io-threads: single queue/multi-thread model

This patch lets io-threads work with a single queue and multiple
threads work on picking the next request from the queue and process
it.

Whenever the number of pending requests in the queue double, a new
worker thread is spawned.

Workers expire after a (configurable) timeout of inactivity

Signed-off-by: Anand V. Avati <avati@amp.gluster.com>
Signed-off-by: Anand V. Avati <avati@blackhole.gluster.com>
Signed-off-by: Anand V. Avati <avati@dev.gluster.com>

BUG: 583 (filesystem access hangs while deleting large files)
URL: http://bugs.gluster.com/cgi-bin/bugzilla3/show_bug.cgi?id=583

2 files changed, 154 insertions, 956 deletions

diff --git a/xlators/performance/io-threads/src/io-threads.c b/xlators/performance/io-threads/src/io-threads.c
index e99012cc0d6..5339ce9a8c1 100644
--- a/xlators/performance/io-threads/src/io-threads.c
+++ b/xlators/performance/io-threads/src/io-threads.c
@@ -33,283 +33,126 @@
 #include <time.h>
 #include "locking.h"
 
-typedef void *(*iot_worker_fn)(void*);
+void *iot_worker (void *arg);
+int iot_workers_scale (iot_conf_t *conf);
+int __iot_workers_scale (iot_conf_t *conf);
 
-void
-iot_stop_worker (iot_worker_t *worker);
-
-void
-iot_stop_workers (iot_worker_t **workers, int start_idx, int count);
-
-void
-_iot_queue (iot_worker_t *worker, iot_request_t *req);
-
-iot_request_t *
-iot_init_request (iot_worker_t *conf, call_stub_t *stub);
 
-int
-iot_startup_workers (iot_worker_t **workers, int start_idx, int count,
-                     iot_worker_fn workerfunc);
-
-void *
-iot_worker_unordered (void *arg);
-
-void *
-iot_worker_ordered (void *arg);
-
-int
-iot_startup_worker (iot_worker_t *worker, iot_worker_fn workerfunc);
-
-void
-iot_destroy_request (iot_worker_t *worker, iot_request_t * req);
-
-void
-iot_notify_worker (iot_worker_t *worker)
+call_stub_t *
+__iot_dequeue (iot_conf_t *conf)
 {
-#ifndef HAVE_SPINLOCK
-        pthread_cond_broadcast (&worker->notifier);
-#else
-        sem_post (&worker->notifier);
-#endif
-
-        return;
-}
+        call_stub_t  *stub = NULL;
 
-int
-iot_notify_wait (iot_worker_t *worker, int idletime)
-{
-        struct timeval  tv;
-        struct timespec ts = {0, };
-        int             waitres = 0;
+        if (list_empty (&conf->req))
+                return NULL;
 
-        gettimeofday (&tv, NULL);
-        /* Slightly skew the idle time for threads so that, we dont
-         * have all of them rushing to exit at the same time, if
-         * they've been idle.
-         */
-        ts.tv_sec = skew_sec_idle_time (tv.tv_sec + idletime);
-
-#ifndef HAVE_SPINLOCK
-        waitres = pthread_cond_timedwait (&worker->notifier, &worker->qlock,
-                                          &ts);
-#else
-        UNLOCK (&worker->qlock);
-        errno = 0;
-        waitres = sem_timedwait (&worker->notifier, &ts);
-        LOCK (&worker->qlock);
-        if (waitres < 0)
-                waitres = errno;
-#endif
+        stub = list_entry (conf->req.next, call_stub_t, list);
+        list_del_init (&stub->list);
+        conf->queue_size--;
 
-        return waitres;
+        return stub;
 }
 
+
 void
-iot_notify_init (iot_worker_t *worker)
+__iot_enqueue (iot_conf_t *conf, call_stub_t *stub)
 {
-        if (worker == NULL)
-                return;
-
-        LOCK_INIT (&worker->qlock);
-
-#ifndef HAVE_SPINLOCK
-        pthread_cond_init (&worker->notifier, NULL);
-#else
-        sem_init (&worker->notifier, 0, 0);
-#endif
+        list_add_tail (&stub->list, &conf->req);
+        conf->queue_size++;
 
         return;
 }
 
-/* I know this function modularizes things a bit too much,
- * but it is easier on the eyes to read this than see all that locking,
- * queueing, and thread firing in the same curly block, as was the
- * case before this function.
- */
-int
-iot_request_queue_and_thread_fire (iot_worker_t *worker,
-                                   iot_worker_fn workerfunc, iot_request_t *req)
-{
-        int     ret = -1; 
-        LOCK (&worker->qlock);
-        {
-                if (iot_worker_active (worker)) {
-                        _iot_queue (worker, req);
-                        ret = 0;
-                }else {
-                        ret = iot_startup_worker (worker, workerfunc);
-                        if (ret < 0) {
-                                goto unlock;
-                        }
-                        _iot_queue (worker, req);
-                }
-        }
-unlock:
-        UNLOCK (&worker->qlock);
 
