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Message-ID: <28523dc2-5fae-cf0f-0bd7-5a1978406356@loongson.cn>
Date: Thu, 17 Oct 2024 11:02:18 +0800
From: maobibo <maobibo@...ngson.cn>
To: Huacai Chen <chenhuacai@...nel.org>, Jianmin Lv <lvjianmin@...ngson.cn>
Cc: loongarch@...ts.linux.dev, linux-kernel@...r.kernel.org,
lixianglai@...ngson.cn, WANG Xuerui <kernel@...0n.name>
Subject: Re: [PATCH] LoongArch: Fix cpu hotplug issue
On 2024/10/14 下午6:11, Huacai Chen wrote:
> On Mon, Oct 14, 2024 at 6:01 PM maobibo <maobibo@...ngson.cn> wrote:
>>
>>
>>
>> On 2024/10/14 下午5:29, Huacai Chen wrote:
>>> On Mon, Oct 14, 2024 at 5:12 PM maobibo <maobibo@...ngson.cn> wrote:
>>>>
>>>>
>>>>
>>>> On 2024/10/14 下午4:23, Huacai Chen wrote:
>>>>> On Mon, Oct 14, 2024 at 4:01 PM maobibo <maobibo@...ngson.cn> wrote:
>>>>>>
>>>>>> Huacai,
>>>>>>
>>>>>> On 2024/10/14 下午3:39, Huacai Chen wrote:
>>>>>>> On Mon, Oct 14, 2024 at 3:21 PM maobibo <maobibo@...ngson.cn> wrote:
>>>>>>>>
>>>>>>>> Huacai,
>>>>>>>>
>>>>>>>> On 2024/10/14 下午3:05, Huacai Chen wrote:
>>>>>>>>> Hi, Bibo,
>>>>>>>>>
>>>>>>>>> I'm a little confused, so please correct me if I'm wrong.
>>>>>>>>>
>>>>>>>>> On Mon, Oct 14, 2024 at 2:33 PM Bibo Mao <maobibo@...ngson.cn> wrote:
>>>>>>>>>>
>>>>>>>>>> On LoongArch system, there are two places to set cpu numa node. One
>>>>>>>>>> is in arch specified function smp_prepare_boot_cpu(), the other is
>>>>>>>>>> in generic function early_numa_node_init(). The latter will overwrite
>>>>>>>>>> the numa node information.
>>>>>>>>>>
>>>>>>>>>> However for hot-added cpu, cpu_logical_map() fails to its physical
>>>>>>>>>> cpuid at beginning since it is not enabled in ACPI MADT table. So
>>>>>>>>>> function early_cpu_to_node() also fails to get its numa node for
>>>>>>>>>> hot-added cpu, and generic function early_numa_node_init() will
>>>>>>>>>> overwrite incorrect numa node.
>>>>>>>>> For hot-added cpus, we will call acpi_map_cpu() -->
>>>>>>>>> acpi_map_cpu2node() --> set_cpuid_to_node(), and set_cpuid_to_node()
>>>>>>>>> operates on __cpuid_to_node[]. So I think early_cpu_to_node() should
>>>>>>>>> be correct?
>>>>>>>>
>>>>>>>> __cpuid_to_node[] is correct which is physical cpuid to numa node,
>>>>>>>> however cpu_logical_map(cpu) is not set. It fails to get physical cpuid
>>>>>>>> from logic cpu.
>>>>>>>>
>>>>>>>> int early_cpu_to_node(int cpu)
>>>>>>>> {
>>>>>>>> int physid = cpu_logical_map(cpu);
>>>>>>>>
>>>>>>>> <<<<<<<<<<< Here physid is -1.
>>>>>>> early_cpu_to_node() is not supposed to be called after boot, and if it
>>>>>> Which calls early_cpu_to_node() after boot?
