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raid5: only wakeup necessary threads
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If there are not enough stripes to handle, we'd better not always
queue all available work_structs. If one worker can only handle small
or even none stripes, it will impact request merge and create lock
contention.

With this patch, the number of work_struct running will depend on
pending stripes number. Note: some statistics info used in the patch
are accessed without locking protection. This should doesn't matter,
we just try best to avoid queue unnecessary work_struct.

Signed-off-by: Shaohua Li <shli@fusionio.com>
Signed-off-by: NeilBrown <neilb@suse.de>
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Shaohua Li authored and NeilBrown committed Sep 2, 2013
1 parent 4d77e3b commit bfc90cb
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Showing 2 changed files with 38 additions and 6 deletions.
41 changes: 35 additions & 6 deletions drivers/md/raid5.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -77,6 +77,7 @@ static struct workqueue_struct *raid5_wq;
#define BYPASS_THRESHOLD 1
#define NR_HASH (PAGE_SIZE / sizeof(struct hlist_head))
#define HASH_MASK (NR_HASH - 1)
#define MAX_STRIPE_BATCH 8

static inline struct hlist_head *stripe_hash(struct r5conf *conf, sector_t sect)
{
Expand Down Expand Up @@ -209,6 +210,7 @@ static void raid5_wakeup_stripe_thread(struct stripe_head *sh)
{
struct r5conf *conf = sh->raid_conf;
struct r5worker_group *group;
int thread_cnt;
int i, cpu = sh->cpu;

if (!cpu_online(cpu)) {
Expand All @@ -220,6 +222,8 @@ static void raid5_wakeup_stripe_thread(struct stripe_head *sh)
struct r5worker_group *group;
group = conf->worker_groups + cpu_to_group(cpu);
list_add_tail(&sh->lru, &group->handle_list);
group->stripes_cnt++;
sh->group = group;
}

if (conf->worker_cnt_per_group == 0) {
Expand All @@ -229,8 +233,20 @@ static void raid5_wakeup_stripe_thread(struct stripe_head *sh)

group = conf->worker_groups + cpu_to_group(sh->cpu);

for (i = 0; i < conf->worker_cnt_per_group; i++)
queue_work_on(sh->cpu, raid5_wq, &group->workers[i].work);
group->workers[0].working = true;
/* at least one worker should run to avoid race */
queue_work_on(sh->cpu, raid5_wq, &group->workers[0].work);

thread_cnt = group->stripes_cnt / MAX_STRIPE_BATCH - 1;
/* wakeup more workers */
for (i = 1; i < conf->worker_cnt_per_group && thread_cnt > 0; i++) {
if (group->workers[i].working == false) {
group->workers[i].working = true;
queue_work_on(sh->cpu, raid5_wq,
&group->workers[i].work);
thread_cnt--;
}
}
}

static void do_release_stripe(struct r5conf *conf, struct stripe_head *sh)
Expand Down Expand Up @@ -589,6 +605,10 @@ get_active_stripe(struct r5conf *conf, sector_t sector,
!test_bit(STRIPE_EXPANDING, &sh->state))
BUG();
list_del_init(&sh->lru);
if (sh->group) {
sh->group->stripes_cnt--;
sh->group = NULL;
}
}
}
} while (sh == NULL);
Expand Down Expand Up @@ -4153,15 +4173,18 @@ static struct stripe_head *__get_priority_stripe(struct r5conf *conf, int group)
{
struct stripe_head *sh = NULL, *tmp;
struct list_head *handle_list = NULL;
struct r5worker_group *wg = NULL;

if (conf->worker_cnt_per_group == 0) {
handle_list = &conf->handle_list;
} else if (group != ANY_GROUP) {
handle_list = &conf->worker_groups[group].handle_list;
wg = &conf->worker_groups[group];
} else {
int i;
for (i = 0; i < conf->group_cnt; i++) {
handle_list = &conf->worker_groups[i].handle_list;
wg = &conf->worker_groups[i];
if (!list_empty(handle_list))
break;
}
Expand Down Expand Up @@ -4208,11 +4231,16 @@ static struct stripe_head *__get_priority_stripe(struct r5conf *conf, int group)
if (conf->bypass_count < 0)
conf->bypass_count = 0;
}
wg = NULL;
}

if (!sh)
return NULL;

if (wg) {
wg->stripes_cnt--;
sh->group = NULL;
}
list_del_init(&sh->lru);
atomic_inc(&sh->count);
BUG_ON(atomic_read(&sh->count) != 1);
Expand Down Expand Up @@ -4919,8 +4947,8 @@ static int retry_aligned_read(struct r5conf *conf, struct bio *raid_bio)
return handled;
}

#define MAX_STRIPE_BATCH 8
static int handle_active_stripes(struct r5conf *conf, int group)
static int handle_active_stripes(struct r5conf *conf, int group,
struct r5worker *worker)
{
struct stripe_head *batch[MAX_STRIPE_BATCH], *sh;
int i, batch_size = 0;
Expand Down Expand Up @@ -4963,7 +4991,8 @@ static void raid5_do_work(struct work_struct *work)

released = release_stripe_list(conf);

batch_size = handle_active_stripes(conf, group_id);
batch_size = handle_active_stripes(conf, group_id, worker);
worker->working = false;
if (!batch_size && !released)
break;
handled += batch_size;
Expand Down Expand Up @@ -5025,7 +5054,7 @@ static void raid5d(struct md_thread *thread)
handled++;
}

batch_size = handle_active_stripes(conf, ANY_GROUP);
batch_size = handle_active_stripes(conf, ANY_GROUP, NULL);
if (!batch_size && !released)
break;
handled += batch_size;
Expand Down
3 changes: 3 additions & 0 deletions drivers/md/raid5.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -213,6 +213,7 @@ struct stripe_head {
enum reconstruct_states reconstruct_state;
spinlock_t stripe_lock;
int cpu;
struct r5worker_group *group;
/**
* struct stripe_operations
* @target - STRIPE_OP_COMPUTE_BLK target
Expand Down Expand Up @@ -369,12 +370,14 @@ struct disk_info {
struct r5worker {
struct work_struct work;
struct r5worker_group *group;
bool working;
};

struct r5worker_group {
struct list_head handle_list;
struct r5conf *conf;
struct r5worker *workers;
int stripes_cnt;
};

struct r5conf {
Expand Down

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