lib/cpumask.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 #include <linux/slab.h>
   3 #include <linux/kernel.h>
   4 #include <linux/bitops.h>
   5 #include <linux/cpumask.h>
   6 #include <linux/export.h>
   7 #include <linux/memblock.h>
   8 #include <linux/numa.h>
   9
  10 /**
  11  * cpumask_next_wrap - helper to implement for_each_cpu_wrap
  12  * @n: the cpu prior to the place to search
  13  * @mask: the cpumask pointer
  14  * @start: the start point of the iteration
  15  * @wrap: assume @n crossing @start terminates the iteration
  16  *
  17  * Return: >= nr_cpu_ids on completion
  18  *
  19  * Note: the @wrap argument is required for the start condition when
  20  * we cannot assume @start is set in @mask.
  21  */
  22 unsigned int cpumask_next_wrap(int n, const struct cpumask *mask, int start, bool wrap)
  23 {
  24         unsigned int next;
  25
  26 again:
  27         next = cpumask_next(n, mask);
  28
  29         if (wrap && n < start && next >= start) {
  30                 return nr_cpumask_bits;
  31
  32         } else if (next >= nr_cpumask_bits) {
  33                 wrap = true;
  34                 n = -1;
  35                 goto again;
  36         }
  37
  38         return next;
  39 }
  40 EXPORT_SYMBOL(cpumask_next_wrap);
  41
  42 /* These are not inline because of header tangles. */
  43 #ifdef CONFIG_CPUMASK_OFFSTACK
  44 /**
  45  * alloc_cpumask_var_node - allocate a struct cpumask on a given node
  46  * @mask: pointer to cpumask_var_t where the cpumask is returned
  47  * @flags: GFP_ flags
  48  * @node: memory node from which to allocate or %NUMA_NO_NODE
  49  *
  50  * Only defined when CONFIG_CPUMASK_OFFSTACK=y, otherwise is
  51  * a nop returning a constant 1 (in <linux/cpumask.h>).
  52  *
  53  * Return: TRUE if memory allocation succeeded, FALSE otherwise.
  54  *
  55  * In addition, mask will be NULL if this fails.  Note that gcc is
  56  * usually smart enough to know that mask can never be NULL if
  57  * CONFIG_CPUMASK_OFFSTACK=n, so does code elimination in that case
  58  * too.
  59  */
  60 bool alloc_cpumask_var_node(cpumask_var_t *mask, gfp_t flags, int node)
  61 {
  62         *mask = kmalloc_node(cpumask_size(), flags, node);
  63
  64 #ifdef CONFIG_DEBUG_PER_CPU_MAPS
  65         if (!*mask) {
  66                 printk(KERN_ERR "=> alloc_cpumask_var: failed!\n");
  67                 dump_stack();
  68         }
  69 #endif
  70
  71         return *mask != NULL;
  72 }
  73 EXPORT_SYMBOL(alloc_cpumask_var_node);
  74
  75 /**
  76  * alloc_bootmem_cpumask_var - allocate a struct cpumask from the bootmem arena.
  77  * @mask: pointer to cpumask_var_t where the cpumask is returned
  78  *
  79  * Only defined when CONFIG_CPUMASK_OFFSTACK=y, otherwise is
  80  * a nop (in <linux/cpumask.h>).
  81  * Either returns an allocated (zero-filled) cpumask, or causes the
  82  * system to panic.
  83  */
  84 void __init alloc_bootmem_cpumask_var(cpumask_var_t *mask)
  85 {
  86         *mask = memblock_alloc(cpumask_size(), SMP_CACHE_BYTES);
  87         if (!*mask)
  88                 panic("%s: Failed to allocate %u bytes\n", __func__,
  89                       cpumask_size());
  90 }
  91
  92 /**
  93  * free_cpumask_var - frees memory allocated for a struct cpumask.
  94  * @mask: cpumask to free
  95  *
  96  * This is safe on a NULL mask.