>>>>>>
>>>>>>> is really needed, I think a better solution is:
>>>>>>>
>>>>>>> diff --git a/arch/loongarch/kernel/acpi.c b/arch/loongarch/kernel/acpi.c
>>>>>>> index f1a74b80f22c..998cf45fd3b7 100644
>>>>>>> --- a/arch/loongarch/kernel/acpi.c
>>>>>>> +++ b/arch/loongarch/kernel/acpi.c
>>>>>>> @@ -311,6 +311,8 @@ static int __ref acpi_map_cpu2node(acpi_handle
>>>>>>> handle, int cpu, int physid)
>>>>>>>
>>>>>>> nid = acpi_get_node(handle);
>>>>>>> if (nid != NUMA_NO_NODE) {
>>>>>>> + __cpu_number_map[physid] = cpu;
>>>>>>> + __cpu_logical_map[cpu] = physid;
>>>>>> This does not solve the problem. The above has been done in function
>>>>>> cpu = set_processor_mask(physid, ACPI_MADT_ENABLED);
>>>>>>
>>>>>> static int set_processor_mask(u32 id, u32 flags)
>>>>>> {
>>>>>> ...
>>>>>> if (flags & ACPI_MADT_ENABLED) {
>>>>>> num_processors++;
>>>>>> set_cpu_present(cpu, true);
>>>>>> __cpu_number_map[cpuid] = cpu;
>>>>>> __cpu_logical_map[cpu] = cpuid;
>>>>>> }
>>>>>>
>>>>>> The problem is that
>>>>>> smp_prepare_boot_cpu(); /* arch-specific boot-cpu hooks */
>>>>>> <<<<<<<<<<<<<<<<
>>>>>> set_cpu_numa_node() is called in function smp_prepare_boot_cpu()
>>>>>>
>>>>>> early_numa_node_init();
>>>>>>
>>>>>> static void __init early_numa_node_init(void)
>>>>>> {
>>>>>> #ifdef CONFIG_USE_PERCPU_NUMA_NODE_ID
>>>>>> #ifndef cpu_to_node
>>>>>> int cpu;
>>>>>>
>>>>>> /* The early_cpu_to_node() should be ready here. */
>>>>>> for_each_possible_cpu(cpu)
>>>>>> set_cpu_numa_node(cpu, early_cpu_to_node(cpu));
>>>>>> <<<<<<<<<<<<<<<<
>>>>>> * however here early_cpu_to_node is -1, so that cpu_to_node(cpu) will
>>>>>> always return -1 in late. *, which causes cpu hotadd problem.
>>>>> Still confused. For ACPI_MADT_ENABLED cpus, everything is right after
>>>>> early_numa_node_init(). For !ACPI_MADT_ENABLED cpus, cpu_to_node()
>>>>> returns -1 after early_numa_node_init() and before hot-add, but if
>>>>> acpi_map_cpu() do things right, cpu_to_node() should still work well
>>>>> after hot-add.
>>>> yes, if "_PXM" information for hot-add cpu handle exist, it works well.
>>>>
>>>> However if "_PXM" information does not exist, it falls back to legacy
>>>> method from smp_prepare_boot_cpu(). However cpu_numa_node information is
>>>> overwritten with -1 by later function early_numa_node_init().
>>> OK, now I finally get the key point. But no _PXM should be treated as
>>> a BIOS bug, right?
>> Currently if no numa information is added in qemu command line, there
>> will be no "_PXM" information for hot-added cpu. Such as for this command:
>> qemu-system-loongarch64 -m 4096 -smp
>> 1,maxcpus=4,sockets=1,cores=4,threads=1
>>>
>>> From comments we can see:
>>>
>>> * If possible cpus > present cpus here (e.g. some possible
>>> * cpus will be added by cpu-hotplug later), for possible but
>>> * not present cpus, early_cpu_to_node will return NUMA_NO_NODE,
>>> * and we just map them to online nodes in round-robin way.
>>> * Once hotplugged, new correct mapping will be built for them.
>>>
>>> This means even with this patch, cpu_to_node() can return a "valid"
>>> node rather than NUMA_NO_NODE, but this round-robin node is still an
>>> incorrect node.