-        return ret;
-}
+void *
+iot_worker (void *data)
+{
+        iot_conf_t       *conf = NULL;
+        xlator_t         *this = NULL;
+        call_stub_t      *stub = NULL;
+        struct timespec   sleep_till = {0, };
+        int               ret = 0;
+        char              timeout = 0;
+        char              bye = 0;
+
+        conf = data;
+        this = conf->this;
+        THIS = this;
+
+        while (1) {
+                sleep_till.tv_sec = time (NULL) + conf->idle_time;
+
+                pthread_mutex_lock (&conf->mutex);
+                {
+                        while (list_empty (&conf->req)) {
+                                conf->sleep_count++;
+
+                                ret = pthread_cond_timedwait (&conf->cond,
+                                                              &conf->mutex,
+                                                              &sleep_till);
+                                conf->sleep_count--;
+
+                                if (ret == -1 && errno == ETIMEDOUT) {
+                                        timeout = 1;
+                                        break;
+                                }
+                        }
 
+                        if (timeout) {
+                                if (conf->curr_count > IOT_MIN_THREADS) {
+                                        conf->curr_count--;
+                                        bye = 1;
+                                } else {
+                                        timeout = 0;
+                                }
+                        }
 
-int
-iot_unordered_request_balancer (iot_conf_t *conf)
-{
-        long int        rand = 0;
-        int             idx = 0;
+                        stub = __iot_dequeue (conf);
+                }
+                pthread_mutex_unlock (&conf->mutex);
 
-        /* Decide which thread will service the request.
-         * FIXME: This should change into some form of load-balancing.
-         * */
-        rand = random ();
+                if (stub) /* guard against spurious wakeups */
+                        call_resume (stub);
 
-        /* If scaling is on, we can choose from any thread
-        * that has been allocated upto, max_o_threads, but
-        * with scaling off, we'll never have threads more
-        * than min_o_threads.
-        */
-        if (iot_unordered_scaling_on (conf))
-                idx = (rand % conf->max_u_threads);
-        else
-                idx = (rand % conf->min_u_threads);
+                if (bye)
+                        break;
+        }
 
-        return idx;
+        return NULL;
 }
 
 
 int
-iot_schedule_unordered (iot_conf_t *conf, inode_t *inode, call_stub_t *stub)
+iot_schedule (iot_conf_t *conf, call_stub_t *stub)
 {
-        int32_t          idx = 0;
-        iot_worker_t    *selected_worker = NULL;
-        iot_request_t   *req = NULL;
-        int             ret = -1;
+        int   ret = 0;
 
-        idx = iot_unordered_request_balancer (conf);
-        selected_worker = conf->uworkers[idx];
+        pthread_mutex_lock (&conf->mutex);
+        {
+                __iot_enqueue (conf, stub);
 
-        req = iot_init_request (selected_worker, stub);
-        if (req == NULL) {
-                ret = -ENOMEM;
-                goto out;
-        }
+                pthread_cond_signal (&conf->cond);
 
-        ret = iot_request_queue_and_thread_fire (selected_worker,
-                                                 iot_worker_unordered, req);
-        if (ret < 0) {
-                iot_destroy_request (selected_worker, req);
+                ret = __iot_workers_scale (conf);
         }
-out:
-        return ret;
-}
-
-
-/* Only to be used with ordered requests.
- */
-uint64_t
-iot_create_inode_worker_assoc (iot_conf_t * conf, inode_t * inode)
-{
-        long int        rand = 0;
-        uint64_t        idx = 0;
-
-        rand = random ();
-        /* If scaling is on, we can choose from any thread
-        * that has been allocated upto, max_o_threads, but
-        * with scaling off, we'll never have threads more
-        * than min_o_threads.
-        */
-        if (iot_ordered_scaling_on (conf))
-                idx = (rand % conf->max_o_threads);
-        else
-                idx = (rand % conf->min_o_threads);
+        pthread_mutex_unlock (&conf->mutex);
 
-        __inode_ctx_put (inode, conf->this, idx);
-
-        return idx;
+        return 0;
 }
 
 
-/* Assumes inode lock is held. */
-int32_t
-iot_ordered_request_balancer (iot_conf_t *conf, inode_t *inode, uint64_t *idx)
+int
+iot_schedule_unordered (iot_conf_t *conf, inode_t *inode, call_stub_t *stub)
 {
-        int ret = -1;
-
-        if (__inode_ctx_get (inode, conf->this, idx) < 0)
-                *idx = iot_create_inode_worker_assoc (conf, inode);
-        else {
-                /* Sanity check to ensure the idx received from the inode
-                * context is within bounds. We're a bit optimistic in
-                * assuming that if an index is within bounds, it is
-                * not corrupted. idx is uint so we dont check for less
-                * than 0.
-                */
-                if ((*idx >= (uint64_t)conf->max_o_threads)) {
-                        gf_log (conf->this->name, GF_LOG_DEBUG,
-                                "inode context returned insane thread index %"
-                                PRIu64, *idx);
-                        ret = -EINVAL;
-                        goto out;
-                }
-        }
-        ret = 0;
-out:
-        return ret;
+        return iot_schedule (conf, stub);
 }
 