  97  */
  98 void free_cpumask_var(cpumask_var_t mask)
  99 {
 100         kfree(mask);
 101 }
 102 EXPORT_SYMBOL(free_cpumask_var);
 103
 104 /**
 105  * free_bootmem_cpumask_var - frees result of alloc_bootmem_cpumask_var
 106  * @mask: cpumask to free
 107  */
 108 void __init free_bootmem_cpumask_var(cpumask_var_t mask)
 109 {
 110         memblock_free(mask, cpumask_size());
 111 }
 112 #endif
 113
 114 /**
 115  * cpumask_local_spread - select the i'th cpu based on NUMA distances
 116  * @i: index number
 117  * @node: local numa_node
 118  *
 119  * Return: online CPU according to a numa aware policy; local cpus are returned
 120  * first, followed by non-local ones, then it wraps around.
 121  *
 122  * For those who wants to enumerate all CPUs based on their NUMA distances,
 123  * i.e. call this function in a loop, like:
 124  *
 125  * for (i = 0; i < num_online_cpus(); i++) {
 126  *      cpu = cpumask_local_spread(i, node);
 127  *      do_something(cpu);
 128  * }
 129  *
 130  * There's a better alternative based on for_each()-like iterators:
 131  *
 132  *      for_each_numa_hop_mask(mask, node) {
 133  *              for_each_cpu_andnot(cpu, mask, prev)
 134  *                      do_something(cpu);
 135  *              prev = mask;
 136  *      }
 137  *
 138  * It's simpler and more verbose than above. Complexity of iterator-based
 139  * enumeration is O(sched_domains_numa_levels * nr_cpu_ids), while
 140  * cpumask_local_spread() when called for each cpu is
 141  * O(sched_domains_numa_levels * nr_cpu_ids * log(nr_cpu_ids)).
 142  */
 143 unsigned int cpumask_local_spread(unsigned int i, int node)
 144 {
 145         unsigned int cpu;
 146
 147         /* Wrap: we always want a cpu. */
 148         i %= num_online_cpus();
 149
 150         cpu = sched_numa_find_nth_cpu(cpu_online_mask, i, node);
 151
 152         WARN_ON(cpu >= nr_cpu_ids);
 153         return cpu;
 154 }
 155 EXPORT_SYMBOL(cpumask_local_spread);
 156
 157 static DEFINE_PER_CPU(int, distribute_cpu_mask_prev);
 158
 159 /**
 160  * cpumask_any_and_distribute - Return an arbitrary cpu within src1p & src2p.
 161  * @src1p: first &cpumask for intersection
 162  * @src2p: second &cpumask for intersection
 163  *
 164  * Iterated calls using the same srcp1 and srcp2 will be distributed within
 165  * their intersection.
 166  *
 167  * Return: >= nr_cpu_ids if the intersection is empty.
 168  */
 169 unsigned int cpumask_any_and_distribute(const struct cpumask *src1p,
 170                                const struct cpumask *src2p)
 171 {
 172         unsigned int next, prev;
 173
 174         /* NOTE: our first selection will skip 0. */
 175         prev = __this_cpu_read(distribute_cpu_mask_prev);
 176
 177         next = find_next_and_bit_wrap(cpumask_bits(src1p), cpumask_bits(src2p),
 178                                         nr_cpumask_bits, prev + 1);
 179         if (next < nr_cpu_ids)
 180                 __this_cpu_write(distribute_cpu_mask_prev, next);
 181
 182         return next;
 183 }
 184 EXPORT_SYMBOL(cpumask_any_and_distribute);
 185
 186 /**
 187  * cpumask_any_distribute - Return an arbitrary cpu from srcp
 188  * @srcp: &cpumask for selection
 189  *
 190  * Return: >= nr_cpu_ids if the intersection is empty.
 191  */
 192 unsigned int cpumask_any_distribute(const struct cpumask *srcp)
 193 {
 194         unsigned int next, prev;
 195
 196         /* NOTE: our first selection will skip 0. */
 197         prev = __this_cpu_read(distribute_cpu_mask_prev);
 198         next = find_next_bit_wrap(cpumask_bits(srcp), nr_cpumask_bits, prev + 1);
 199         if (next < nr_cpu_ids)
 200                 __this_cpu_write(distribute_cpu_mask_prev, next);
 201
 202         return next;
 203 }
 204 EXPORT_SYMBOL(cpumask_any_distribute);