1 files changed, 279 insertions, 0 deletions
diff --git a/drivers/md/dm-vdo/indexer/funnel-requestqueue.c b/drivers/md/dm-vdo/indexer/funnel-requestqueue.c
new file mode 100644
index 000000000..1a5735375
--- /dev/null
+++ b/drivers/md/dm-vdo/indexer/funnel-requestqueue.c
@@ -0,0 +1,279 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright 2023 Red Hat
+ */
+
+#include "funnel-requestqueue.h"
+
+#include <linux/atomic.h>
+#include <linux/compiler.h>
+#include <linux/wait.h>
+
+#include "funnel-queue.h"
+#include "logger.h"
+#include "memory-alloc.h"
+#include "thread-utils.h"
+
+/*
+ * This queue will attempt to handle requests in reasonably sized batches instead of reacting
+ * immediately to each new request. The wait time between batches is dynamically adjusted up or
+ * down to try to balance responsiveness against wasted thread run time.
+ *
+ * If the wait time becomes long enough, the queue will become dormant and must be explicitly
+ * awoken when a new request is enqueued. The enqueue operation updates "newest" in the funnel
+ * queue via xchg (which is a memory barrier), and later checks "dormant" to decide whether to do a
+ * wakeup of the worker thread.
+ *
+ * When deciding to go to sleep, the worker thread sets "dormant" and then examines "newest" to
+ * decide if the funnel queue is idle. In dormant mode, the last examination of "newest" before
+ * going to sleep is done inside the wait_event_interruptible() macro, after a point where one or
+ * more memory barriers have been issued. (Preparing to sleep uses spin locks.) Even if the funnel
+ * queue's "next" field update isn't visible yet to make the entry accessible, its existence will
+ * kick the worker thread out of dormant mode and back into timer-based mode.
+ *
+ * Unbatched requests are used to communicate between different zone threads and will also cause
+ * the queue to awaken immediately.
+ */
+
+enum {
+	NANOSECOND = 1,
+	MICROSECOND = 1000 * NANOSECOND,
+	MILLISECOND = 1000 * MICROSECOND,
+	DEFAULT_WAIT_TIME = 20 * MICROSECOND,
+	MINIMUM_WAIT_TIME = DEFAULT_WAIT_TIME / 2,
+	MAXIMUM_WAIT_TIME = MILLISECOND,
+	MINIMUM_BATCH = 32,
+	MAXIMUM_BATCH = 64,
+};
+
+struct uds_request_queue {
+	/* Wait queue for synchronizing producers and consumer */
+	struct wait_queue_head wait_head;
+	/* Function to process a request */
+	uds_request_queue_processor_fn processor;
+	/* Queue of new incoming requests */
+	struct funnel_queue *main_queue;
+	/* Queue of old requests to retry */
+	struct funnel_queue *retry_queue;
+	/* The thread id of the worker thread */
+	struct thread *thread;
+	/* True if the worker was started */
+	bool started;
+	/* When true, requests can be enqueued */
+	bool running;
+	/* A flag set when the worker is waiting without a timeout */
+	atomic_t dormant;
+};
+
+static inline struct uds_request *poll_queues(struct uds_request_queue *queue)
+{
+	struct funnel_queue_entry *entry;
+
+	entry = vdo_funnel_queue_poll(queue->retry_queue);
+	if (entry != NULL)
+		return container_of(entry, struct uds_request, queue_link);
+
+	entry = vdo_funnel_queue_poll(queue->main_queue);
+	if (entry != NULL)
+		return container_of(entry, struct uds_request, queue_link);
+
+	return NULL;
+}
+
+static inline bool are_queues_idle(struct uds_request_queue *queue)
+{
+	return vdo_is_funnel_queue_idle(queue->retry_queue) &&
+	       vdo_is_funnel_queue_idle(queue->main_queue);
+}
+
+/*
+ * Determine if there is a next request to process, and return it if there is. Also return flags
+ * indicating whether the worker thread can sleep (for the use of wait_event() macros) and whether
+ * the thread did sleep before returning a new request.