 
 int
 iot_schedule_ordered (iot_conf_t *conf, inode_t *inode, call_stub_t *stub)
 {
-        uint64_t         idx = 0;
-        iot_worker_t    *selected_worker = NULL;
-        iot_request_t   *req = NULL;
-        int              balstatus = 0, ret = -1;
-
-        if (inode == NULL) {
-                gf_log (conf->this->name, GF_LOG_DEBUG,
-                        "Got NULL inode for ordered request");
-                ret = -EINVAL;
-                goto out;
-        }
-
-        LOCK (&inode->lock);
-        {
-                balstatus = iot_ordered_request_balancer (conf, inode, &idx);
-                if (balstatus < 0) {
-                        gf_log (conf->this->name, GF_LOG_DEBUG,
-                                "Insane worker index. Unwinding stack");
-                        ret = -ECANCELED;
-                        goto unlock_out;
-                }
-                /* inode lock once acquired, cannot be left here
-                 * because other gluster main threads might be
-                 * contending on it to append a request for this file.
-                 * So we'll also leave the lock only after we've
-                 * added the request to the worker queue.
-                 */
-                selected_worker = conf->oworkers[idx];
-
-                req = iot_init_request (selected_worker, stub);
-                if (req == NULL) {
-                        gf_log (conf->this->name, GF_LOG_ERROR,"out of memory");
-                        ret = -ENOMEM;
-                        goto unlock_out;
-                }
 
-                ret = iot_request_queue_and_thread_fire (selected_worker,
-                                                         iot_worker_ordered,
-                                                         req);
-        }
-unlock_out:
-        UNLOCK (&inode->lock);
-
-out:
-        if (ret < 0) {
-                if (req != NULL) {
-                        iot_destroy_request (selected_worker, req);
-                }
-        }
-        return ret;
+        return iot_schedule (conf, stub);
 }
 
 
@@ -394,7 +237,7 @@ iot_setattr (call_frame_t *frame, xlator_t *this, loc_t *loc,
              struct stat *stbuf, int32_t valid)
 {
         call_stub_t     *stub = NULL;
-        int             ret = -1;
+        int              ret = -1;
 
         stub = fop_setattr_stub (frame, iot_setattr_wrapper, loc, stbuf, valid);
         if (!stub) {
@@ -445,7 +288,7 @@ iot_fsetattr (call_frame_t *frame, xlator_t *this, fd_t *fd,
               struct stat *stbuf, int32_t valid)
 {
         call_stub_t     *stub = NULL;
-        int             ret = -1;
+        int              ret = -1;
 
         stub = fop_fsetattr_stub (frame, iot_fsetattr_wrapper, fd, stbuf,
                                   valid);
@@ -1442,7 +1285,7 @@ iot_checksum_wrapper (call_frame_t *frame, xlator_t *this, loc_t *loc,
 		    FIRST_CHILD(this),
 		    FIRST_CHILD(this)->fops->checksum,
 		    loc, flags);
-  
+
 	return 0;
 }
 
@@ -1494,7 +1337,6 @@ iot_unlink_wrapper (call_frame_t *frame, xlator_t *this, loc_t *loc)
 		    FIRST_CHILD(this),
 		    FIRST_CHILD(this)->fops->unlink,
 		    loc);
-  
 	return 0;
 }
 
@@ -2190,355 +2032,58 @@ out:
 }
 
 
-/* Must be called with worker lock held */
-void
-_iot_queue (iot_worker_t *worker, iot_request_t *req)
-{
-        list_add_tail (&req->list, &worker->rqlist);
-
-        /* dq_cond */
-        worker->queue_size++;
-        iot_notify_worker(worker);
-}
-
-
-iot_request_t *
-iot_init_request (iot_worker_t *worker, call_stub_t *stub)
-{
-	iot_request_t   *req = NULL;
-
-        req = mem_get (worker->req_pool);
-        if (req == NULL) {
-                goto out;
-        }
-
-        req->stub = stub;
-out:
-        return req;
-}
-
-
-void
-iot_destroy_request (iot_worker_t *worker, iot_request_t * req)
-{
-        if ((req == NULL) || (worker == NULL))
-                return;
-
-        mem_put (worker->req_pool, req);
-}
-
-
-/* Must be called with worker lock held. */
-gf_boolean_t
-iot_can_ordered_exit (iot_worker_t * worker)
-{
-        gf_boolean_t     allow_exit = _gf_false;
-        iot_conf_t      *conf = NULL;
-
-        conf = worker->conf;
-        /* We dont want this thread to exit if its index is
-         * below the min thread count.
-         */
-        if (worker->thread_idx >= conf->min_o_threads)
-                allow_exit = _gf_true;
-
-        return allow_exit;
-}
-
-/* Must be called with worker lock held. */
-gf_boolean_t
-iot_ordered_exit (int cond_waitres, iot_worker_t *worker)
-{
-        gf_boolean_t     allow_exit = _gf_false;
-
-        if (worker->state == IOT_STATE_EXIT_REQUEST) {
-                allow_exit = _gf_true;
-        } else if (cond_waitres == ETIMEDOUT) {
-                allow_exit = iot_can_ordered_exit (worker);
-        }
-
-        if (allow_exit) {
-                worker->state = IOT_STATE_DEAD;
-                worker->thread = 0;
-        }
-
-        return allow_exit;
-}
-
-
 int
-iot_ordered_request_wait (iot_worker_t * worker)
+__iot_workers_scale (iot_conf_t *conf)
 {
-        int             waitres = 0;
-        int             retstat = 0;
+        int       log2 = 0;
+        int       scale = 0;
+        int       diff = 0;
+        pthread_t thread;
+        int       ret = 0;
 
