Re: [PATCH v6 for Xen 4.7 1/4] xen: enable per-VCPU parameter settings for RTDS scheduler

[Wei Liu <wei.liu2@citrix.com>]

On Thu, Mar 10, 2016 at 04:35:30PM -0600, Chong Li wrote:
> On Tue, Mar 8, 2016 at 1:09 PM, Wei Liu <wei.liu2@citrix.com> wrote:
> > On Sun, Mar 06, 2016 at 11:55:55AM -0600, Chong Li wrote:
> > [...]
> >> @@ -1163,6 +1173,96 @@ rt_dom_cntl(
> >>          }
> >>          spin_unlock_irqrestore(&prv->lock, flags);
> >>          break;
> >> +    case XEN_DOMCTL_SCHEDOP_getvcpuinfo:
> 
> >> +
> >> +            period = MICROSECS(local_sched.s.rtds.period);
> >> +            budget = MICROSECS(local_sched.s.rtds.budget);
> >> +            if ( period > RTDS_MAX_PERIOD || budget < RTDS_MIN_BUDGET ||
> >> +                          budget > period || period < RTDS_MIN_PERIOD )
> >> +            {
> >> +                rc = -EINVAL;
> >> +                break;
> >> +            }
> >> +
> >> +            /*
> >> +             * We accept period/budget less than 100 us, but will warn users about
> >> +             * the large scheduling overhead due to it
> >> +             */
> >> +            if ( period < MICROSECS(100) || budget < MICROSECS(100) )
> >> +                printk("Warning: period or budget set to less than 100us.\n"
> >> +                       "This may result in high scheduling overhead.\n");
> >> +
> >
> > I'm not the maintainer, but I think having printk here is bad idea
> > because the toolstack can then DoS the hypervisor.
> >
> >
> > Wei.
> 
> So what function should I use here? I see many LOG() calls in libxl,
> but I'm not sure whether that can be used here.
> 

IMHO you just don't log anything here. System administrator probably
won't see it anyway.

If you think this warning is really necessary, move it to xl.

Wei.

> Chong
> 
> 
> -- 
> Chong Li
> Department of Computer Science and Engineering
> Washington University in St.louis

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