Root/lib/cpu_rmap.c

1/*
2 * cpu_rmap.c: CPU affinity reverse-map support
3 * Copyright 2011 Solarflare Communications Inc.
4 *
5 * This program is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 as published
7 * by the Free Software Foundation, incorporated herein by reference.
8 */
9
10#include <linux/cpu_rmap.h>
11#include <linux/interrupt.h>
12#include <linux/export.h>
13
14/*
15 * These functions maintain a mapping from CPUs to some ordered set of
16 * objects with CPU affinities. This can be seen as a reverse-map of
17 * CPU affinity. However, we do not assume that the object affinities
18 * cover all CPUs in the system. For those CPUs not directly covered
19 * by object affinities, we attempt to find a nearest object based on
20 * CPU topology.
21 */
22
23/**
24 * alloc_cpu_rmap - allocate CPU affinity reverse-map
25 * @size: Number of objects to be mapped
26 * @flags: Allocation flags e.g. %GFP_KERNEL
27 */
28struct cpu_rmap *alloc_cpu_rmap(unsigned int size, gfp_t flags)
29{
30    struct cpu_rmap *rmap;
31    unsigned int cpu;
32    size_t obj_offset;
33
34    /* This is a silly number of objects, and we use u16 indices. */
35    if (size > 0xffff)
36        return NULL;
37
38    /* Offset of object pointer array from base structure */
39    obj_offset = ALIGN(offsetof(struct cpu_rmap, near[nr_cpu_ids]),
40               sizeof(void *));
41
42    rmap = kzalloc(obj_offset + size * sizeof(rmap->obj[0]), flags);
43    if (!rmap)
44        return NULL;
45
46    kref_init(&rmap->refcount);
47    rmap->obj = (void **)((char *)rmap + obj_offset);
48
49    /* Initially assign CPUs to objects on a rota, since we have
50     * no idea where the objects are. Use infinite distance, so
51     * any object with known distance is preferable. Include the
52     * CPUs that are not present/online, since we definitely want
53     * any newly-hotplugged CPUs to have some object assigned.
54     */
55    for_each_possible_cpu(cpu) {
56        rmap->near[cpu].index = cpu % size;
57        rmap->near[cpu].dist = CPU_RMAP_DIST_INF;
58    }
59
60    rmap->size = size;
61    return rmap;
62}
63EXPORT_SYMBOL(alloc_cpu_rmap);
64
65/**
66 * cpu_rmap_release - internal reclaiming helper called from kref_put
67 * @ref: kref to struct cpu_rmap
68 */
69static void cpu_rmap_release(struct kref *ref)
70{
71    struct cpu_rmap *rmap = container_of(ref, struct cpu_rmap, refcount);
72    kfree(rmap);
73}
74
75/**
76 * cpu_rmap_get - internal helper to get new ref on a cpu_rmap
77 * @rmap: reverse-map allocated with alloc_cpu_rmap()
78 */
79static inline void cpu_rmap_get(struct cpu_rmap *rmap)
80{
81    kref_get(&rmap->refcount);
82}
83
84/**
85 * cpu_rmap_put - release ref on a cpu_rmap
86 * @rmap: reverse-map allocated with alloc_cpu_rmap()
87 */
88int cpu_rmap_put(struct cpu_rmap *rmap)
89{
90    return kref_put(&rmap->refcount, cpu_rmap_release);
91}
92EXPORT_SYMBOL(cpu_rmap_put);
93
94/* Reevaluate nearest object for given CPU, comparing with the given
95 * neighbours at the given distance.
96 */
97static bool cpu_rmap_copy_neigh(struct cpu_rmap *rmap, unsigned int cpu,
98                const struct cpumask *mask, u16 dist)
99{
100    int neigh;
101
102    for_each_cpu(neigh, mask) {
103        if (rmap->near[cpu].dist > dist &&
104            rmap->near[neigh].dist <= dist) {
105            rmap->near[cpu].index = rmap->near[neigh].index;
106            rmap->near[cpu].dist = dist;
107            return true;
108        }
109    }
110    return false;
111}
112
113#ifdef DEBUG
114static void debug_print_rmap(const struct cpu_rmap *rmap, const char *prefix)
115{
116    unsigned index;
117    unsigned int cpu;
118
119    pr_info("cpu_rmap %p, %s:\n", rmap, prefix);
120
121    for_each_possible_cpu(cpu) {
122        index = rmap->near[cpu].index;
123        pr_info("cpu %d -> obj %u (distance %u)\n",
124            cpu, index, rmap->near[cpu].dist);
125    }
126}
127#else
128static inline void
129debug_print_rmap(const struct cpu_rmap *rmap, const char *prefix)
130{
131}
132#endif
133
134/**
135 * cpu_rmap_add - add object to a rmap
136 * @rmap: CPU rmap allocated with alloc_cpu_rmap()
137 * @obj: Object to add to rmap
138 *
139 * Return index of object.
140 */
141int cpu_rmap_add(struct cpu_rmap *rmap, void *obj)
142{
143    u16 index;
144
145    BUG_ON(rmap->used >= rmap->size);
146    index = rmap->used++;
147    rmap->obj[index] = obj;
148    return index;
149}
150EXPORT_SYMBOL(cpu_rmap_add);
151
152/**
153 * cpu_rmap_update - update CPU rmap following a change of object affinity
154 * @rmap: CPU rmap to update
155 * @index: Index of object whose affinity changed
156 * @affinity: New CPU affinity of object
157 */
158int cpu_rmap_update(struct cpu_rmap *rmap, u16 index,
159            const struct cpumask *affinity)
160{
161    cpumask_var_t update_mask;
162    unsigned int cpu;
163
164    if (unlikely(!zalloc_cpumask_var(&update_mask, GFP_KERNEL)))
165        return -ENOMEM;
166
167    /* Invalidate distance for all CPUs for which this used to be
168     * the nearest object. Mark those CPUs for update.
