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

[George Dunlap <george.dunlap@xxxxxxxxxxxxx>]

On 07/01/2015 02:16 AM, Chen, Tiejun wrote:
> 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."

It looks like you didn't finish reading my message.  I suggest you do so:

>> 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.

 -George


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