Re: [Xen-devel] [PATCH v3] AMD/intremap: Prevent use of per-device vector maps until irq logic is fixed

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 15.06.13 at 03:13, Suravee Suthikulanit <suravee.suthikulpanit@xxxxxxx> 
>>> wrote:
> On 6/10/2013 7:25 AM, Jan Beulich wrote:
> If we have to go with this solution temporary until we have the permanent 
> fix.
> I think that is okay with me.  Although, would you mind pointing out the 
> affect
> of having "per-device" vs. "global" irq vector map?  I am not quite familiar
> with the differences.

This simply controls within what group of entities (apart from the
CPU grouping enforced by the APIC model - logical/cluster/physical -
used) limits the selection of a vector: "global" means the same
vector can't be used for different IRQs at all, whereas per-device
means that the same vector can't be used for multiple IRQs within
the same device (which for MSI-X doesn't currently work, and
hence isn't useful to switch to by default).

>> (with a small coding style fixup, and with the question on
>> the usefulness of the final warning message - imo redundant with the
>> immediately preceding message that is being left untouched)
> 
> I also think the messages are quite confusing.  Actually, now that we can 
> have
> irq vector map and intremap map with different mode, we should be more 
> explicit
> in the message.
> 
> Also, the message "Not overriding irq_vector_map setting" is confusing to 
> me.
> 
> Would you mind considering the attached patch?  Here is the sample output

Actually I don't see the improvement, yet I do see at least one issue:

>    printk("AMD-Vi: Enabling %s irq vector map\n",
>        (opt_irq_vector_map == OPT_IRQ_VECTOR_MAP_PERDEV)? "per-device": 
> "global");

neglects that opt_irq_vector_map can have (at this point) three
different values.

I also certainly see no point in adjusting the already existing XSA-36
related message.

I'd also like to wait for Andrew's opinion, but right now I tend
towards going with his original patch.

In any case please remember that this is temporary and the code
this modifies will go away after 4.3 anyway (hence cosmetics
aren't that relevant).

Jan


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