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Subject[PATCH v3 2/5] x86, acpi, cpu-hotplug: Enable acpi to register all possible cpus at boot time.
Date
From: Gu Zheng <guz.fnst@cn.fujitsu.com>

[Problem]

cpuid <-> nodeid mapping is firstly established at boot time. And workqueue caches
the mapping in wq_numa_possible_cpumask in wq_numa_init() at boot time.

When doing node online/offline, cpuid <-> nodeid mapping is established/destroyed,
which means, cpuid <-> nodeid mapping will change if node hotplug happens. But
workqueue does not update wq_numa_possible_cpumask.

So here is the problem:

Assume we have the following cpuid <-> nodeid in the beginning:

Node | CPU
------------------------
node 0 | 0-14, 60-74
node 1 | 15-29, 75-89
node 2 | 30-44, 90-104
node 3 | 45-59, 105-119

and we hot-remove node2 and node3, it becomes:

Node | CPU
------------------------
node 0 | 0-14, 60-74
node 1 | 15-29, 75-89

and we hot-add node4 and node5, it becomes:

Node | CPU
------------------------
node 0 | 0-14, 60-74
node 1 | 15-29, 75-89
node 4 | 30-59
node 5 | 90-119

But in wq_numa_possible_cpumask, cpu30 is still mapped to node2, and the like.

When a pool workqueue is initialized, if its cpumask belongs to a node, its
pool->node will be mapped to that node. And memory used by this workqueue will
also be allocated on that node.

static struct worker_pool *get_unbound_pool(const struct workqueue_attrs *attrs){
...
/* if cpumask is contained inside a NUMA node, we belong to that node */
if (wq_numa_enabled) {
for_each_node(node) {
if (cpumask_subset(pool->attrs->cpumask,
wq_numa_possible_cpumask[node])) {
pool->node = node;
break;
}
}
}

Since wq_numa_possible_cpumask is not updated, it could be mapped to an offline node,
which will lead to memory allocation failure:

SLUB: Unable to allocate memory on node 2 (gfp=0x80d0)
cache: kmalloc-192, object size: 192, buffer size: 192, default order: 1, min order: 0
node 0: slabs: 6172, objs: 259224, free: 245741
node 1: slabs: 3261, objs: 136962, free: 127656

It happens here:

create_worker(struct worker_pool *pool)
|--> worker = alloc_worker(pool->node);

static struct worker *alloc_worker(int node)
{
struct worker *worker;

worker = kzalloc_node(sizeof(*worker), GFP_KERNEL, node); --> Here, useing the wrong node.

......

return worker;
}

[Solution]

There are four mappings in the kernel:
1. nodeid (logical node id) <-> pxm
2. apicid (physical cpu id) <-> nodeid
3. cpuid (logical cpu id) <-> apicid
4. cpuid (logical cpu id) <-> nodeid

1. pxm (proximity domain) is provided by ACPI firmware in SRAT, and nodeid <-> pxm
mapping is setup at boot time. This mapping is persistent, won't change.

2. apicid <-> nodeid mapping is setup using info in 1. The mapping is setup at boot
time and CPU hotadd time, and cleared at CPU hotremove time. This mapping is also
persistent.

3. cpuid <-> apicid mapping is setup at boot time and CPU hotadd time. cpuid is
allocated, lower ids first, and released at CPU hotremove time, reused for other
hotadded CPUs. So this mapping is not persistent.

4. cpuid <-> nodeid mapping is also setup at boot time and CPU hotadd time, and
cleared at CPU hotremove time. As a result of 3, this mapping is not persistent.

To fix this problem, we establish cpuid <-> nodeid mapping for all the possible
cpus at boot time, and make it persistent. And according to init_cpu_to_node(),
cpuid <-> nodeid mapping is based on apicid <-> nodeid mapping and cpuid <-> apicid
mapping. So the key point is obtaining all cpus' apicid.

apicid can be obtained by _MAT (Multiple APIC Table Entry) method or found in
MADT (Multiple APIC Description Table). So we finish the job in the following steps:

1. Enable apic registeration flow to handle both enabled and disabled cpus.
This is done by introducing an extra parameter to generic_processor_info to let the
caller control if disabled cpus are ignored.

