citrix Systems R&D Ltd., Cambridge (UK)

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