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SubjectRe: [PATCH 1/2] powerpc/nodes: Ensure enough nodes avail for operations
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On 10/17/2017 12:22 PM, Michael Bringmann wrote:
>
>
> On 10/17/2017 12:02 PM, Nathan Fontenot wrote:
>> 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
>
> We only need one value from the array which is why I am using,
>
>>>>> + numnodes = of_read_number(&prop[min_common_depth], 1);
>
> With this implementation I do not need to allocate memory for
> an array, nor execute code to read all elements of the array.
>
> Michael

OK, I didn't see that you just needed a single value from the array.

In this case you could do

of_property_read_u32_index(rtas, "ibm,current-associativity-domains",
min_common_depth, &numnodes);

-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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