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

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 06.07.15 at 15:34, <tiejun.chen@xxxxxxxxx> wrote:
> I think we should go back here.
> 
>> I was involved in the design discussion, and from the very beginning I
>> probably saw your plan but misunderstood it.  I wouldn't be surprised if
>> some others didn't quite understand what they were agreeing to.
>>
>> This way of doing things is different than the way we do it with most
>> other options relating to pci devices (e.g., pci_permissive,
>> pci_msitranslate, pci_sieze, &c).  All of those options use a "default"
>> semantic: the domain-wide setting takes effect only if it's not set
>> locally.  If the syntax looks the same but the semantics is different,
>> many people will be confused.  If we're going to have the domain-wide
>> policy override the per-device policy, then the naming should make that
>> clear; for instance, "override=(strict|relaxed|none)", or
>> "strict_override=(1|0)".
> 
> Jan,
> 
> What about this?
> 
> This is involving our policy so please take a look at this as well.

I don't think the way things get expressed in the domain config
directly relates to what the policy is. How to best express things
in the config I'd really like to leave to the tools maintainers.

> George,
> 
> Actually we don't mean the domain-wide policy always override the 
> per-device policy, or the per-device policy always override the 
> per-device policy. Here we just take "strict" as the highest priority 
> when it conflicts in two cases. As I said previously myself may not 
> answer this very correctly but now I can recall or understand that one 
> reason is that different devices can share one RMRR entry, so its 
> possible that these two or more per-device policies are not same. So we 
> need this particular rule which is not same as before. So I still prefer 
> to keep our original implementation.
> 
> If I'm missing something or wrong, please Jan correct me.

I don't think I fully understand what you try to describe above;
instead I think the global vs per-device settings should very much
behave just like others (i.e. fallback to global if there is no per-
device setting). Furthermore, didn't we settle on not allowing
pass-through of devices sharing RMRRs unless specifically told
to by the admin (in which case part of what you write above
would seem irrelevant to me)?

Jan


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