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Message-ID: <CAAhV-H4esrPeWAM1ExA2xAsUQ_Aitncro-i31e4wJO5OOVcwEQ@mail.gmail.com>
Date: Mon, 14 Oct 2024 17:29:08 +0800
From: Huacai Chen <chenhuacai@...nel.org>
To: maobibo <maobibo@...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 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?
>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.
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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