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The deduplicating sort in sched_init_numa() assumes that the first line in
the distance table contains all unique values in the entire table. I've
been trying to pen what this exactly means for the topology, but it's not
straightforward. For instance, topology.c uses this example:
node 0 1 2 3
0: 10 20 20 30
1: 20 10 20 20
2: 20 20 10 20
3: 30 20 20 10
0 ----- 1
| / |
| / |
| / |
2 ----- 3
Which works out just fine. However, if we swap nodes 0 and 1:
1 ----- 0
| / |
| / |
| / |
2 ----- 3
we get this distance table:
node 0 1 2 3
0: 10 20 20 20
1: 20 10 20 30
2: 20 20 10 20
3: 20 30 20 10
Which breaks the deduplicating sort (non-representative first line). In
this case this would just be a renumbering exercise, but it so happens that
we can have a deduplicating sort that goes through the whole table in O(n²)
at the extra cost of a temporary memory allocation (i.e. any form of set).
The ACPI spec (SLIT) mentions distances are encoded on 8 bits. Following
this, implement the set as a 256-bits bitmap. Should this not be
satisfactory (i.e. we want to support 32-bit values), then we'll have to go
for some other sparse set implementation.
This has the added benefit of letting us allocate just the right amount of
memory for sched_domains_numa_distance[], rather than an arbitrary
(nr_node_ids + 1).
Note: DT binding equivalent (distance-map) decodes distances as 32-bit
values.
Signed-off-by: Valentin Schneider <valentin.schneider@arm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20210122123943.1217-2-valentin.schneider@arm.com
215 lines
5.3 KiB
C
215 lines
5.3 KiB
C
/*
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* include/linux/topology.h
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*
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* Written by: Matthew Dobson, IBM Corporation
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*
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* Copyright (C) 2002, IBM Corp.
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*
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* All rights reserved.
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful, but
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* WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE, GOOD TITLE or
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* NON INFRINGEMENT. See the GNU General Public License for more
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* details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, write to the Free Software
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* Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
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*
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* Send feedback to <colpatch@us.ibm.com>
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*/
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#ifndef _LINUX_TOPOLOGY_H
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#define _LINUX_TOPOLOGY_H
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#include <linux/arch_topology.h>
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#include <linux/cpumask.h>
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#include <linux/bitops.h>
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#include <linux/mmzone.h>
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#include <linux/smp.h>
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#include <linux/percpu.h>
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#include <asm/topology.h>
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#ifndef nr_cpus_node
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#define nr_cpus_node(node) cpumask_weight(cpumask_of_node(node))
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#endif
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#define for_each_node_with_cpus(node) \
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for_each_online_node(node) \
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if (nr_cpus_node(node))
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int arch_update_cpu_topology(void);
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/* Conform to ACPI 2.0 SLIT distance definitions */
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#define LOCAL_DISTANCE 10
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#define REMOTE_DISTANCE 20
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#define DISTANCE_BITS 8
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#ifndef node_distance
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#define node_distance(from,to) ((from) == (to) ? LOCAL_DISTANCE : REMOTE_DISTANCE)
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#endif
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#ifndef RECLAIM_DISTANCE
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/*
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* If the distance between nodes in a system is larger than RECLAIM_DISTANCE
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* (in whatever arch specific measurement units returned by node_distance())
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* and node_reclaim_mode is enabled then the VM will only call node_reclaim()
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* on nodes within this distance.
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*/
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#define RECLAIM_DISTANCE 30
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#endif
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/*
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* The following tunable allows platforms to override the default node
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* reclaim distance (RECLAIM_DISTANCE) if remote memory accesses are
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* sufficiently fast that the default value actually hurts
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* performance.
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*
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* AMD EPYC machines use this because even though the 2-hop distance
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* is 32 (3.2x slower than a local memory access) performance actually
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* *improves* if allowed to reclaim memory and load balance tasks
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* between NUMA nodes 2-hops apart.
