Re: [Xen-devel] [PATCH] xl: check for meaningful combination of sedf config file parameters

[Dario Faggioli <raistlin@xxxxxxxx>]

On Wed, 2012-06-06 at 11:35 +0100, Ian Campbell wrote:
> > diff --git a/tools/libxl/xl_cmdimpl.c b/tools/libxl/xl_cmdimpl.c
> > --- a/tools/libxl/xl_cmdimpl.c
> > +++ b/tools/libxl/xl_cmdimpl.c
> > @@ -561,6 +561,7 @@ static void parse_config_data(const char
> >      long l;
> >      XLU_Config *config;
> >      XLU_ConfigList *cpus, *vbds, *nics, *pcis, *cvfbs, *cpuids;
> > +    int opt_w = 0, opt_p = 0, opt_s = 0;
> 
> These names don't make much sense in this context.
> 
Yeah, I agree... It's just I needed something :-/

> Perhaps you can just check each interesting option against the
> corresponding LIBXL_DOAIN_SCHED_PARAM_DEFAULT? 
>
Mmm... I was mistakenly thinking these default values not to be there
yet, but I now see it. Yes, I guess I can do that.

> That might make some long
> lines. Perhaps pulling this out into a separate valid_sched_params()
> would help with that?
>
Maybe, but what to put here depends on your thought on the below...

> >      if (!xlu_cfg_get_long (config, "latency", &l, 0))
> >          b_info->sched_params.latency = l;
> >      if (!xlu_cfg_get_long (config, "extratime", &l, 0))
> >          b_info->sched_params.extratime = l;
> > +    /* The sedf scheduler needs some more consistency checking */
> > +    if (opt_w && (opt_p || opt_s)) {
> > +        fprintf(stderr, "Either specify a weight OR a period and slice\n");
> 
> Does this constrain you from setting valid combinations of credit*
> parameters? I think not since period and slice are SEDF specific.
> 
I'd say not at all, for the exact reason you're suggesting. Then, if you
ask what happens if you boot with sched=credit and then try to specify
both a cpu_weight and a period, then yes, it will kick you out.

The whole point is, period and slice are only meaningful for sedf so, if
you are using them, I take it like you meant to be using sedf, and thus
asking for a cpu_weight at the same time is wrong.

Of course, one can think at it the other way around (scheduler is
credit, so cpu_weight is fine and period and slice should be ignored).
If that is better, I can add a libxl_is_the_scheduler_credit? kind of
check to that if...

Thanks and Regards,
Dario

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

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