Re: [PATCH v3 03/17] xen/arm: implement node distance helpers for Arm

[Jan Beulich <jbeulich@xxxxxxxx>]

On 24.04.2023 13:02, Henry Wang wrote:
>> -----Original Message-----
>> From: Jan Beulich <jbeulich@xxxxxxxx>
>>
>> On 23.04.2023 07:36, Henry Wang wrote:
>>>> -----Original Message-----
>>>> From: Jan Beulich <jbeulich@xxxxxxxx>
>>>>>> However, looking at the code below, don't you mean to have the array
>>>>>> pre-set to all NUMA_NO_DISTANCE?
>>>>>
>>>>> ...I am a bit puzzled about why pre-setting the array to all
>>>>> NUMA_NO_DISTANCE matters here, as I think the node distance map will
>>>>> be populated when parsing the device tree anyway no matter what their
>>>>> initial values.
>>>>
>>>> From this patch alone it doesn't become clear whether indeed all array
>>>> slots (and not just ones for valid nodes) would be populated. I think
>>>> the code in the patch here would better not make itself dependent on
>>>> behavior of code added subsequently (which may change; recall that a
>>>> series may be committed in pieces).
>>>
>>> Correct, I agree. I added a numa_init_distance() function (in patch #12) to
>>> set all values to NUMA_NO_DISTANCE. The numa_init_distance() will be
>>> called in the beginning of numa_init().
>>
>> Why do you need a function for this? As said, this array can be pre-set at
>> compile time (unless I'm overlooking something).
> 
> Sorry I overlooked this comment, correct me if I am wrong, but IIUC we
> can only pre-set the 2D array to 0 at the compile time. Could you please
> elaborate a bit more about the code in your mind? Thanks!

static unsigned char __ro_after_init
node_distance_map[MAX_NUMNODES][MAX_NUMNODES] = {
    [0 ... MAX_NUMNODES - 1] = { [0 ... MAX_NUMNODES - 1] = NUMA_NO_DISTANCE }
};

or even (limiting redundancy a little)

static unsigned char __ro_after_init
node_distance_map[][MAX_NUMNODES] = {
    [0 ... MAX_NUMNODES - 1] = { [0 ... MAX_NUMNODES - 1] = NUMA_NO_DISTANCE }
};

Jan