-        if (worker->state == IOT_STATE_EXIT_REQUEST) {
-                retstat = -1;
-                goto out;
-        }
+        log2 = log_base2 (conf->queue_size);
 
-        waitres = iot_notify_wait (worker, worker->conf->o_idle_time);
-        if (iot_ordered_exit (waitres, worker)) {
-                retstat = -1;
-        }
+        scale = log2;
 
-out:
-        return retstat;
-}
-
-
-call_stub_t *
-iot_dequeue_ordered (iot_worker_t *worker)
-{
-	call_stub_t     *stub = NULL;
-	iot_request_t   *req = NULL;
-        int              waitstat = 0;
+        if (log2 < IOT_MIN_THREADS)
+                scale = IOT_MIN_THREADS;
 
-	LOCK (&worker->qlock);
-        {
-                while (!worker->queue_size) {
-                        waitstat = 0;
-                        waitstat = iot_ordered_request_wait (worker);
-                        /* We must've timed out and are now required to
-                         * exit.
-                         */
-                        if (waitstat == -1)
-                                goto out;
-                }
+        if (log2 > conf->max_count)
+                scale = IOT_MAX_THREADS;
 
-                list_for_each_entry (req, &worker->rqlist, list)
-                        break;
-                list_del (&req->list);
-                stub = req->stub;
-
-                worker->queue_size--;
+        if (conf->curr_count < scale) {
+                diff = scale - conf->curr_count;
         }
-out:
-	UNLOCK (&worker->qlock);
-        iot_destroy_request (worker, req);
 
-	return stub;
-}
-
-
-void *
-iot_worker_ordered (void *arg)
-{
-        iot_worker_t    *worker = arg;
-        call_stub_t     *stub = NULL;
-
-	while (1) {
+        while (diff) {
+                diff --;
 
-                stub = iot_dequeue_ordered (worker);
-                /* If stub is NULL, we must've timed out waiting for a
-                 * request and have now been allowed to exit.
-                 */
-                if (!stub)
+                ret = pthread_create (&thread, &conf->w_attr, iot_worker, conf);
+                if (ret == 0)
+                        conf->curr_count++;
+                else
                         break;
-		call_resume (stub);
-	}
-
-        return NULL;
-}
-
-
-/* Must be called with worker lock held. */
-gf_boolean_t
-iot_can_unordered_exit (iot_worker_t * worker)
-{
-        gf_boolean_t    allow_exit = _gf_false;
-        iot_conf_t      *conf = NULL;
-
-        conf = worker->conf;
-        /* We dont want this thread to exit if its index is
-         * below the min thread count.
-         */
-        if (worker->thread_idx >= conf->min_u_threads)
-                allow_exit = _gf_true;
-
-        return allow_exit;
-}
-
-
-/* Must be called with worker lock held. */
-gf_boolean_t
-iot_unordered_exit (int cond_waitres, iot_worker_t *worker)
-{
-        gf_boolean_t     allow_exit = _gf_false;
-
-        if (worker->state == IOT_STATE_EXIT_REQUEST) {
-                allow_exit = _gf_true;
-        } else if (cond_waitres == ETIMEDOUT) {
-                allow_exit = iot_can_unordered_exit (worker);
         }
 
-        if (allow_exit) {
-                worker->state = IOT_STATE_DEAD;
-                worker->thread = 0;
-        }
-
-        return allow_exit;
+        return diff;
 }
 
 
 int
-iot_unordered_request_wait (iot_worker_t * worker)
+iot_workers_scale (iot_conf_t *conf)
 {
-        int             waitres = 0;
-        int             retstat = 0;
+        int     ret = -1;
 
-        if (worker->state == IOT_STATE_EXIT_REQUEST) {
-                retstat = -1;
+        if (conf == NULL) {
+                ret = -EINVAL;
                 goto out;
         }
 
