Re: [PATCH RFC 0/5] support NUMA emulation for arm64

[Pierre Gondois <pierre.gondois@arm.com>]

Hello Rongwei,

On 10/12/23 15:30, Rongwei Wang wrote:
> 
> On 2023/10/12 20:37, Pierre Gondois wrote:
>> Hello Rongwei,
>>
>> On 10/12/23 04:48, Rongwei Wang wrote:
>>> A brief introduction
>>> ====================
>>>
>>> The NUMA emulation can fake more node base on a single
>>> node system, e.g.
>>>
>>> one node system:
>>>
>>> [root@localhost ~]# numactl -H
>>> available: 1 nodes (0)
>>> node 0 cpus: 0 1 2 3 4 5 6 7
>>> node 0 size: 31788 MB
>>> node 0 free: 31446 MB
>>> node distances:
>>> node   0
>>>     0:  10
>>>
>>> add numa=fake=2 (fake 2 node on each origin node):
>>>
>>> [root@localhost ~]# numactl -H
>>> available: 2 nodes (0-1)
>>> node 0 cpus: 0 1 2 3 4 5 6 7
>>> node 0 size: 15806 MB
>>> node 0 free: 15451 MB
>>> node 1 cpus: 0 1 2 3 4 5 6 7
>>> node 1 size: 16029 MB
>>> node 1 free: 15989 MB
>>> node distances:
>>> node   0   1
>>>     0:  10  10
>>>     1:  10  10
>>>
>>> As above shown, a new node has been faked. As cpus, the realization
>>> of x86 NUMA emulation is kept. Maybe each node should has 4 cores is
>>> better (not sure, next to do if so).
>>>
>>> Why do this
>>> ===========
>>>
>>> It seems has following reasons:
>>>     (1) In x86 host, apply NUMA emulation can fake more nodes environment
>>>         to test or verify some performance stuff, but arm64 only has
>>>         one method that modify ACPI table to do this. It's troublesome
>>>         more or less.
>>>     (2) Reduce competition for some locks. Here an example we found:
>>>         will-it-scale/tlb_flush1_processes -t 96 -s 10, it shows obvious
>>>         hotspot on lruvec->lock when test in single environment. What's
>>>         more, The performance improved greatly if test in two more nodes
>>>         system. The data shows below (more is better):
>>>
>>> ---------------------------------------------------------------------
>>>         threads/process |   1     |     12   |     24   | 48     |   96
>>> ---------------------------------------------------------------------
>>>         one node        | 14 1122 | 110 5372 | 111 2615 | 79 7084  |
>>> 72 4516
>>> ---------------------------------------------------------------------
>>>         numa=fake=2     | 14 1168 | 144 4848 | 215 9070 | 157 0412 |
>>> 142 3968
>>> ---------------------------------------------------------------------
>>>                         | For concurrency 12, no lruvec->lock hotspot.
>>> For 24,
>>>         hotspot         | one node has 24% hotspot on lruvec->lock, but
>>>                         | two nodes env hasn't.
>>> ---------------------------------------------------------------------
>>>
>>> As for risks (e.g. numa balance...), they need to be discussed here.
>>>
>>> Lastly, this just is a draft, I can improve next if it's acceptable.
>>
>> I'm not engaging on the utility/relevance of the patch-set, but I tried
>> them on an arm64 system with the 'numa=fake=2' parameter and could not
> 
> Sorry, my fault.
> 
> I should mention this in previous brief introduction: acpi=on numa=fake=2.
> 
> The default patch of arm64 numa initialize is numa_init() ->
> dummy_numa_init() if turn off acpi (this path has not been taken into
> account yet in this patch, next will to do).
> 
> What's more, if you test these patchset in qemu-kvm, you should add
> below parameters in the script.
> 
> object memory-backend-ram,id=mem0,size=32G \
> numa node,memdev=mem0,cpus=0-7,nodeid=0 \
> 
> (Above parameters just make sure SRAT table has NUMA configure, avoiding
> path of numa_init() -> dummy_numa_init())
> 
>> see 2 nodes being created under:
>>    /sys/devices/system/node/
>> Indeed it seems that even though numa_emulation() is moved to a generic
>> mm/numa.c file, the function is only called from:
>>    arch/x86/mm/numa.c:numa_init()
>> (or maybe I'm misinterpreting the intent of the patches).
> 
> Here drivers/base/arch_numa.c:numa_init() has called numa_emulation() (I
> guess it works if you add acpi=on :-)).

