Re: [PATCH v4 11/14] arm64/numa: support HAVE_MEMORYLESS_NODES

[Ganapatrao Kulkarni]

On Wed, Jun 8, 2016 at 7:46 AM, Leizhen (ThunderTown)
<thunder.leizhen@xxxxxxxxxx> wrote:
>
>
> On 2016/6/7 22:01, Ganapatrao Kulkarni wrote:
>> On Tue, Jun 7, 2016 at 6:27 PM, Leizhen (ThunderTown)
>> <thunder.leizhen@xxxxxxxxxx> wrote:
>>>
>>>
>>> On 2016/6/7 16:31, Ganapatrao Kulkarni wrote:
>>>> On Tue, Jun 7, 2016 at 1:38 PM, Zhen Lei <thunder.leizhen@xxxxxxxxxx> wrote:
>>>>> Some numa nodes may have no memory. For example:
>>>>> 1. cpu0 on node0
>>>>> 2. cpu1 on node1
>>>>> 3. device0 access the momory from node0 and node1 take the same time.
>>>>
>>>> i am wondering, if access to both nodes is same, then why you need numa.
>>>> the example you are quoting is against the basic principle of "numa"
>>>> what is device0 here? cpu?
>>> The device0 can also be a cpu. I drew a simple diagram:
>>>
>>>   cpu0     cpu1        cpu2/device0
>>>     |        |              |
>>>     |        |              |
>>>    DDR0     DDR1    No DIMM slots or no DIMM plugged
>>>  (node0)  (node1)         (node2)
>>>
>>
>> thanks for the clarification. your example is for 3 node system, where
>> third node is memory less node.
>> do you see any issue in supporting this topology with existing code?
> If opened HAVE_MEMORYLESS_NODES, it will pick the nearest node for the cpus on
> memoryless node.

i see couple of arch enabled HAVE_MEMORYLESS_NODES, but i don't see
any code in arch specific numa code for this.
is that means the core code will take care of this?

>
> For example, in include/linux/topology.h
> #ifdef CONFIG_HAVE_MEMORYLESS_NODES
> ...
> static inline int cpu_to_mem(int cpu)
> {
>         return per_cpu(_numa_mem_, cpu);
> }
> ...
> #else
> ...
> static inline int cpu_to_mem(int cpu)
> {
>         return cpu_to_node(cpu);
> }
> ...
> #endif
>
>> I think, this use case should be supported with present code.
>>
>>>>>
>>>>> So, we can not simply classify device0 to node0 or node1, but we can
>>>>> define a node2 which distances to node0 and node1 are the same.
>>>>>
>>>>> Signed-off-by: Zhen Lei <thunder.leizhen@xxxxxxxxxx>
>>>>> ---
>>>>>  arch/arm64/Kconfig      |  4 ++++
>>>>>  arch/arm64/kernel/smp.c |  1 +
>>>>>  arch/arm64/mm/numa.c    | 43 +++++++++++++++++++++++++++++++++++++++++--
>>>>>  3 files changed, 46 insertions(+), 2 deletions(-)
>>>>>
>>>>> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
>>>>> index 05c1bf1..5904a62 100644
>>>>> --- a/arch/arm64/Kconfig
>>>>> +++ b/arch/arm64/Kconfig
>>>>> @@ -581,6 +581,10 @@ config NEED_PER_CPU_EMBED_FIRST_CHUNK
>>>>>         def_bool y
>>>>>         depends on NUMA
>>>>>
>>>>> +config HAVE_MEMORYLESS_NODES
>>>>> +       def_bool y
>>>>> +       depends on NUMA
>>>>> +
>>>>>  source kernel/Kconfig.preempt
>>>>>  source kernel/Kconfig.hz
>>>>>
>>>>> diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c
>>>>> index d099306..9e15297 100644
>>>>> --- a/arch/arm64/kernel/smp.c
>>>>> +++ b/arch/arm64/kernel/smp.c
>>>>> @@ -620,6 +620,7 @@ static void __init of_parse_and_init_cpus(void)
>>>>>                         }
>>>>>
>>>>>                         bootcpu_valid = true;
>>>>> +                       early_map_cpu_to_node(0, of_node_to_nid(dn));
>>>>>
>>>>>                         /*
>>>>>                          * cpu_logical_map has already been
>>>>> diff --git a/arch/arm64/mm/numa.c b/arch/arm64/mm/numa.c
>>>>> index df5c842..d73b0a0 100644
>>>>> --- a/arch/arm64/mm/numa.c
>>>>> +++ b/arch/arm64/mm/numa.c
>>>>> @@ -128,6 +128,14 @@ void __init early_map_cpu_to_node(unsigned int cpu, int nid)
>>>>>                 nid = 0;
>>>>>
>>>>>         cpu_to_node_map[cpu] = nid;
>>>>> +
>>>>> +       /*
>>>>> +        * We should set the numa node of cpu0 as soon as possible, because it
>>>>> +        * has already been set up online before. cpu_to_node(0) will soon be
>>>>> +        * called.
>>>>> +        */
>>>>> +       if (!cpu)
>>>>> +               set_cpu_numa_node(cpu, nid);
>>>>>  }
>>>>>
>>>>>  #ifdef CONFIG_HAVE_SETUP_PER_CPU_AREA
>>>>> @@ -215,6 +223,35 @@ int __init numa_add_memblk(int nid, u64 start, u64 end)
>>>>>         return ret;
>>>>>  }
>>>>>
>>>>> +static u64 __init alloc_node_data_from_nearest_node(int nid, const size_t size)
>>>>> +{
>>>>> +       int i, best_nid, distance;
>>>>> +       u64 pa;
>>>>> +       DECLARE_BITMAP(nodes_map, MAX_NUMNODES);
>>>>> +
>>>>> +       bitmap_zero(nodes_map, MAX_NUMNODES);
>>>>> +       bitmap_set(nodes_map, nid, 1);
>>>>> +
>>>>> +find_nearest_node:
>>>>> +       best_nid = NUMA_NO_NODE;
>>>>> +       distance = INT_MAX;
>>>>> +
>>>>> +       for_each_clear_bit(i, nodes_map, MAX_NUMNODES)
>>>>> +               if (numa_distance[nid][i] < distance) {
>>>>> +                       best_nid = i;
>>>>> +                       distance = numa_distance[nid][i];
>>>>> +               }
>>>>> +
>>>>> +       pa = memblock_alloc_nid(size, SMP_CACHE_BYTES, best_nid);
>>>>> +       if (!pa) {
>>>>> +               BUG_ON(best_nid == NUMA_NO_NODE);
>>>>> +               bitmap_set(nodes_map, best_nid, 1);
>>>>> +               goto find_nearest_node;
>>>>> +       }
>>>>> +
>>>>> +       return pa;
>>>>> +}
>>>>> +
>>
>> why do we need this function in arch specific code.
> I also considered put these code(include HAVE_SETUP_PER_CPU_AREA) into drivers/of/of_numa.c,
> but if I do that, it will make acpi numa dependent on of numa.