-        waitres = iot_notify_wait (worker, worker->conf->u_idle_time);
-        if (iot_unordered_exit (waitres, worker)) {
-                retstat = -1;
-        }
-
-out:
-        return retstat;
-}
-
-
-call_stub_t *
-iot_dequeue_unordered (iot_worker_t *worker)
-{
-        call_stub_t     *stub= NULL;
-        iot_request_t   *req = NULL;
-        int              waitstat = 0;
-
-	LOCK (&worker->qlock);
+        pthread_mutex_lock (&conf->mutex);
         {
-                while (!worker->queue_size) {
-                        waitstat = 0;
-                        waitstat = iot_unordered_request_wait (worker);
-                        /* If -1, request wait must've timed
-                         * out.
-                         */
-                        if (waitstat == -1)
-                                goto out;
-                }
-
-                list_for_each_entry (req, &worker->rqlist, list)
-                        break;
-                list_del (&req->list);
-                stub = req->stub;
-
-                worker->queue_size--;
+                ret = __iot_workers_scale (conf);
         }
-out:
-	UNLOCK (&worker->qlock);
-        iot_destroy_request (worker, req);
-
-	return stub;
-}
-
-
-void *
-iot_worker_unordered (void *arg)
-{
-        iot_worker_t    *worker = arg;
-        call_stub_t     *stub = NULL;
-
-	while (1) {
-
-		stub = iot_dequeue_unordered (worker);
-                /* If no request was received, we must've timed out,
-                 * and can exit. */
-                if (!stub)
-                        break;
-
-		call_resume (stub);
-	}
-
-        return NULL;
-}
-
-
-void
-deallocate_worker_array (iot_worker_t **workers)
-{
-        FREE (workers);
-}
-
-void
-deallocate_workers (iot_worker_t **workers,
-                    int start_alloc_idx, int count)
-{
-        int     i;
-        int     end_count;
-
-        end_count = count + start_alloc_idx;
-        for (i = start_alloc_idx; (i < end_count); i++) {
-                if (workers[i] != NULL) {
-                        mem_pool_destroy (workers[i]->req_pool);
-                        FREE (workers[i]);
-                        workers[i] = NULL;
-                }
-        }
-        
-}
-
-
-iot_worker_t **
-allocate_worker_array (int count)
-{
-        iot_worker_t    **warr = NULL;
-
-        warr = CALLOC (count, sizeof (iot_worker_t *));
-
-        return warr;
-}
-
-
-iot_worker_t *
-allocate_worker (iot_conf_t * conf)
-{
-        iot_worker_t    *wrk = NULL;
-
-        wrk = CALLOC (1, sizeof (iot_worker_t));
-        if (wrk == NULL) {
-                gf_log (conf->this->name, GF_LOG_ERROR, "out of memory");
-                goto out;
-        }
-
-        wrk->req_pool = mem_pool_new (iot_request_t, IOT_REQUEST_MEMPOOL_SIZE);
-        if (wrk->req_pool == NULL)
-                goto free_wrk;
-
-        INIT_LIST_HEAD (&wrk->rqlist);
-        wrk->conf = conf;
-        iot_notify_init (wrk);
-        wrk->state = IOT_STATE_DEAD;
-
-out:
-        return wrk;
-
-free_wrk:
-        FREE (wrk);
-        return NULL;
-}
-
-
-int
-allocate_workers (iot_conf_t *conf, iot_worker_t **workers, int start_alloc_idx,
-                  int count)
-{
-        int     i;
-        int     end_count, ret = -1;
-
-        end_count = count + start_alloc_idx;
-        for (i = start_alloc_idx; i < end_count; i++) {
-                workers[i] = allocate_worker (conf);
-                if (workers[i] == NULL) {
-                        ret = -ENOMEM;
-                        goto out;
-                }
-                workers[i]->thread_idx = i;
-        }
-        ret = 0;
+        pthread_mutex_unlock (&conf->mutex);
 
 out:
         return ret;
@@ -2546,75 +2091,6 @@ out:
 
 
 void
-iot_stop_worker (iot_worker_t *worker)
-{
-        LOCK (&worker->qlock);
-        {
-                worker->state = IOT_STATE_EXIT_REQUEST;
-        }
-        UNLOCK (&worker->qlock);
-
-        iot_notify_worker (worker);
-        pthread_join (worker->thread, NULL);
-}
-
-
-void
-iot_stop_workers (iot_worker_t **workers, int start_idx, int count)
-{
-        int     i = 0;
-        int     end_idx = 0;
-
-        end_idx = start_idx + count;
-        for (i = start_idx; i < end_idx; i++) {
-                if (workers[i] != NULL) {
-                        iot_stop_worker (workers[i]);
-                }
-        }
-}
-
-
-int
-iot_startup_worker (iot_worker_t *worker, iot_worker_fn workerfunc)
-{
-        int     ret = -1;
-        ret = pthread_create (&worker->thread, &worker->conf->w_attr,
-                              workerfunc, worker);
-        if (ret != 0) {
-                gf_log (worker->conf->this->name, GF_LOG_ERROR,
-                        "cannot start worker (%s)", strerror (errno));
-                ret = -ret;
-        } else {
-                worker->state = IOT_STATE_ACTIVE;
-        }
-
-        return ret;
-}
-
-
-int
-iot_startup_workers (iot_worker_t **workers, int start_idx, int count,
-                     iot_worker_fn workerfunc)
-{
-        int     i = 0;
-        int     end_idx = 0;
-        int     ret = -1; 
-
-        end_idx = start_idx + count;
-        for (i = start_idx; i < end_idx; i++) {
-                ret = iot_startup_worker (workers[i], workerfunc);
-                if (ret < 0) {
-                        goto out;
-                }
-        }
-
-        ret = 0;
-out:
-        return ret;
-}
-
-
-void
 set_stack_size (iot_conf_t *conf)
 {
         int     err = 0;
@@ -2624,99 +2100,8 @@ set_stack_size (iot_conf_t *conf)
         err = pthread_attr_setstacksize (&conf->w_attr, stacksize);
         if (err == EINVAL) {
                 gf_log (conf->this->name, GF_LOG_WARNING,
-                                "Using default thread stack size");
-        }
-}
-
-
-void
-iot_cleanup_workers (iot_conf_t *conf)
-{
-        if (conf->uworkers != NULL) {
-                iot_stop_workers (conf->uworkers, 0,
-                                  conf->max_u_threads);
-                    
-                deallocate_workers (conf->uworkers, 0,
-                                    conf->max_u_threads);
-
-                deallocate_worker_array (conf->uworkers);
-        }
-                
-        if (conf->oworkers != NULL) {
-                iot_stop_workers (conf->oworkers, 0,
-                                  conf->max_o_threads);
-                        
-                deallocate_workers (conf->oworkers, 0,
-                                    conf->max_o_threads);
-                        
-                deallocate_worker_array (conf->oworkers);
-        }
-}
-
-
-int
-workers_init (iot_conf_t *conf)
-{
-        int     ret = -1;
-
-        if (conf == NULL) {
-                ret = -EINVAL;
-                goto err;
-        }
-
-        /* Initialize un-ordered workers */
-        conf->uworkers = allocate_worker_array (conf->max_u_threads);
-        if (conf->uworkers == NULL) {
-                gf_log (conf->this->name, GF_LOG_ERROR, "out of memory");
-                ret = -ENOMEM;
-                goto err;
-        }
-
-        ret = allocate_workers (conf, conf->uworkers, 0,
-                                conf->max_u_threads);
-        if (ret < 0) {
-                gf_log (conf->this->name, GF_LOG_ERROR, "out of memory");
-                goto err;
+                        "Using default thread stack size");
         }
-
-        /* Initialize ordered workers */
-        conf->oworkers = allocate_worker_array (conf->max_o_threads);
-        if (conf->oworkers == NULL) {
-                gf_log (conf->this->name, GF_LOG_ERROR, "out of memory");
-                ret = -ENOMEM;
-                goto err;
-        }
-
-        ret = allocate_workers (conf, conf->oworkers, 0,
-                                conf->max_o_threads);
-        if (ret < 0) {
-                gf_log (conf->this->name, GF_LOG_ERROR, "out of memory");
-                goto err;
-        }
-
-        set_stack_size (conf);
-        ret = iot_startup_workers (conf->oworkers, 0, conf->min_o_threads,
-                                   iot_worker_ordered);
-        if (ret == -1) {
-                /* logged inside iot_startup_workers */
-                goto err;
-        }
-
-        ret = iot_startup_workers (conf->uworkers, 0, conf->min_u_threads,
-                                   iot_worker_unordered);
-        if (ret == -1) {
-                /* logged inside iot_startup_workers */
-                goto err;
-        }
-
-        return 0;
-
-err:
-        if (conf != NULL)  {
-                iot_cleanup_workers (conf);
-        }
-
-        return ret;
 }
 
