Re: [Xen-devel] [PATCH] xen: recalculate per-cpupool credits when updating timeslice

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 29.01.16 at 11:21, <JGross@xxxxxxxx> wrote:
> --- a/xen/common/sched_credit.c
> +++ b/xen/common/sched_credit.c
> @@ -1086,12 +1086,19 @@ csched_dom_cntl(
>  static inline void
>  __csched_set_tslice(struct csched_private *prv, unsigned timeslice)
>  {
> +    unsigned long flags;
> +
> +    spin_lock_irqsave(&prv->lock, flags);
> +
>      prv->tslice_ms = timeslice;
>      prv->ticks_per_tslice = CSCHED_TICKS_PER_TSLICE;
>      if ( prv->tslice_ms < prv->ticks_per_tslice )
>          prv->ticks_per_tslice = 1;
>      prv->tick_period_us = prv->tslice_ms * 1000 / prv->ticks_per_tslice;
>      prv->credits_per_tslice = CSCHED_CREDITS_PER_MSEC * prv->tslice_ms;
> +    prv->credit = prv->credits_per_tslice * prv->ncpus;
> +
> +    spin_unlock_irqrestore(&prv->lock, flags);
>  }

The added locking, which has no reason give for in the description
at all, puzzles me: I can see it being needed (and having been
missing) when called from csched_sys_cntl(), but it's not clear to
me why it would be needed when called from csched_init(). Yet
csched_sys_cntl() subsequently als updates prv->ratelimit_us,
and hence the lock would perhaps better be taken there?

Jan


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