Re: [Xen-devel] [PATCH v5 5/7] VT-d: No need to set irq affinity for posted format IRTE

["Wu, Feng" <feng.wu@xxxxxxxxx>]

> -----Original Message-----
> From: Jan Beulich [mailto:JBeulich@xxxxxxxx]
> Sent: Tuesday, October 25, 2016 4:09 PM
> To: Wu, Feng <feng.wu@xxxxxxxxx>
> Cc: andrew.cooper3@xxxxxxxxxx; dario.faggioli@xxxxxxxxxx;
> george.dunlap@xxxxxxxxxxxxx; Tian, Kevin <kevin.tian@xxxxxxxxx>; xen-
> devel@xxxxxxxxxxxxx
> Subject: RE: [PATCH v5 5/7] VT-d: No need to set irq affinity for posted 
> format
> IRTE
> 
> >>> On 25.10.16 at 03:04, <feng.wu@xxxxxxxxx> wrote:
> > I really don't get the point why you think the list is not enough. Could
> > you please explain more, thanks a lot!
> 
> I have to admit that I don't really know what else to say. Isn't it
> quite obvious that for you to suppress the actual update, _all_
> meaningful (in the given format) fields have to match? Unless
> you indeed compare all of them, you make assumptions about
> your callers only covering a subset of all possible inputs.

Well, the problem is when the current IRTE is in posted mode, and we use
this function to update the IRTE to remapped mode, we cannot compare
all the fields, since they have different format, and that is why I compare
the common field ( other fields are either posted specific or remapped 
specific),
it doesn't make sense to compare them between the two format.

Basically, we can divide the format into some category:
- Common field
- posted specific (PI related) or remapped specific (affinity related field)

The purpose here is to suppress the affinity related field, so when updating
posted IRTE to remapped IRTE and common field changes, we need update
them with the new value while suppressing the affinity related field.

Thanks,
Feng

> 
> And then I have to also say that for this simple an operation
> (comparing two IRTEs) the discussion has already gone on way
> too long.
> 
> Jan

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