 
@@ -2725,11 +2110,10 @@ init (xlator_t *this)
 {
         iot_conf_t      *conf = NULL;
         dict_t          *options = this->options;
-        int             thread_count = IOT_DEFAULT_THREADS;
-        gf_boolean_t    autoscaling = IOT_SCALING_OFF;
-        char            *scalestr = NULL;
-        int             min_threads, max_threads, ret = -1;
-        
+        int              thread_count = IOT_DEFAULT_THREADS;
+        int              idle_time = IOT_DEFAULT_IDLE;
+        int              ret = 0;
+
 	if (!this->children || this->children->next) {
 		gf_log ("io-threads", GF_LOG_ERROR,
 			"FATAL: iot not configured with exactly one child");
@@ -2748,100 +2132,33 @@ init (xlator_t *this)
                 goto out;
         }
 
-        if ((dict_get_str (options, "autoscaling", &scalestr)) == 0) {
-                if ((gf_string2boolean (scalestr, &autoscaling)) == -1) {
-                        gf_log (this->name, GF_LOG_ERROR,
-                                        "'autoscaling' option must be"
-                                        " boolean");
-                        goto out;
-                }
-        }
+        thread_count = IOT_DEFAULT_THREADS;
 
 	if (dict_get (options, "thread-count")) {
                 thread_count = data_to_int32 (dict_get (options,
-                                        "thread-count"));
-                if (scalestr != NULL)
-                        gf_log (this->name, GF_LOG_WARNING,
-                                        "'thread-count' is specified with "
-                                        "'autoscaling' on. Ignoring"
-                                        "'thread-count' option.");
-                if (thread_count < 2)
+                                                        "thread-count"));
+                if (thread_count < IOT_MIN_THREADS)
                         thread_count = IOT_MIN_THREADS;
-        }
 
-        min_threads = IOT_DEFAULT_THREADS;
-        max_threads = IOT_MAX_THREADS;
-        if (dict_get (options, "min-threads"))
-                min_threads = data_to_int32 (dict_get (options,
-                                        "min-threads"));
+                if (thread_count > IOT_MAX_THREADS)
+                        thread_count = IOT_MAX_THREADS;
+        }
+        conf->max_count = thread_count;
 
-        if (dict_get (options, "max-threads"))
-                max_threads = data_to_int32 (dict_get (options,
-                                        "max-threads"));
-       
-        if (min_threads > max_threads) {
-                gf_log (this->name, GF_LOG_ERROR, " min-threads must be less "
-                                "than max-threads");
-                goto out;
+	if (dict_get (options, "idle-time")) {
+                idle_time = data_to_int32 (dict_get (options,
+                                                     "idle-time"));
+                if (idle_time < 0)
+                        idle_time = 1;
         }
+        conf->idle_time = idle_time;
 
-        /* If autoscaling is off, then adjust the min and max
-         * threads according to thread-count.
-         * This is based on the assumption that despite autoscaling
-         * being off, we still want to have separate pools for data
-         * and meta-data threads.
-         */
-        if (!autoscaling)
-                max_threads = min_threads = thread_count;
+        conf->this = this;
 