2. Introduce a new array storing all possible cpuid <-> apicid mapping. And also modify
the way cpuid is calculated. Establish all possible cpuid <-> apicid mapping when
registering local apic. Store the mapping in this array.

3. Enable _MAT and MADT relative apis to return non-presnet or disabled cpus' apicid.
This is also done by introducing an extra parameter to these apis to let the caller
control if disabled cpus are ignored.

4. Establish all possible cpuid <-> nodeid mapping.
This is done via an additional acpi namespace walk for processors.

This patch finished step 1.

Signed-off-by: Gu Zheng <guz.fnst@cn.fujitsu.com>
Signed-off-by: Tang Chen <tangchen@cn.fujitsu.com>
---
arch/x86/kernel/apic/apic.c | 26 +++++++++++++++++++-------
1 file changed, 19 insertions(+), 7 deletions(-)

diff --git a/arch/x86/kernel/apic/apic.c b/arch/x86/kernel/apic/apic.c
index 2f69e3b..29915cf 100644
--- a/arch/x86/kernel/apic/apic.c
+++ b/arch/x86/kernel/apic/apic.c
@@ -1988,7 +1988,7 @@ void disconnect_bsp_APIC(int virt_wire_setup)
apic_write(APIC_LVT1, value);
}

-int generic_processor_info(int apicid, int version)
+static int __generic_processor_info(int apicid, int version, bool enabled)
{
int cpu, max = nr_cpu_ids;
bool boot_cpu_detected = physid_isset(boot_cpu_physical_apicid,
@@ -2022,7 +2022,8 @@ int generic_processor_info(int apicid, int version)
" Processor %d/0x%x ignored.\n",
thiscpu, apicid);

- disabled_cpus++;
+ if (enabled)
+ disabled_cpus++;
return -ENODEV;
}

@@ -2039,7 +2040,8 @@ int generic_processor_info(int apicid, int version)
" reached. Keeping one slot for boot cpu."
" Processor %d/0x%x ignored.\n", max, thiscpu, apicid);

- disabled_cpus++;
+ if (enabled)
+ disabled_cpus++;
return -ENODEV;
}

@@ -2050,11 +2052,14 @@ int generic_processor_info(int apicid, int version)
"ACPI: NR_CPUS/possible_cpus limit of %i reached."
" Processor %d/0x%x ignored.\n", max, thiscpu, apicid);

- disabled_cpus++;
+ if (enabled)
+ disabled_cpus++;
return -EINVAL;
}

- num_processors++;
+ if (enabled)
+ num_processors++;
+
if (apicid == boot_cpu_physical_apicid) {
/*
* x86_bios_cpu_apicid is required to have processors listed
@@ -2082,7 +2087,8 @@ int generic_processor_info(int apicid, int version)
apic_version[boot_cpu_physical_apicid], cpu, version);
}

- physid_set(apicid, phys_cpu_present_map);
+ if (enabled)
+ physid_set(apicid, phys_cpu_present_map);
if (apicid > max_physical_apicid)
max_physical_apicid = apicid;

@@ -2095,11 +2101,17 @@ int generic_processor_info(int apicid, int version)
apic->x86_32_early_logical_apicid(cpu);
#endif
set_cpu_possible(cpu, true);
- set_cpu_present(cpu, true);
+ if (enabled)
+ set_cpu_present(cpu, true);

return cpu;
}

+int generic_processor_info(int apicid, int version)
+{
+ return __generic_processor_info(apicid, version, true);
+}
+
int hard_smp_processor_id(void)
{
return read_apic_id();
--
1.8.3.1


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