I don't see numa_emulation() being called from drivers/base/arch_numa.c:numa_init()

I have:
   $ git grep numa_emulation
   arch/x86/mm/numa.c:     numa_emulation(&numa_meminfo, numa_distance_cnt);
   arch/x86/mm/numa_internal.h:extern void __init numa_emulation(struct numa_meminfo *numa_meminfo,
   include/asm-generic/numa.h:void __init numa_emulation(struct numa_meminfo *numa_meminfo,
   mm/numa.c:/* Most of this file comes from x86/numa_emulation.c */
   mm/numa.c: * numa_emulation - Emulate NUMA nodes
   mm/numa.c:void __init numa_emulation(struct numa_meminfo *numa_meminfo, int numa_dist_cnt)
so from this, an arm64-based platform should not be able to call numa_emulation().

Is it possible to add a call to  dump_stack() in numa_emulation() to see the call stack ?

The branch I'm using is based on  v6.6-rc5 and has the 5 patches applied:
2af398a87cc7 mm/numa: migrate leftover numa emulation into mm/numa.c
c8e314fb23be mm/numa: support CONFIG_NUMA_EMU for arm64
335b7219d40e arch_numa: remove __init in early_cpu_to_node()
d9358adf1cdc mm: percpu: fix variable type of cpu
1ffbe40a00f5 mm/numa: move numa emulation APIs into generic files
94f6f0550c62 (tag: v6.6-rc5) Linux 6.6-rc5

Regards,
Pierre

> 
> 
>>
>> Also I had the following errors when building (still for arm64):
>> mm/numa.c:862:8: error: implicit declaration of function
>> 'early_cpu_to_node' is invalid in C99
>> [-Werror,-Wimplicit-function-declaration]
>>          nid = early_cpu_to_node(cpu);
> 
> It seems CONFIG_DEBUG_PER_CPU_MAPS enabled in your environment? You can
> disable CONFIG_DEBUG_PER_CPU_MAPS and test it again.
> 
> I have not test it with CONFIG_DEBUG_PER_CPU_MAPS enabled. It's very
> helpful, I will fix it next time.
> 
> If you have any questions, please let me know.
> 
> Regards,
> 
> -wrw
> 
>> ^
>> mm/numa.c:862:8: note: did you mean 'early_map_cpu_to_node'?
>> ./include/asm-generic/numa.h:37:13: note: 'early_map_cpu_to_node'
>> declared here
>> void __init early_map_cpu_to_node(unsigned int cpu, int nid);
>>              ^
>> mm/numa.c:874:3: error: implicit declaration of function
>> 'debug_cpumask_set_cpu' is invalid in C99
>> [-Werror,-Wimplicit-function-declaration]
>>                  debug_cpumask_set_cpu(cpu, nid, enable);
>>                  ^
>> mm/numa.c:874:3: note: did you mean '__cpumask_set_cpu'?
>> ./include/linux/cpumask.h:474:29: note: '__cpumask_set_cpu' declared here
>> static __always_inline void __cpumask_set_cpu(unsigned int cpu, struct
>> cpumask *dstp)
>>                              ^
>> 2 errors generated.
>>
>> Regards,
>> Pierre
>>
>>>
>>> Thanks!
>>>
>>> Rongwei Wang (5):
>>>     mm/numa: move numa emulation APIs into generic files
>>>     mm: percpu: fix variable type of cpu
>>>     arch_numa: remove __init in early_cpu_to_node()
>>>     mm/numa: support CONFIG_NUMA_EMU for arm64
>>>     mm/numa: migrate leftover numa emulation into mm/numa.c
>>>
>>>    arch/x86/Kconfig                          |   8 -
>>>    arch/x86/include/asm/numa.h               |   3 -
>>>    arch/x86/mm/Makefile                      |   1 -
>>>    arch/x86/mm/numa.c                        | 216 +-------------
>>>    arch/x86/mm/numa_internal.h               |  14 +-
>>>    drivers/base/arch_numa.c                  |   7 +-
>>>    include/asm-generic/numa.h                |  33 +++
>>>    include/linux/percpu.h                    |   2 +-
>>>    mm/Kconfig                                |   8 +
>>>    mm/Makefile                               |   1 +
>>>    arch/x86/mm/numa_emulation.c => mm/numa.c | 333 +++++++++++++++++++++-
>>>    11 files changed, 373 insertions(+), 253 deletions(-)
>>>    rename arch/x86/mm/numa_emulation.c => mm/numa.c (63%)
>>>

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