-        /* If user specifies an odd number of threads, increase it by
-         * one. The reason for having an even number of threads is
-         * explained later.
-         */
-        if (max_threads % 2)
-                max_threads++;
-
-        if(min_threads % 2)
-                min_threads++;
-
-        /* If the user wants to have only a single thread for
-        * some strange reason, make sure we set this count to
-        * 2. Explained later.
-        */
-        if (min_threads < IOT_MIN_THREADS)
-                min_threads = IOT_MIN_THREADS;
-
-        /* Again, have atleast two. Read on. */
-        if (max_threads < IOT_MIN_THREADS)
-                max_threads = IOT_MIN_THREADS;
-
-        /* This is why we need atleast two threads.
-         * We're dividing the specified thread pool into
-         * 2 halves, equally between ordered and unordered
-         * pools.
-         */
+        INIT_LIST_HEAD (&conf->req);
 
-        /* Init params for un-ordered workers. */
-        pthread_mutex_init (&conf->utlock, NULL);
-        conf->max_u_threads = max_threads / 2;
-        conf->min_u_threads = min_threads / 2;
-        conf->u_idle_time = IOT_DEFAULT_IDLE;
-        conf->u_scaling = autoscaling;
-
-        /* Init params for ordered workers. */
-        pthread_mutex_init (&conf->otlock, NULL);
-        conf->max_o_threads = max_threads / 2;
-        conf->min_o_threads = min_threads / 2;
-        conf->o_idle_time = IOT_DEFAULT_IDLE;
-        conf->o_scaling = autoscaling;
-
-        gf_log (this->name, GF_LOG_DEBUG,
-                "io-threads: Autoscaling: %s, "
-                "min_threads: %d, max_threads: %d",
-                (autoscaling) ? "on":"off", min_threads, max_threads);
+	ret = iot_workers_scale (conf);
 
-        conf->this = this;
-	ret = workers_init (conf);
         if (ret == -1) {
                 gf_log (this->name, GF_LOG_ERROR,
                         "cannot initialize worker threads, exiting init");
@@ -2902,7 +2219,7 @@ struct xlator_fops fops = {
         .opendir     = iot_opendir,     /* U */
         .fsyncdir    = iot_fsyncdir,    /* O */
         .statfs      = iot_statfs,      /* U */
-        .setxattr    = iot_setxattr,     /* U */
+        .setxattr    = iot_setxattr,    /* U */
         .getxattr    = iot_getxattr,    /* U */
         .fgetxattr   = iot_fgetxattr,   /* O */
         .fsetxattr   = iot_fsetxattr,   /* O */
@@ -2920,29 +2237,16 @@ struct xlator_cbks cbks = {
 };
 
 struct volume_options options[] = {
-	{ .key  = {"thread-count"}, 
-	  .type = GF_OPTION_TYPE_INT, 
-	  .min  = IOT_MIN_THREADS, 
+	{ .key  = {"thread-count"},
+	  .type = GF_OPTION_TYPE_INT,
+	  .min  = IOT_MIN_THREADS,
 	  .max  = IOT_MAX_THREADS
 	},
-        { .key  = {"autoscaling"},
-          .type = GF_OPTION_TYPE_BOOL
-        },
-        { .key          = {"min-threads"},
-          .type         = GF_OPTION_TYPE_INT,
-          .min          = IOT_MIN_THREADS,
-          .max          = IOT_MAX_THREADS,
-          .description  = "Minimum number of threads must be greater than or "
-                          "equal to 2. If the specified value is less than 2 "
-                          "it is adjusted upwards to 2. This is a requirement"
-                          " for the current model of threading in io-threads."
+        {.key   = {"idle-time"},
+         .type  = GF_OPTION_TYPE_INT,
+         .min   = 1,
+         .max   = 0x7fffffff,
         },
-        { .key          = {"max-threads"},
-          .type         = GF_OPTION_TYPE_INT,
-          .min          = IOT_MIN_THREADS,
-          .max          = IOT_MAX_THREADS,
-          .description  = "Maximum number of threads is advisory only so the "
-                          "user specified value will be used."
+	{ .key  = {NULL},
         },
-	{ .key  = {NULL} },
 };
diff --git a/xlators/performance/io-threads/src/io-threads.h b/xlators/performance/io-threads/src/io-threads.h
index 3cd959069ba..8b9985be16c 100644
--- a/xlators/performance/io-threads/src/io-threads.h
+++ b/xlators/performance/io-threads/src/io-threads.h
@@ -37,144 +37,38 @@
 #include "locking.h"
 #include <semaphore.h>
 
-#define min(a,b) ((a)<(b)?(a):(b))
-#define max(a,b) ((a)>(b)?(a):(b))
 
 struct iot_conf;
-struct iot_worker;
-struct iot_request;
-
-struct iot_request {
-        struct list_head list;        /* Attaches this request to the list of
-                                         requests.
-                                      */
-        call_stub_t *stub;
-};
-
-typedef enum {
-        IOT_STATE_ACTIVE,
-        IOT_STATE_EXIT_REQUEST,
-        IOT_STATE_DEAD
-}iot_state_t;
-#define iot_worker_active(wrk)  ((wrk)->state == IOT_STATE_ACTIVE)
 
