Re: [Xen-devel] [v4][PATCH 11/19] tools: introduce some new parameters to set rdm policy

["Chen, Tiejun" <tiejun.chen@xxxxxxxxx>]

On 2015/6/30 23:54, George Dunlap wrote:
> On Tue, Jun 23, 2015 at 10:57 AM, Tiejun Chen <tiejun.chen@xxxxxxxxx> wrote:
> > @@ -1450,6 +1458,11 @@ static void domcreate_attach_pci(libxl__egc *egc, 
> > libxl__multidev *multidev,
> >       }
> >
> >       for (i = 0; i < d_config->num_pcidevs; i++) {
> > +        /*
> > +         * If the rdm global policy is 'strict' we should override each device.
> > +         */
> > +        if (d_config->b_info.rdm.reserve == LIBXL_RDM_RESERVE_FLAG_STRICT)
> > +            d_config->pcidevs[i].rdm_reserve = LIBXL_RDM_RESERVE_FLAG_STRICT;
> I think I'm missing something here.
>
> 1. By default, the domain policy is RELAXED (See above,
> libxl__rdm_setdefault()).
>
> 2. By default, the policy for individual devices is STRICT (see
> libxl_pci.c:libxl__device_pci_setdefault())
>
> 3. If the domain policy is set to STRICT, this overrides per-device policy
>
> 4. If the domain policy is set to RELAXED, I don't see that having an
> effect on individual devices
This is our rule, and this is why I think you need to take a look at 
patch #00, our design and all patch head descriptions,
"Default per-device RDM policy is 'strict', while default global RDM 
policy is 'relaxed'. When both policies are specified on a given region, 
'strict' is always preferred."
Thanks
Tiejun

> If I'm correct, then #3 means it's not possible to have devices for a
> domain *default* to strict, but to be relaxed in individual instances.
> If you had five devices you wanted strict, and only one device you
> wanted to be relaxed (because you knew it didn't matter), you'd have
> to set reserved=strict for all the other devices, rather than just
> being able to set the domain setting to strict and set reserve=relaxed
> for the one.
>
> I think that both violates the principle of least surprise, and is less useful.
>
> Or did I miss something?
>
>   -George
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