original development tree for Linux kernel GTP module; now long in mainline.
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#include <linux/kernel.h>
#include <linux/threads.h>
#include <linux/module.h>
#include <linux/mm.h>
#include <linux/smp.h>
#include <linux/cpu.h>
#include <linux/blk-mq.h>
#include "blk.h"
#include "blk-mq.h"
static void show_map(unsigned int *map, unsigned int nr)
{
int i;
pr_info("blk-mq: CPU -> queue map\n");
for_each_online_cpu(i)
pr_info(" CPU%2u -> Queue %u\n", i, map[i]);
}
static int cpu_to_queue_index(unsigned int nr_cpus, unsigned int nr_queues,
const int cpu)
{
return cpu / ((nr_cpus + nr_queues - 1) / nr_queues);
}
static int get_first_sibling(unsigned int cpu)
{
unsigned int ret;
ret = cpumask_first(topology_thread_cpumask(cpu));
if (ret < nr_cpu_ids)
return ret;
return cpu;
}
int blk_mq_update_queue_map(unsigned int *map, unsigned int nr_queues)
{
unsigned int i, nr_cpus, nr_uniq_cpus, queue, first_sibling;
cpumask_var_t cpus;
if (!alloc_cpumask_var(&cpus, GFP_ATOMIC))
return 1;
cpumask_clear(cpus);
nr_cpus = nr_uniq_cpus = 0;
for_each_online_cpu(i) {
nr_cpus++;
first_sibling = get_first_sibling(i);
if (!cpumask_test_cpu(first_sibling, cpus))
nr_uniq_cpus++;
cpumask_set_cpu(i, cpus);
}
queue = 0;
for_each_possible_cpu(i) {
if (!cpu_online(i)) {
map[i] = 0;
continue;
}
/*
* Easy case - we have equal or more hardware queues. Or
* there are no thread siblings to take into account. Do
* 1:1 if enough, or sequential mapping if less.
*/
if (nr_queues >= nr_cpus || nr_cpus == nr_uniq_cpus) {
map[i] = cpu_to_queue_index(nr_cpus, nr_queues, queue);
queue++;
continue;
}
/*
* Less then nr_cpus queues, and we have some number of
* threads per cores. Map sibling threads to the same
* queue.
*/
first_sibling = get_first_sibling(i);
if (first_sibling == i) {
map[i] = cpu_to_queue_index(nr_uniq_cpus, nr_queues,
queue);
queue++;
} else
map[i] = map[first_sibling];
}
show_map(map, nr_cpus);
free_cpumask_var(cpus);
return 0;
}
unsigned int *blk_mq_make_queue_map(struct blk_mq_reg *reg)
{
unsigned int *map;
/* If cpus are offline, map them to first hctx */
map = kzalloc_node(sizeof(*map) * num_possible_cpus(), GFP_KERNEL,
reg->numa_node);
if (!map)
return NULL;
if (!blk_mq_update_queue_map(map, reg->nr_hw_queues))
return map;
kfree(map);
return NULL;
}