perf/io-threads: least-rate-limit least priority throttling

The 'least-rate-limit' io-threads translator option enables
throttling of least priority operations. This is initially intended
as a debug/diagnostic tool for users who might experience
overloaded servers via background activity (i.e., self-heal).

least-rate-limit defines the maximum number of least priority
operations the io-threads translator will dequeue in one second.
If the specified rate limit is met, the worker threads sleep for
the minimal amount of time before the next least priority operation
becomes available (or until a new request arrives).

The requests/second metric is generic and relative to a variety of
factors involved with a background operation (server, storage,
etc.). The most recent measured rate ("cached least rate") is added
to the io-threads state dump content (kill -USR1) to serve as a
reference point to throttle background activity under particular
conditions.

Change-Id: I80f2282992137d57b1becaa5c6ae3858c066862a
BUG: 853680
Signed-off-by: Brian Foster <bfoster@redhat.com>
Reviewed-on: http://review.gluster.org/4119
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Anand Avati <avati@redhat.com>

2 files changed, 94 insertions, 2 deletions

diff --git a/xlators/performance/io-threads/src/io-threads.c b/xlators/performance/io-threads/src/io-threads.c
index 2a5cec7edc2..dbf1929e897 100644
--- a/xlators/performance/io-threads/src/io-threads.c
+++ b/xlators/performance/io-threads/src/io-threads.c
@@ -30,16 +30,69 @@ int __iot_workers_scale (iot_conf_t *conf);
 struct volume_options options[];
 
 call_stub_t *
-__iot_dequeue (iot_conf_t *conf, int *pri)
+__iot_dequeue (iot_conf_t *conf, int *pri, struct timespec *sleep)
 {
         call_stub_t  *stub = NULL;
         int           i = 0;
+	struct timeval curtv = {0,}, difftv = {0,};
 
         *pri = -1;
+	sleep->tv_sec = 0;
+	sleep->tv_nsec = 0;
         for (i = 0; i < IOT_PRI_MAX; i++) {
                 if (list_empty (&conf->reqs[i]) ||
                    (conf->ac_iot_count[i] >= conf->ac_iot_limit[i]))
                         continue;
+
+		if (i == IOT_PRI_LEAST) {
+			pthread_mutex_lock(&conf->throttle.lock);
+			if (!conf->throttle.sample_time.tv_sec) {
+				/* initialize */
+				gettimeofday(&conf->throttle.sample_time, NULL);
+			} else {
+				/*
+				 * Maintain a running count of least priority
+				 * operations that are handled over a particular
+				 * time interval. The count is provided via
+				 * state dump and is used as a measure against
+				 * least priority op throttling.
+				 */
+				gettimeofday(&curtv, NULL);
+				timersub(&curtv, &conf->throttle.sample_time,
+					 &difftv);
+				if (difftv.tv_sec >= IOT_LEAST_THROTTLE_DELAY) {
+					conf->throttle.cached_rate =
+						conf->throttle.sample_cnt;
+					conf->throttle.sample_cnt = 0;
+					conf->throttle.sample_time = curtv;
+				}
+
+				/*
+				 * If we're over the configured rate limit,
+				 * provide an absolute time to the caller that
+				 * represents the soonest we're allowed to
+				 * return another least priority request.
+				 */
+				if (conf->throttle.rate_limit &&
+				    conf->throttle.sample_cnt >=
+						conf->throttle.rate_limit) {
+					struct timeval delay;
+					delay.tv_sec = IOT_LEAST_THROTTLE_DELAY;
+					delay.tv_usec = 0;
+
+					timeradd(&conf->throttle.sample_time,
+						 &delay, &curtv);
+					TIMEVAL_TO_TIMESPEC(&curtv, sleep);
+
+					pthread_mutex_unlock(
+						&conf->throttle.lock);
+					break;
+				}
+			}
+			conf->throttle.sample_cnt++;
+			pthread_mutex_unlock(&conf->throttle.lock);
+		}
+
                 stub = list_entry (conf->reqs[i].next, call_stub_t, list);
                 conf->ac_iot_count[i]++;
                 *pri = i;
@@ -83,6 +136,7 @@ iot_worker (void *data)
         int               pri = -1;
         char              timeout = 0;
         char              bye = 0;
+	struct timespec	  sleep = {0,};
 
         conf = data;
         this = conf->this;
@@ -123,7 +177,13 @@ iot_worker (void *data)
                                 }
                         }
 
