Re: [PATCH 1/2] powerpc/nodes: Ensure enough nodes avail for operations

[Nathan Fontenot]

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@xxxxxxxxxxxxxxxxxx> 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@xxxxxxxxxxxxxxxxxx>
>>> ---
>>>  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
>>
>>
>