 #define MAX_IDLE_SKEW                   4       /* In secs */
 #define skew_sec_idle_time(sec)         ((sec) + (random () % MAX_IDLE_SKEW))
 #define IOT_DEFAULT_IDLE                180     /* In secs. */
 
-#define IOT_MIN_THREADS         2
-#define IOT_DEFAULT_THREADS     16
+#define IOT_MIN_THREADS         1
+#define IOT_DEFAULT_THREADS     8
 #define IOT_MAX_THREADS         64
 
-#define IOT_SCALING_OFF                 _gf_false
-#define IOT_SCALING_ON                  _gf_true
-#define iot_ordered_scaling_on(conf)    ((conf)->o_scaling == IOT_SCALING_ON)
-#define iot_unordered_scaling_on(conf)  ((conf)->u_scaling == IOT_SCALING_ON)
 
 #define IOT_THREAD_STACK_SIZE   ((size_t)(1024*1024))
 
-/* This signifies the max number of outstanding request we're expecting
- * at a point for every worker thread.
- * For an idea of the memory foot-print, consider at most 16 Bytes per
- * iot_request_t on a 64-bit system with another 16 bytes per chunk in the
- * header. For 64 slots in the pool, we'll use up 2 KiB, with 64 threads this
- * goes up to 128 KiB.
- *
- * Note that this size defines the size of the per-worker mem pool. The
- * advantage is that, we're not only reducing the rate of small iot_request_t
- * allocations from the heap but also reducing the contention on the libc heap
- * by having a mem pool, though small, for each worker.
- */
-#define IOT_REQUEST_MEMPOOL_SIZE        64
-
-struct iot_worker {
-        struct list_head rqlist;      /* List of requests assigned to me. */
-        struct iot_conf  *conf;
-#ifndef HAVE_SPINLOCK
-        pthread_cond_t   notifier;
-#else
-        sem_t            notifier;
-#endif
-        int64_t          q,dq;
-        gf_lock_t        qlock;
-        int32_t          queue_size;
-        pthread_t        thread;
-        iot_state_t      state;            /* What state is the thread in. */
-        int              thread_idx;       /* Thread's index into the worker
-                                              array. Since this will be thread
-                                              local data, for ensuring that
-                                              number of threads dont fall below
-                                              a minimum, we just dont allow
-                                              threads with specific indices to
-                                              exit. Helps us in eliminating one
-                                              place where otherwise a lock
-                                              would have been required to update
-                                              centralized state inside conf.
-                                           */
-        struct mem_pool  *req_pool;    /* iot_request_t's come from here. */
-};
 
 struct iot_conf {
-        int32_t              thread_count;
-        struct iot_worker  **workers;
+        pthread_mutex_t      mutex;
+        pthread_cond_t       cond;
+
+        int32_t              max_count;   /* configured maximum */
+        int32_t              curr_count;  /* actual number of threads running */
+        int32_t              sleep_count;
+
+        int32_t              idle_time;   /* in seconds */
+
+        struct list_head     req;
+        int                  queue_size;
+        pthread_attr_t       w_attr;
 
         xlator_t            *this;
-        /* Config state for ordered threads. */
-        pthread_mutex_t      otlock;       /* Used to sync any state that needs
-                                              to be changed by the ordered
-                                              threads.
-                                           */
-
-        int                  max_o_threads; /* Max. number of ordered threads */
-        int                  min_o_threads; /* Min. number of ordered threads.
-                                               Ordered thread count never falls
-                                               below this threshold.
-                                            */
-
-        int                  o_idle_time;   /* in Secs. The idle time after
-                                               which an ordered thread exits.
-                                            */
-        gf_boolean_t         o_scaling;     /* Set to IOT_SCALING_OFF if user
-                                               does not want thread scaling on
-                                               ordered threads. If scaling is
-                                               off, io-threads maintains at
-                                               least min_o_threads number of
-                                               threads and never lets any thread
-                                               exit.
-                                            */
-        struct iot_worker  **oworkers;      /* Ordered thread pool. */
-
-
-        /* Config state for unordered threads */
-        pthread_mutex_t      utlock;       /* Used for scaling un-ordered
-                                              threads. */
-        struct iot_worker  **uworkers;     /* Un-ordered thread pool. */
-        int                  max_u_threads; /* Number of unordered threads will
-                                               not be higher than this. */
-        int                  min_u_threads; /* Number of unordered threads
-                                               should not fall below this value.
-                                            */
-        int                  u_idle_time;   /* If an unordered thread does not
-                                               get a request for this amount of
-                                               secs, it should try to die.
-                                            */
-        gf_boolean_t         u_scaling;     /* Set to IOT_SCALING_OFF if user
-                                               does not want thread scaling on
-                                               unordered threads. If scaling is
-                                               off, io-threads maintains at
-                                               least min_u_threads number of
-                                               threads and never lets any thread
-                                               exit.
-                                            */
-
-        pthread_attr_t       w_attr;        /* Used to reduce the stack size of
-                                               the pthread worker down from the
-                                               default of 8MiB.
-                                            */
 };
 
 typedef struct iot_conf iot_conf_t;
-typedef struct iot_worker iot_worker_t;
-typedef struct iot_request iot_request_t;
 
 #endif /* __IOT_H */