-                        stub = __iot_dequeue (conf, &pri);
+                        stub = __iot_dequeue (conf, &pri, &sleep);
+			if (!stub && (sleep.tv_sec || sleep.tv_nsec)) {
+				pthread_cond_timedwait(&conf->cond,
+						       &conf->mutex, &sleep);
+				pthread_mutex_unlock(&conf->mutex);
+				continue;
+			}
                 }
                 pthread_mutex_unlock (&conf->mutex);
 
@@ -2485,6 +2545,10 @@ iot_priv_dump (xlator_t *this)
         gf_proc_dump_write("least_priority_threads", "%d",
                            conf->ac_iot_limit[IOT_PRI_LEAST]);
 
+	gf_proc_dump_write("cached least rate", "%u",
+			   conf->throttle.cached_rate);
+	gf_proc_dump_write("least rate limit", "%u", conf->throttle.rate_limit);
+
         return 0;
 }
 
@@ -2516,6 +2580,9 @@ reconfigure (xlator_t *this, dict_t *options)
         GF_OPTION_RECONF ("enable-least-priority", conf->least_priority,
                           options, bool, out);
 
+	GF_OPTION_RECONF("least-rate-limit", conf->throttle.rate_limit, options,
+			 int32, out);
+
 	ret = 0;
 out:
 	return ret;
@@ -2580,6 +2647,14 @@ init (xlator_t *this)
         GF_OPTION_INIT ("enable-least-priority", conf->least_priority,
                         bool, out);
 
+	GF_OPTION_INIT("least-rate-limit", conf->throttle.rate_limit, int32,
+		       out);
+        if ((ret = pthread_mutex_init(&conf->throttle.lock, NULL)) != 0) {
+                gf_log (this->name, GF_LOG_ERROR,
+                        "pthread_mutex_init failed (%d)", ret);
+                goto out;
+        }
+
         conf->this = this;
 
         for (i = 0; i < IOT_PRI_MAX; i++) {
@@ -2722,6 +2797,13 @@ struct volume_options options[] = {
          .max   = 0x7fffffff,
          .default_value = "120",
         },
+	{.key	= {"least-rate-limit"},
+	 .type	= GF_OPTION_TYPE_INT,
+	 .min	= 0,
+	 .default_value = "0",
+	 .description = "Max number of least priority operations to handle "
+			"per-second"
+	},
 	{ .key  = {NULL},
         },
 };
diff --git a/xlators/performance/io-threads/src/io-threads.h b/xlators/performance/io-threads/src/io-threads.h
index a6b640884d0..1a9dee9ae2c 100644
--- a/xlators/performance/io-threads/src/io-threads.h
+++ b/xlators/performance/io-threads/src/io-threads.h
@@ -53,6 +53,14 @@ typedef enum {
         IOT_PRI_MAX,
 } iot_pri_t;
 
+#define IOT_LEAST_THROTTLE_DELAY 1	/* sample interval in seconds */
+struct iot_least_throttle {
+	struct timeval	sample_time;	/* timestamp of current sample */
+	uint32_t	sample_cnt;	/* sample count for active interval */
+	uint32_t	cached_rate;	/* the most recently measured rate */
+	int32_t		rate_limit;	/* user-specified rate limit */
+	pthread_mutex_t	lock;
+};
 
 struct iot_conf {
         pthread_mutex_t      mutex;
@@ -75,6 +83,8 @@ struct iot_conf {
 
         xlator_t            *this;
         size_t              stack_size;
+
+	struct iot_least_throttle throttle;
 };
 
 typedef struct iot_conf iot_conf_t;