>> The round-robin node is not standard, may it is copied from x86, I do
>> not know how to use it however. At least SRAT tables provides numa
>> information only that there is not logical cpu allocated in SRAT table
>> parsing. How about something like this?
> This looks better, but maybe Jianmin has a best solution?
>
>>
>> diff --git a/arch/loongarch/kernel/acpi.c b/arch/loongarch/kernel/acpi.c
>> index f1a74b80f22c..bb9fdd318998 100644
>> --- a/arch/loongarch/kernel/acpi.c
>> +++ b/arch/loongarch/kernel/acpi.c
>> @@ -310,6 +310,12 @@ static int __ref acpi_map_cpu2node(acpi_handle
>> handle, int cpu, int physid)
>> int nid;
>>
>> nid = acpi_get_node(handle);
>> + /*
>> + * Fall back to srat numa node information if _PXM is not provided
> The comments may be wrong? I think SRAT node information is equal to _PXM.
"_PXM" information does not belong to SRAT table, it is in DSDT CPU
device table.
For numa system "_PXM" information is required, however for uma system
"_PXM" information is not required since there is only one memory node.
X86 linux uses SRAT table for present cpus and _PXM information in cpu
device for hot-added cpus. For uma system, _PXM is absent and rr method
is used for online nodes, its value is correct still since there is only
one memory node.
Regards
Bibo Mao
>> + */
>> + if (nid != NUMA_NO_NODE)
>> + nid = __cpuid_to_node[physid];
>> +
>> if (nid != NUMA_NO_NODE) {
> Maybe this condition can be removed now?
>
> Huacai
>
>> set_cpuid_to_node(physid, nid);
>> node_set(nid, numa_nodes_parsed);
>>
>> Regards
>> Bibo Mao
>>>
>>> Huacai
>>>
>>>>
>>>> Regards
>>>> Bibo Mao
>>>>>
>>>>> Huacai
>>>>>>
>>>>>> Regards
>>>>>> Bibo Mao
>>>>>>
>>>>>>
>>>>>>> set_cpuid_to_node(physid, nid);
>>>>>>> node_set(nid, numa_nodes_parsed);
>>>>>>> set_cpu_numa_node(cpu, nid);
>>>>>>>
>>>>>>> Huacai
>>>>>>>
>>>>>>>>
>>>>>>>> if (physid < 0)
>>>>>>>> return NUMA_NO_NODE;
>>>>>>>>
>>>>>>>> return __cpuid_to_node[physid];
>>>>>>>> }
>>>>>>>>
>>>>>>>> Regards
>>>>>>>> Bibo Mao
>>>>>>>>>
>>>>>>>>> Huacai
>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> Here static array __cpu_to_node and api set_early_cpu_to_node()
>>>>>>>>>> is added, so that early_cpu_to_node is consistent with function
>>>>>>>>>> cpu_to_node() for hot-added cpu.
>>>>>>>>>>
>>>>>>>>>> Signed-off-by: Bibo Mao <maobibo@...ngson.cn>
>>>>>>>>>> ---
>>>>>>>>>> arch/loongarch/include/asm/numa.h | 2 ++
>>>>>>>>>> arch/loongarch/kernel/numa.c | 10 +++++++++-
>>>>>>>>>> arch/loongarch/kernel/smp.c | 1 +
>>>>>>>>>> 3 files changed, 12 insertions(+), 1 deletion(-)
>>>>>>>>>>
>>>>>>>>>> diff --git a/arch/loongarch/include/asm/numa.h b/arch/loongarch/include/asm/numa.h
>>>>>>>>>> index b5f9de9f102e..e8e6fcfb006a 100644
>>>>>>>>>> --- a/arch/loongarch/include/asm/numa.h
