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Message-ID: <1840596.ysIY9qmoPP@vostro.rjw.lan>
Date: Fri, 11 Sep 2015 01:10:31 +0200
From: "Rafael J. Wysocki" <rjw@...ysocki.net>
To: Tang Chen <tangchen@...fujitsu.com>
Cc: tj@...nel.org, jiang.liu@...ux.intel.com,
mika.j.penttila@...il.com, mingo@...hat.com,
akpm@...ux-foundation.org, hpa@...or.com, yasu.isimatu@...il.com,
isimatu.yasuaki@...fujitsu.com, kamezawa.hiroyu@...fujitsu.com,
izumi.taku@...fujitsu.com, gongzhaogang@...pur.com,
qiaonuohan@...fujitsu.com, x86@...nel.org,
linux-acpi@...r.kernel.org, linux-kernel@...r.kernel.org,
linux-mm@...ck.org, Gu Zheng <guz.fnst@...fujitsu.com>
Subject: Re: [PATCH v2 4/7] x86, acpi, cpu-hotplug: Enable acpi to register all possible cpus at boot time.
On Thursday, September 10, 2015 12:27:46 PM Tang Chen wrote:
> From: Gu Zheng <guz.fnst@...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.
Can you please avoid using the same (or at least very similar changelog)
for multiple patches in the series? That doesn't help a lot.
> Signed-off-by: Gu Zheng <guz.fnst@...fujitsu.com>
> Signed-off-by: Tang Chen <tangchen@...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 dcb5285..a9c9830 100644
> --- a/arch/x86/kernel/apic/apic.c
> +++ b/arch/x86/kernel/apic/apic.c
> @@ -1977,7 +1977,7 @@ 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,
> @@ -2011,7 +2011,8 @@ int generic_processor_info(int apicid, int version)
> " Processor %d/0x%x ignored.\n",
> thiscpu, apicid);
>
> - disabled_cpus++;
> + if (enabled)
> + disabled_cpus++;
This doesn't look particularly clean to me to be honest.
> return -ENODEV;
> }
>
> @@ -2028,7 +2029,8 @@ 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++;
Likewise and so on.
Maybe call it "enabled_only"?
> return -ENODEV;
> }
>
> @@ -2039,11 +2041,14 @@ 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
> @@ -2071,7 +2076,8 @@ 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;
>
> @@ -2084,11 +2090,17 @@ 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();
>
Thanks,
Rafael
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