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*/
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extern int __read_mostly node_reclaim_distance;
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#ifndef PENALTY_FOR_NODE_WITH_CPUS
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#define PENALTY_FOR_NODE_WITH_CPUS (1)
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#endif
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#ifdef CONFIG_USE_PERCPU_NUMA_NODE_ID
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DECLARE_PER_CPU(int, numa_node);
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#ifndef numa_node_id
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/* Returns the number of the current Node. */
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static inline int numa_node_id(void)
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{
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return raw_cpu_read(numa_node);
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}
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#endif
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#ifndef cpu_to_node
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static inline int cpu_to_node(int cpu)
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{
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return per_cpu(numa_node, cpu);
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}
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#endif
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#ifndef set_numa_node
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static inline void set_numa_node(int node)
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{
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this_cpu_write(numa_node, node);
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}
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#endif
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#ifndef set_cpu_numa_node
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static inline void set_cpu_numa_node(int cpu, int node)
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{
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per_cpu(numa_node, cpu) = node;
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}
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#endif
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#else /* !CONFIG_USE_PERCPU_NUMA_NODE_ID */
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/* Returns the number of the current Node. */
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#ifndef numa_node_id
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static inline int numa_node_id(void)
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{
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return cpu_to_node(raw_smp_processor_id());
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}
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#endif
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#endif /* [!]CONFIG_USE_PERCPU_NUMA_NODE_ID */
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#ifdef CONFIG_HAVE_MEMORYLESS_NODES
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/*
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* N.B., Do NOT reference the '_numa_mem_' per cpu variable directly.
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* It will not be defined when CONFIG_HAVE_MEMORYLESS_NODES is not defined.
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* Use the accessor functions set_numa_mem(), numa_mem_id() and cpu_to_mem().
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*/
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DECLARE_PER_CPU(int, _numa_mem_);
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#ifndef set_numa_mem
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static inline void set_numa_mem(int node)
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{
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this_cpu_write(_numa_mem_, node);
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}
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#endif
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#ifndef numa_mem_id
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/* Returns the number of the nearest Node with memory */
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static inline int numa_mem_id(void)
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{
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return raw_cpu_read(_numa_mem_);
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}
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#endif
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#ifndef cpu_to_mem
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static inline int cpu_to_mem(int cpu)
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{
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return per_cpu(_numa_mem_, cpu);
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}
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#endif
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#ifndef set_cpu_numa_mem
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static inline void set_cpu_numa_mem(int cpu, int node)
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{
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per_cpu(_numa_mem_, cpu) = node;
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}
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#endif
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#else /* !CONFIG_HAVE_MEMORYLESS_NODES */
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#ifndef numa_mem_id
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/* Returns the number of the nearest Node with memory */
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static inline int numa_mem_id(void)
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{
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return numa_node_id();
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}
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#endif
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#ifndef cpu_to_mem
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static inline int cpu_to_mem(int cpu)
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{
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return cpu_to_node(cpu);
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}
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#endif
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#endif /* [!]CONFIG_HAVE_MEMORYLESS_NODES */
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#ifndef topology_physical_package_id
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#define topology_physical_package_id(cpu) ((void)(cpu), -1)
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#endif
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#ifndef topology_die_id
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#define topology_die_id(cpu) ((void)(cpu), -1)
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#endif
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#ifndef topology_core_id
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#define topology_core_id(cpu) ((void)(cpu), 0)
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#endif
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#ifndef topology_sibling_cpumask
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#define topology_sibling_cpumask(cpu) cpumask_of(cpu)
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#endif
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#ifndef topology_core_cpumask
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#define topology_core_cpumask(cpu) cpumask_of(cpu)
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#endif
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#ifndef topology_die_cpumask
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#define topology_die_cpumask(cpu) cpumask_of(cpu)
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#endif
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#if defined(CONFIG_SCHED_SMT) && !defined(cpu_smt_mask)
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static inline const struct cpumask *cpu_smt_mask(int cpu)
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{
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return topology_sibling_cpumask(cpu);
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}
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#endif
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static inline const struct cpumask *cpu_cpu_mask(int cpu)
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{
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return cpumask_of_node(cpu_to_node(cpu));
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}
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#endif /* _LINUX_TOPOLOGY_H */
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