169     */
170    for_each_online_cpu(cpu) {
171        if (rmap->near[cpu].index == index) {
172            rmap->near[cpu].dist = CPU_RMAP_DIST_INF;
173            cpumask_set_cpu(cpu, update_mask);
174        }
175    }
176
177    debug_print_rmap(rmap, "after invalidating old distances");
178
179    /* Set distance to 0 for all CPUs in the new affinity mask.
180     * Mark all CPUs within their NUMA nodes for update.
181     */
182    for_each_cpu(cpu, affinity) {
183        rmap->near[cpu].index = index;
184        rmap->near[cpu].dist = 0;
185        cpumask_or(update_mask, update_mask,
186               cpumask_of_node(cpu_to_node(cpu)));
187    }
188
189    debug_print_rmap(rmap, "after updating neighbours");
190
191    /* Update distances based on topology */
192    for_each_cpu(cpu, update_mask) {
193        if (cpu_rmap_copy_neigh(rmap, cpu,
194                    topology_thread_cpumask(cpu), 1))
195            continue;
196        if (cpu_rmap_copy_neigh(rmap, cpu,
197                    topology_core_cpumask(cpu), 2))
198            continue;
199        if (cpu_rmap_copy_neigh(rmap, cpu,
200                    cpumask_of_node(cpu_to_node(cpu)), 3))
201            continue;
202        /* We could continue into NUMA node distances, but for now
203         * we give up.
204         */
205    }
206
207    debug_print_rmap(rmap, "after copying neighbours");
208
209    free_cpumask_var(update_mask);
210    return 0;
211}
212EXPORT_SYMBOL(cpu_rmap_update);
213
214/* Glue between IRQ affinity notifiers and CPU rmaps */
215
216struct irq_glue {
217    struct irq_affinity_notify notify;
218    struct cpu_rmap *rmap;
219    u16 index;
220};
221
222/**
223 * free_irq_cpu_rmap - free a CPU affinity reverse-map used for IRQs
224 * @rmap: Reverse-map allocated with alloc_irq_cpu_map(), or %NULL
225 *
226 * Must be called in process context, before freeing the IRQs.
227 */
228void free_irq_cpu_rmap(struct cpu_rmap *rmap)
229{
230    struct irq_glue *glue;
231    u16 index;
232
233    if (!rmap)
234        return;
235
236    for (index = 0; index < rmap->used; index++) {
237        glue = rmap->obj[index];
238        irq_set_affinity_notifier(glue->notify.irq, NULL);
239    }
240
241    cpu_rmap_put(rmap);
242}
243EXPORT_SYMBOL(free_irq_cpu_rmap);
244
245/**
246 * irq_cpu_rmap_notify - callback for IRQ subsystem when IRQ affinity updated
247 * @notify: struct irq_affinity_notify passed by irq/manage.c
248 * @mask: cpu mask for new SMP affinity
249 *
250 * This is executed in workqueue context.
251 */
252static void
253irq_cpu_rmap_notify(struct irq_affinity_notify *notify, const cpumask_t *mask)
254{
255    struct irq_glue *glue =
256        container_of(notify, struct irq_glue, notify);
257    int rc;
258
259    rc = cpu_rmap_update(glue->rmap, glue->index, mask);
260    if (rc)
261        pr_warning("irq_cpu_rmap_notify: update failed: %d\n", rc);
262}
263
264/**
265 * irq_cpu_rmap_release - reclaiming callback for IRQ subsystem
266 * @ref: kref to struct irq_affinity_notify passed by irq/manage.c
267 */
268static void irq_cpu_rmap_release(struct kref *ref)
269{
270    struct irq_glue *glue =
271        container_of(ref, struct irq_glue, notify.kref);
272
273    cpu_rmap_put(glue->rmap);
274    kfree(glue);
275}
276
277/**
278 * irq_cpu_rmap_add - add an IRQ to a CPU affinity reverse-map
279 * @rmap: The reverse-map
280 * @irq: The IRQ number
281 *
282 * This adds an IRQ affinity notifier that will update the reverse-map
283 * automatically.
284 *
285 * Must be called in process context, after the IRQ is allocated but
286 * before it is bound with request_irq().
287 */
288int irq_cpu_rmap_add(struct cpu_rmap *rmap, int irq)
289{
290    struct irq_glue *glue = kzalloc(sizeof(*glue), GFP_KERNEL);
291    int rc;
292
293    if (!glue)
294        return -ENOMEM;
295    glue->notify.notify = irq_cpu_rmap_notify;
296    glue->notify.release = irq_cpu_rmap_release;
297    glue->rmap = rmap;
298    cpu_rmap_get(rmap);
299    glue->index = cpu_rmap_add(rmap, glue);
300    rc = irq_set_affinity_notifier(irq, &glue->notify);
301    if (rc) {
302        cpu_rmap_put(glue->rmap);
303        kfree(glue);
304    }
305    return rc;
306}
307EXPORT_SYMBOL(irq_cpu_rmap_add);
308

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