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

[George Dunlap <George.Dunlap@xxxxxxxxxxxxx>]

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

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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