/*-
 * Public Domain 2014-2018 MongoDB, Inc.
 * Public Domain 2008-2014 WiredTiger, Inc.
 *
 * This is free and unencumbered software released into the public domain.
 *
 * Anyone is free to copy, modify, publish, use, compile, sell, or
 * distribute this software, either in source code form or as a compiled
 * binary, for any purpose, commercial or non-commercial, and by any
 * means.
 *
 * In jurisdictions that recognize copyright laws, the author or authors
 * of this software dedicate any and all copyright interest in the
 * software to the public domain. We make this dedication for the benefit
 * of the public at large and to the detriment of our heirs and
 * successors. We intend this dedication to be an overt act of
 * relinquishment in perpetuity of all present and future rights to this
 * software under copyright law.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
 * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
 * IN NO EVENT SHALL THE AUTHORS BE LIABLE FOR ANY CLAIM, DAMAGES OR
 * OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
 * ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
 * OTHER DEALINGS IN THE SOFTWARE.
 */

#include "wtperf.h"

/*
 * Put the initial config together for running a throttled workload.
 */
void
setup_throttle(WTPERF_THREAD *thread)
{
	THROTTLE_CONFIG *throttle_cfg;

	throttle_cfg = &thread->throttle_cfg;

	/*
	 * Setup how the number of operations to run each interval in order to
	 * meet our desired max throughput.
	 * - If we have a very small number of them we can do one op
	 *   on a larger increment. Given there is overhead in throttle logic
	 *   we want to avoid running the throttle check regularly.
	 * - For most workloads, we aim to do 100 ops per interval and adjust
	 *   the sleep period accordingly.
	 * - For high throughput workloads, we aim to do many ops in 100us
	 *   increments.
	 */

	if (thread->workload->throttle < THROTTLE_OPS) {
		/* If the interval is very small, we do one operation */
		throttle_cfg->usecs_increment =
		    USEC_PER_SEC / thread->workload->throttle;
		throttle_cfg->ops_per_increment = 1;
	} else if (thread->workload->throttle < USEC_PER_SEC / THROTTLE_OPS) {
		throttle_cfg->usecs_increment =
		    USEC_PER_SEC / thread->workload->throttle * THROTTLE_OPS;
		throttle_cfg->ops_per_increment = THROTTLE_OPS;
	} else {
		/* If the interval is large, we do more ops per interval */
		throttle_cfg->usecs_increment = USEC_PER_SEC / THROTTLE_OPS;
		throttle_cfg->ops_per_increment =
		    thread->workload->throttle / THROTTLE_OPS;
	}

	/* Give the queue some initial operations to work with */
	throttle_cfg->ops_count = throttle_cfg->ops_per_increment;

	/* Set the first timestamp of when we incremented */
	__wt_epoch(NULL, &throttle_cfg->last_increment);
}

/*
 * Run the throttle function.  We will sleep if needed and then reload the
 * counter to perform more operations.
 */
void
worker_throttle(WTPERF_THREAD *thread)
{
	THROTTLE_CONFIG *throttle_cfg;
	struct timespec now;
	uint64_t usecs_delta;

	throttle_cfg = &thread->throttle_cfg;

	__wt_epoch(NULL, &now);

	/*
	 * If we did enough operations in the current interval, sleep for
	 * the rest of the interval. Then add more operations to the queue.
	 */
	usecs_delta = WT_TIMEDIFF_US(now, throttle_cfg->last_increment);
	if (usecs_delta < throttle_cfg->usecs_increment) {
		(void)usleep(
		    (useconds_t)(throttle_cfg->usecs_increment - usecs_delta));
		throttle_cfg->ops_count =
		     throttle_cfg->ops_per_increment;
		/*
		 * After sleeping, set the interval to the current time.
		 */
		__wt_epoch(NULL, &throttle_cfg->last_increment);
	} else {
		throttle_cfg->ops_count = (usecs_delta *
		    throttle_cfg->ops_per_increment) /
		    throttle_cfg->usecs_increment;
		throttle_cfg->last_increment = now;
	}

	/*
	 * Take the minimum so we don't overfill the queue.
	 */
	throttle_cfg->ops_count =
	    WT_MIN(throttle_cfg->ops_count, thread->workload->throttle);
}
