io-threads: Change mutexes/condvars to spinlocks/semaphores

It seems that use of mutexes is resulting in pretty high thread
sleep and wake-up cost. What is worse, if a worker thread has
acquired a  lock, there is a possibility of the main glusterfs thread
being put to sleep. We change the use of mutexes into spinlock.
At the same time, we cannot anymore use condvars for notification since
the condvar interface depends on mutexes itself. Semaphores come to
out rescue. Luckily, even the pthread semaphores have a timedwait
interface to allow our idle worker threads to make an exit decision.

Further, it is possible that spinlocks are not available on all systems
so all this is curtained behind #defines so we can fall back to
mutexes and condvars implementation.

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

1 files changed, 72 insertions, 34 deletions

diff --git a/xlators/performance/io-threads/src/io-threads.c b/xlators/performance/io-threads/src/io-threads.c
index a0d5d97df67..a04f664e816 100644
--- a/xlators/performance/io-threads/src/io-threads.c
+++ b/xlators/performance/io-threads/src/io-threads.c
@@ -31,6 +31,7 @@
 #include <stdlib.h>
 #include <sys/time.h>
 #include <time.h>
+#include "locking.h"
 
 typedef void *(*iot_worker_fn)(void*);
 
@@ -62,6 +63,64 @@ 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)
+{
+#ifndef HAVE_SPINLOCK
+        pthread_cond_broadcast (&worker->notifier);
+#else
+        sem_post (&worker->notifier);
+#endif
+
+        return;
+}
+
+int
+iot_notify_wait (iot_worker_t *worker, int idletime)
+{
+        struct timeval  tv;
+        struct timespec ts;
+        int             waitres = 0;
+
+        gettimeofday (&tv, NULL);
+        ts.tv_sec = tv.tv_sec + idletime;
+        /* 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_nsec = skew_usec_idle_time (tv.tv_usec) * 1000;
+
+#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
+
+        return waitres;
+}
+
+void
+iot_notify_init (iot_worker_t *worker)
+{
+        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
+
+        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,
@@ -73,7 +132,7 @@ iot_request_queue_and_thread_fire (iot_worker_t *worker,
                                    iot_worker_fn workerfunc, iot_request_t *req)
 {
         int     ret = -1; 
-        pthread_mutex_lock (&worker->qlock);
+        LOCK (&worker->qlock);
         {
                 if (iot_worker_active (worker)) {
                         _iot_queue (worker, req);
@@ -87,7 +146,7 @@ iot_request_queue_and_thread_fire (iot_worker_t *worker,
                 }
         }
 unlock:
-        pthread_mutex_unlock (&worker->qlock);
+        UNLOCK (&worker->qlock);
 
         return ret;
 }
@@ -2229,7 +2288,7 @@ _iot_queue (iot_worker_t *worker, iot_request_t *req)
 
         /* dq_cond */
         worker->queue_size++;
-        pthread_cond_broadcast (&worker->dq_cond);
+        iot_notify_worker(worker);
 }
 
 
@@ -2300,8 +2359,6 @@ iot_ordered_exit (int cond_waitres, iot_worker_t *worker)
 int
 iot_ordered_request_wait (iot_worker_t * worker)
 {
-        struct timeval  tv;
-        struct timespec ts;
         int             waitres = 0;
         int             retstat = 0;
 
@@ -2310,15 +2367,7 @@ iot_ordered_request_wait (iot_worker_t * worker)
                 goto out;
         }
 
-        gettimeofday (&tv, NULL);
-        ts.tv_sec = tv.tv_sec + worker->conf->o_idle_time;
-        /* 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_nsec = skew_usec_idle_time (tv.tv_usec) * 1000;
-        waitres = pthread_cond_timedwait (&worker->dq_cond, &worker->qlock,
-                                          &ts);
+        waitres = iot_notify_wait (worker, worker->conf->o_idle_time);
         if (iot_ordered_exit (waitres, worker)) {
                 retstat = -1;
         }
@@ -2335,7 +2384,7 @@ iot_dequeue_ordered (iot_worker_t *worker)
 	iot_request_t   *req = NULL;
         int              waitstat = 0;
 
-	pthread_mutex_lock (&worker->qlock);
+	LOCK (&worker->qlock);
         {
                 while (!worker->queue_size) {
                         waitstat = 0;
@@ -2355,7 +2404,7 @@ iot_dequeue_ordered (iot_worker_t *worker)
                 worker->queue_size--;
         }
 out:
-	pthread_mutex_unlock (&worker->qlock);
+	UNLOCK (&worker->qlock);
         iot_destroy_request (worker, req);
 
 	return stub;
@@ -2425,8 +2474,6 @@ iot_unordered_exit (int cond_waitres, iot_worker_t *worker)
 int
 iot_unordered_request_wait (iot_worker_t * worker)
 {
-        struct timeval  tv;
-        struct timespec ts;
         int             waitres = 0;
         int             retstat = 0;
 
@@ -2435,15 +2482,7 @@ iot_unordered_request_wait (iot_worker_t * worker)
                 goto out;
         }
 
-        gettimeofday (&tv, NULL);
-        ts.tv_sec = tv.tv_sec + worker->conf->u_idle_time;
-        /* 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_nsec = skew_usec_idle_time (tv.tv_usec) * 1000;
-        waitres = pthread_cond_timedwait (&worker->dq_cond, &worker->qlock,
-                                          &ts);
+        waitres = iot_notify_wait (worker, worker->conf->u_idle_time);
         if (iot_unordered_exit (waitres, worker)) {
                 retstat = -1;
         }
@@ -2460,7 +2499,7 @@ iot_dequeue_unordered (iot_worker_t *worker)
         iot_request_t   *req = NULL;
         int              waitstat = 0;
 
-	pthread_mutex_lock (&worker->qlock);
+	LOCK (&worker->qlock);
         {
                 while (!worker->queue_size) {
                         waitstat = 0;
@@ -2480,7 +2519,7 @@ iot_dequeue_unordered (iot_worker_t *worker)
                 worker->queue_size--;
         }
 out:
-	pthread_mutex_unlock (&worker->qlock);
+	UNLOCK (&worker->qlock);
         iot_destroy_request (worker, req);
 
 	return stub;
@@ -2560,8 +2599,7 @@ allocate_worker (iot_conf_t * conf)
 
         INIT_LIST_HEAD (&wrk->rqlist);
         wrk->conf = conf;
-        pthread_cond_init (&wrk->dq_cond, NULL);
-        pthread_mutex_init (&wrk->qlock, NULL);
+        iot_notify_init (wrk);
         wrk->state = IOT_STATE_DEAD;
 
 out:
@@ -2599,13 +2637,13 @@ out:
 void
 iot_stop_worker (iot_worker_t *worker)
 {
-        pthread_mutex_lock (&worker->qlock);
+        LOCK (&worker->qlock);
         {
                 worker->state = IOT_STATE_EXIT_REQUEST;
         }
-        pthread_mutex_unlock (&worker->qlock);
+        UNLOCK (&worker->qlock);
 
-        pthread_cond_broadcast (&worker->dq_cond);
+        iot_notify_worker (worker);
         pthread_join (worker->thread, NULL);
 }