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SubjectRe: [PATCH 1/2] powerpc/nodes: Ensure enough nodes avail for operations
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On 10/17/2017 11:14 AM, Michael Bringmann wrote:
> See below.
>
> On 10/16/2017 07:33 AM, Michael Ellerman wrote:
>> Michael Bringmann <mwb@linux.vnet.ibm.com> writes:
>>
>>> powerpc/nodes: On systems like PowerPC which allow 'hot-add' of CPU
>>
>> This is a powerpc-only patch, so saying "systems like PowerPC" is
>> confusing. What you should be saying is "On pseries systems".
>>
>>> or memory resources, it may occur that the new resources are to be
>>> inserted into nodes that were not used for these resources at bootup.
>>> In the kernel, any node that is used must be defined and initialized
>>> at boot.
>>>
>>> This patch extracts the value of the lowest domain level (number of
>>> allocable resources) from the "rtas" device tree property
>>> "ibm,current-associativity-domains" or the device tree property
>>
>> What is current associativity domains? I've not heard of it, where is it
>> documented, and what does it mean.
>>
>> Why would use the "current" set vs the "max"? I thought the whole point
>> was to discover the maximum possible set of nodes that could be
>> hotplugged.
>>
>>> "ibm,max-associativity-domains" to use as the maximum number of nodes
>>> to setup as possibly available in the system. This new setting will
>>> override the instruction,
>>>
>>> nodes_and(node_possible_map, node_possible_map, node_online_map);
>>>
>>> presently seen in the function arch/powerpc/mm/numa.c:initmem_init().
>>>
>>> If the property is not present at boot, no operation will be performed
>>> to define or enable additional nodes.
>>>
>>> Signed-off-by: Michael Bringmann <mwb@linux.vnet.ibm.com>
>>> ---
>>> arch/powerpc/mm/numa.c | 47 +++++++++++++++++++++++++++++++++++++++++++++++
>>> 1 file changed, 47 insertions(+)
>>>
>>> diff --git a/arch/powerpc/mm/numa.c b/arch/powerpc/mm/numa.c
>>> index ec098b3..b385cd0 100644
>>> --- a/arch/powerpc/mm/numa.c
>>> +++ b/arch/powerpc/mm/numa.c
>>> @@ -892,6 +892,51 @@ static void __init setup_node_data(int nid, u64 start_pfn, u64 end_pfn)
>>> NODE_DATA(nid)->node_spanned_pages = spanned_pages;
>>> }
>>>
>>> +static void __init node_associativity_setup(void)
>>
>> This should really be called "find_possible_nodes()" or something more
>> descriptive.
>
> Okay.
>>
>>> +{
>>> + struct device_node *rtas;
>>> +
>>> + rtas = of_find_node_by_path("/rtas");
>>> + if (rtas) {
>>
>> If you just short-circuit that return the whole function body can be
>> deintented, making it significantly more readable.
>>
>> ie:
>> + rtas = of_find_node_by_path("/rtas");
>> + if (!rtas)
>> + return;
>
> Okay.
>
>>
>>> + const __be32 *prop;
>>> + u32 len, entries, numnodes, i;
>>> +
>>> + prop = of_get_property(rtas,
>>> + "ibm,current-associativity-domains", &len);
>>
>> Please don't use of_get_property() in new code, we have much better
>> accessors these days, which do better error checking and handle the
>> endian conversions for you.
>>
>> In this case you'd use eg:
>>
>> u32 entries;
>> rc = of_property_read_u32(rtas, "ibm,current-associativity-domains", &entries);
>
> The property 'ibm,current-associativity-domains' has the same format as the property
> 'ibm,max-associativity-domains' i.e. it is an integer array. The accessor of_property_read_32,
> however, expects it to be an integer singleton value. Instead, it needs:

I think for this case where the property is an array of values you could use
of_property_count_elems_of_size() to get the number of elements in the array
and then use of_property_read_u32_array() to read the array.

-Nathan

>
>>
>>> + if (!prop || len < sizeof(unsigned int)) {
>>> + prop = of_get_property(rtas,
>>> + "ibm,max-associativity-domains", &len);
> if (!prop || len < sizeof(unsigned int))
>>> + goto endit;
>>> + }
>>> +
>>> + entries = of_read_number(prop++, 1);
>>> +
>>> + if (len < (entries * sizeof(unsigned int)))
>>> + goto endit;
>>> +
>>> + if ((0 <= min_common_depth) && (min_common_depth <= (entries-1)))
>>> + entries = min_common_depth;
>>> + else
>>> + entries -= 1;
>> ^
>> You can't just guess that will be the right entry.
>>
>> If min_common_depth is < 0 the function should have just returned
>> immediately at the top.
>
> Okay.
>
>>
>> If min_common_depth is outside the range of the property that's a buggy
>> device tree, you should print a warning and return.
>>
>>> + numnodes = of_read_number(&prop[entries], 1);
>>
>> u32 num_nodes;
>> rc = of_property_read_u32_index(rtas, "ibm,current-associativity-domains", min_common_depth, &num_nodes);
>>> +
>>> + printk(KERN_INFO "numa: Nodes = %d (mcd = %d)\n", numnodes,
>>> + min_common_depth);
>>> +
>>> + for (i = 0; i < numnodes; i++) {
>>> + if (!node_possible(i)) {
>>> + setup_node_data(i, 0, 0);
>>
>> Do we actually need to setup the NODE_DATA() yet? Doing it now ensures
>> it will not be allocated node local, which sucks.
>
> Okay.
>
>>
>>> + node_set(i, node_possible_map);
>>> + }
>>> + }
>>> + }
>>> +
>>> +endit:
>>
>> "out" would be the normal name.
>
> Okay.
>
>>
>>> + if (rtas)
>>> + of_node_put(rtas);
>>> +}
>>> +
>>> void __init initmem_init(void)
>>> {
>>> int nid, cpu;
>>> @@ -911,6 +956,8 @@ void __init initmem_init(void)
>>> */
>>
>> You need to update the comment above here which is contradicted by the
>> new function you're adding.
>
> Okay.
>
>>
>>> nodes_and(node_possible_map, node_possible_map, node_online_map);
>>>
>>> + node_associativity_setup();
>>> +
>>> for_each_online_node(nid) {
>>> unsigned long start_pfn, end_pfn;
>>>
>>
>> cheers
>>
>>
>

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