>>>>>>>>>> +++ b/arch/loongarch/include/asm/numa.h
>>>>>>>>>> @@ -50,6 +50,7 @@ static inline void set_cpuid_to_node(int cpuid, s16 node)
>>>>>>>>>> }
>>>>>>>>>>
>>>>>>>>>> extern int early_cpu_to_node(int cpu);
>>>>>>>>>> +extern void set_early_cpu_to_node(int cpu, s16 node);
>>>>>>>>>>
>>>>>>>>>> #else
>>>>>>>>>>
>>>>>>>>>> @@ -57,6 +58,7 @@ static inline void early_numa_add_cpu(int cpuid, s16 node) { }
>>>>>>>>>> static inline void numa_add_cpu(unsigned int cpu) { }
>>>>>>>>>> static inline void numa_remove_cpu(unsigned int cpu) { }
>>>>>>>>>> static inline void set_cpuid_to_node(int cpuid, s16 node) { }
>>>>>>>>>> +static inline void set_early_cpu_to_node(int cpu, s16 node) { }
>>>>>>>>>>
>>>>>>>>>> static inline int early_cpu_to_node(int cpu)
>>>>>>>>>> {
>>>>>>>>>> diff --git a/arch/loongarch/kernel/numa.c b/arch/loongarch/kernel/numa.c
>>>>>>>>>> index 84fe7f854820..62508aace644 100644
>>>>>>>>>> --- a/arch/loongarch/kernel/numa.c
>>>>>>>>>> +++ b/arch/loongarch/kernel/numa.c
>>>>>>>>>> @@ -34,6 +34,9 @@ static struct numa_meminfo numa_meminfo;
>>>>>>>>>> cpumask_t cpus_on_node[MAX_NUMNODES];
>>>>>>>>>> cpumask_t phys_cpus_on_node[MAX_NUMNODES];
>>>>>>>>>> EXPORT_SYMBOL(cpus_on_node);
>>>>>>>>>> +static s16 __cpu_to_node[NR_CPUS] = {
>>>>>>>>>> + [0 ... CONFIG_NR_CPUS - 1] = NUMA_NO_NODE
>>>>>>>>>> +};
>>>>>>>>>>
>>>>>>>>>> /*
>>>>>>>>>> * apicid, cpu, node mappings
>>>>>>>>>> @@ -117,11 +120,16 @@ int early_cpu_to_node(int cpu)
>>>>>>>>>> int physid = cpu_logical_map(cpu);
>>>>>>>>>>
>>>>>>>>>> if (physid < 0)
>>>>>>>>>> - return NUMA_NO_NODE;
>>>>>>>>>> + return __cpu_to_node[cpu];
>>>>>>>>>>
>>>>>>>>>> return __cpuid_to_node[physid];
>>>>>>>>>> }
>>>>>>>>>>
>>>>>>>>>> +void set_early_cpu_to_node(int cpu, s16 node)
>>>>>>>>>> +{
>>>>>>>>>> + __cpu_to_node[cpu] = node;
>>>>>>>>>> +}
>>>>>>>>>> +
>>>>>>>>>> void __init early_numa_add_cpu(int cpuid, s16 node)
>>>>>>>>>> {
>>>>>>>>>> int cpu = __cpu_number_map[cpuid];
>>>>>>>>>> diff --git a/arch/loongarch/kernel/smp.c b/arch/loongarch/kernel/smp.c
>>>>>>>>>> index 9afc2d8b3414..998668be858c 100644
>>>>>>>>>> --- a/arch/loongarch/kernel/smp.c
>>>>>>>>>> +++ b/arch/loongarch/kernel/smp.c
>>>>>>>>>> @@ -512,6 +512,7 @@ void __init smp_prepare_boot_cpu(void)
>>>>>>>>>> set_cpu_numa_node(cpu, node);
>>>>>>>>>> else {
>>>>>>>>>> set_cpu_numa_node(cpu, rr_node);
>>>>>>>>>> + set_early_cpu_to_node(cpu, rr_node);
>>>>>>>>>> rr_node = next_node_in(rr_node, node_online_map);
>>>>>>>>>> }
>>>>>>>>>> }
>>>>>>>>>>
>>>>>>>>>> base-commit: 6485cf5ea253d40d507cd71253c9568c5470cd27
>>>>>>>>>> --
>>>>>>>>>> 2.39.3
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>
>>>>>>
>>>>
>>>>
>>
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