Re: [Xen-devel] [PATCH v2 1/4] pci: Do not ignore device's PXM information

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 07.01.15 at 16:34, <boris.ostrovsky@xxxxxxxxxx> wrote:
> On 01/07/2015 10:07 AM, Jan Beulich wrote:
>>>>> On 07.01.15 at 15:47, <andrew.cooper3@xxxxxxxxxx> wrote:
>>> On 07/01/15 14:42, Boris Ostrovsky wrote:
>>>> I kept this field as an int to be able to store NUMA_NO_NODE which I
>>>> thought to be (int)-1.
>>>>
>>>> But now I see that NUMA_NO_NODE is, in fact, 0xff but is promoted to
>>>> (int)-1 by pxm_to_node(). Given that there is a number of tests for
>>>> NUMA_NO_NODE and not for (int)-1, should we then make pxm_to_node()
>>>> return u8 as well?
>>> I noticed this as well, and found it quite counter intuitive.
>>>
>>> I would suggest fixing NUMA_NO_NODE to -1 and removing some of the
>>> type-punning.
>> I have to admit that I see no value in wasting 4 bytes for something
>> that for the foreseeable future won't exceed 1 byte.
> 
> The downside of going to u8 is that we'd be limiting number of nodes to 
> 254, which is somewhat awkward. OTOH we already do this by testing 
> nodeID against 0xff in various places.

With NODES_SHIFT being 6 and hence MAX_NUMNODES being 0x40,
we can't reach 254 right now anyway.

Jan


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