dm round robin: revert "use percpu 'repeat_count' and 'current_path'"
The sloppy nature of lockless access to percpu pointers (s->current_path) in rr_select_path(), from multiple threads, is causing some paths to used more than others -- which results in less IO performance being observed. Revert these upstream commits to restore truly symmetric round-robin IO submission in DM multipath:b0b477c
dm round robin: use percpu 'repeat_count' and 'current_path'802934b
dm round robin: do not use this_cpu_ptr() without having preemption disabled There is no benefit to all this complexity if repeat_count = 1 (which is the recommended default). Cc: stable@vger.kernel.org # 4.6+ Signed-off-by: Mike Snitzer <snitzer@redhat.com>
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6085831883
commit
37a098e9d1
1 changed files with 14 additions and 53 deletions
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@ -17,8 +17,8 @@
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#include <linux/module.h>
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#include <linux/module.h>
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#define DM_MSG_PREFIX "multipath round-robin"
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#define DM_MSG_PREFIX "multipath round-robin"
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#define RR_MIN_IO 1000
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#define RR_MIN_IO 1
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#define RR_VERSION "1.1.0"
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#define RR_VERSION "1.2.0"
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/*-----------------------------------------------------------------
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/*-----------------------------------------------------------------
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* Path-handling code, paths are held in lists
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* Path-handling code, paths are held in lists
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@ -47,44 +47,19 @@ struct selector {
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struct list_head valid_paths;
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struct list_head valid_paths;
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struct list_head invalid_paths;
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struct list_head invalid_paths;
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spinlock_t lock;
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spinlock_t lock;
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struct dm_path * __percpu *current_path;
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struct percpu_counter repeat_count;
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};
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};
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static void set_percpu_current_path(struct selector *s, struct dm_path *path)
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{
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int cpu;
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for_each_possible_cpu(cpu)
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*per_cpu_ptr(s->current_path, cpu) = path;
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}
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static struct selector *alloc_selector(void)
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static struct selector *alloc_selector(void)
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{
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{
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struct selector *s = kmalloc(sizeof(*s), GFP_KERNEL);
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struct selector *s = kmalloc(sizeof(*s), GFP_KERNEL);
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if (!s)
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if (s) {
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return NULL;
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INIT_LIST_HEAD(&s->valid_paths);
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INIT_LIST_HEAD(&s->invalid_paths);
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INIT_LIST_HEAD(&s->valid_paths);
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spin_lock_init(&s->lock);
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INIT_LIST_HEAD(&s->invalid_paths);
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}
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spin_lock_init(&s->lock);
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s->current_path = alloc_percpu(struct dm_path *);
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if (!s->current_path)
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goto out_current_path;
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set_percpu_current_path(s, NULL);
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if (percpu_counter_init(&s->repeat_count, 0, GFP_KERNEL))
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goto out_repeat_count;
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return s;
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return s;
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out_repeat_count:
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free_percpu(s->current_path);
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out_current_path:
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kfree(s);
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return NULL;;
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}
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}
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static int rr_create(struct path_selector *ps, unsigned argc, char **argv)
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static int rr_create(struct path_selector *ps, unsigned argc, char **argv)
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@ -105,8 +80,6 @@ static void rr_destroy(struct path_selector *ps)
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free_paths(&s->valid_paths);
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free_paths(&s->valid_paths);
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free_paths(&s->invalid_paths);
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free_paths(&s->invalid_paths);
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free_percpu(s->current_path);
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percpu_counter_destroy(&s->repeat_count);
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kfree(s);
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kfree(s);
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ps->context = NULL;
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ps->context = NULL;
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}
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}
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@ -157,6 +130,11 @@ static int rr_add_path(struct path_selector *ps, struct dm_path *path,
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return -EINVAL;
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return -EINVAL;
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}
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}
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if (repeat_count > 1) {
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DMWARN_LIMIT("repeat_count > 1 is deprecated, using 1 instead");
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repeat_count = 1;
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}
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/* allocate the path */
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/* allocate the path */
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pi = kmalloc(sizeof(*pi), GFP_KERNEL);
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pi = kmalloc(sizeof(*pi), GFP_KERNEL);
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if (!pi) {
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if (!pi) {
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@ -183,9 +161,6 @@ static void rr_fail_path(struct path_selector *ps, struct dm_path *p)
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struct path_info *pi = p->pscontext;
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struct path_info *pi = p->pscontext;
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spin_lock_irqsave(&s->lock, flags);
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spin_lock_irqsave(&s->lock, flags);
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if (p == *this_cpu_ptr(s->current_path))
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set_percpu_current_path(s, NULL);
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list_move(&pi->list, &s->invalid_paths);
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list_move(&pi->list, &s->invalid_paths);
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spin_unlock_irqrestore(&s->lock, flags);
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spin_unlock_irqrestore(&s->lock, flags);
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}
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}
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@ -208,29 +183,15 @@ static struct dm_path *rr_select_path(struct path_selector *ps, size_t nr_bytes)
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unsigned long flags;
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unsigned long flags;
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struct selector *s = ps->context;
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struct selector *s = ps->context;
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struct path_info *pi = NULL;
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struct path_info *pi = NULL;
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struct dm_path *current_path = NULL;
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local_irq_save(flags);
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spin_lock_irqsave(&s->lock, flags);
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current_path = *this_cpu_ptr(s->current_path);
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if (current_path) {
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percpu_counter_dec(&s->repeat_count);
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if (percpu_counter_read_positive(&s->repeat_count) > 0) {
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local_irq_restore(flags);
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return current_path;
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}
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}
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spin_lock(&s->lock);
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if (!list_empty(&s->valid_paths)) {
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if (!list_empty(&s->valid_paths)) {
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pi = list_entry(s->valid_paths.next, struct path_info, list);
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pi = list_entry(s->valid_paths.next, struct path_info, list);
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list_move_tail(&pi->list, &s->valid_paths);
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list_move_tail(&pi->list, &s->valid_paths);
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percpu_counter_set(&s->repeat_count, pi->repeat_count);
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set_percpu_current_path(s, pi->path);
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current_path = pi->path;
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}
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}
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spin_unlock_irqrestore(&s->lock, flags);
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spin_unlock_irqrestore(&s->lock, flags);
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return current_path;
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return pi ? pi->path : NULL;
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}
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}
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static struct path_selector_type rr_ps = {
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static struct path_selector_type rr_ps = {
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