numa core/common code is mainly in directory mm/
drivers/of/of_numa.c implements only device tree numa binding.

>
>> dont you think common code will take care of this? when you define
>> HAVE_MEMORYLESS_NODES
>
> I have searched CONFIG_HAVE_MEMORYLESS_NODES in *.c, but did not find the relevant content.
> So maybe other ARCHs also missed this.

as mentioned above, arch code may not need any changes for this.
>
>>
>>>>>  /**
>>>>>   * Initialize NODE_DATA for a node on the local memory
>>>>>   */
>>>>> @@ -228,7 +265,9 @@ static void __init setup_node_data(int nid, u64 start_pfn, u64 end_pfn)
>>>>>         pr_info("Initmem setup node %d [mem %#010Lx-%#010Lx]\n",
>>>>>                 nid, start_pfn << PAGE_SHIFT, (end_pfn << PAGE_SHIFT) - 1);
>>>>>
>>>>> -       nd_pa = memblock_alloc_try_nid(nd_size, SMP_CACHE_BYTES, nid);
>>
>> this function try to allocate from a nid, if fails, it allocates from
>> node 0(local node).
>> this is ok for memory less node i guess.
> Yes, the function is OK, but the performance is not.
>
> Suppose there are 3 nodes:
> 1. cpu0 on node0, cpu1 on node1, cpu2 on node2.
> 2. cpu2 access the memory on node1 take 1us, but access the memory on node1 take 5us.
>    That is, distance[2,1] is shorter than distance[2,0].
> 3. And node2 is a memoryless node.
>
> So if NODE_DATA(2) allocated from node0, it will take more time than allocted from node1 at run time.
> Because NODE_DATA will be accessed at run time.
>
>>
>>>>> +       nd_pa = memblock_alloc_nid(nd_size, SMP_CACHE_BYTES, nid);
>>>>> +       if (!nd_pa)
>>>>> +               nd_pa = alloc_node_data_from_nearest_node(nid, nd_size);
>>>>>         nd = __va(nd_pa);
>>>>>
>>>>>         /* report and initialize */
>>>>> @@ -238,7 +277,7 @@ static void __init setup_node_data(int nid, u64 start_pfn, u64 end_pfn)
>>>>>         if (tnid != nid)
>>>>>                 pr_info("    NODE_DATA(%d) on node %d\n", nid, tnid);
>>>>>
>>>>> -       node_data[nid] = nd;
>>>>> +       NODE_DATA(nid) = nd;
>>>>>         memset(NODE_DATA(nid), 0, sizeof(pg_data_t));
>>>>>         NODE_DATA(nid)->node_id = nid;
>>>>>         NODE_DATA(nid)->node_start_pfn = start_pfn;
>>>>> --
>>>>> 2.5.0
>>>>>
>>>>>
>>>> Ganapat
>>>>>
>>>>> _______________________________________________
>>>>> linux-arm-kernel mailing list
>>>>> linux-arm-kernel@xxxxxxxxxxxxxxxxxxx
>>>>> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
>>>>
>>>> .
>>>>
>>>
>>
>> .
>>
>

thanks
Ganapat