+ */
+static inline bool dequeue_request(struct uds_request_queue *queue,
+				   struct uds_request **request_ptr, bool *waited_ptr)
+{
+	struct uds_request *request = poll_queues(queue);
+
+	if (request != NULL) {
+		*request_ptr = request;
+		return true;
+	}
+
+	if (!READ_ONCE(queue->running)) {
+		/* Wake the worker thread so it can exit. */
+		*request_ptr = NULL;
+		return true;
+	}
+
+	*request_ptr = NULL;
+	*waited_ptr = true;
+	return false;
+}
+
+static void wait_for_request(struct uds_request_queue *queue, bool dormant,
+			     unsigned long timeout, struct uds_request **request,
+			     bool *waited)
+{
+	if (dormant) {
+		wait_event_interruptible(queue->wait_head,
+					 (dequeue_request(queue, request, waited) ||
+					  !are_queues_idle(queue)));
+		return;
+	}
+
+	wait_event_interruptible_hrtimeout(queue->wait_head,
+					   dequeue_request(queue, request, waited),
+					   ns_to_ktime(timeout));
+}
+
+static void request_queue_worker(void *arg)
+{
+	struct uds_request_queue *queue = arg;
+	struct uds_request *request = NULL;
+	unsigned long time_batch = DEFAULT_WAIT_TIME;
+	bool dormant = atomic_read(&queue->dormant);
+	bool waited = false;
+	long current_batch = 0;
+
+	for (;;) {
+		wait_for_request(queue, dormant, time_batch, &request, &waited);
+		if (likely(request != NULL)) {
+			current_batch++;
+			queue->processor(request);
+		} else if (!READ_ONCE(queue->running)) {
+			break;
+		}
+
+		if (dormant) {
+			/*
+			 * The queue has been roused from dormancy. Clear the flag so enqueuers can
+			 * stop broadcasting. No fence is needed for this transition.
+			 */
+			atomic_set(&queue->dormant, false);
+			dormant = false;
+			time_batch = DEFAULT_WAIT_TIME;
+		} else if (waited) {
+			/*
+			 * We waited for this request to show up. Adjust the wait time to smooth
+			 * out the batch size.
+			 */
+			if (current_batch < MINIMUM_BATCH) {
+				/*
+				 * If the last batch of requests was too small, increase the wait
+				 * time.
+				 */
+				time_batch += time_batch / 4;
+				if (time_batch >= MAXIMUM_WAIT_TIME) {
+					atomic_set(&queue->dormant, true);
+					dormant = true;
+				}
+			} else if (current_batch > MAXIMUM_BATCH) {
+				/*
+				 * If the last batch of requests was too large, decrease the wait
+				 * time.
+				 */
+				time_batch -= time_batch / 4;
+				if (time_batch < MINIMUM_WAIT_TIME)
+					time_batch = MINIMUM_WAIT_TIME;
+			}
+			current_batch = 0;
+		}
+	}
+
+	/*
+	 * Ensure that we process any remaining requests that were enqueued before trying to shut
+	 * down. The corresponding write barrier is in uds_request_queue_finish().
+	 */
+	smp_rmb();
+	while ((request = poll_queues(queue)) != NULL)
+		queue->processor(request);
+}
+
+int uds_make_request_queue(const char *queue_name,
+			   uds_request_queue_processor_fn processor,
+			   struct uds_request_queue **queue_ptr)
+{
+	int result;
+	struct uds_request_queue *queue;
+
+	result = vdo_allocate(1, struct uds_request_queue, __func__, &queue);
+	if (result != VDO_SUCCESS)
+		return result;
+
+	queue->processor = processor;
+	queue->running = true;
+	atomic_set(&queue->dormant, false);
+	init_waitqueue_head(&queue->wait_head);
+
+	result = vdo_make_funnel_queue(&queue->main_queue);
+	if (result != VDO_SUCCESS) {
+		uds_request_queue_finish(queue);
+		return result;
+	}
+
+	result = vdo_make_funnel_queue(&queue->retry_queue);
+	if (result != VDO_SUCCESS) {
+		uds_request_queue_finish(queue);
+		return result;
+	}
+
+	result = vdo_create_thread(request_queue_worker, queue, queue_name,
+				   &queue->thread);
+	if (result != VDO_SUCCESS) {
+		uds_request_queue_finish(queue);
+		return result;
+	}
+
+	queue->started = true;
+	*queue_ptr = queue;
+	return UDS_SUCCESS;
+}
+
+static inline void wake_up_worker(struct uds_request_queue *queue)
+{
+	if (wq_has_sleeper(&queue->wait_head))
+		wake_up(&queue->wait_head);
+}
+
+void uds_request_queue_enqueue(struct uds_request_queue *queue,
+			       struct uds_request *request)
+{
+	struct funnel_queue *sub_queue;
+	bool unbatched = request->unbatched;
+
+	sub_queue = request->requeued ? queue->retry_queue : queue->main_queue;
+	vdo_funnel_queue_put(sub_queue, &request->queue_link);
+
+	/*
+	 * We must wake the worker thread when it is dormant. A read fence isn't needed here since
+	 * we know the queue operation acts as one.
+	 */
+	if (atomic_read(&queue->dormant) || unbatched)
+		wake_up_worker(queue);
+}
+
+void uds_request_queue_finish(struct uds_request_queue *queue)
+{
+	if (queue == NULL)
+		return;
+
+	/*
+	 * This memory barrier ensures that any requests we queued will be seen. The point is that
+	 * when dequeue_request() sees the following update to the running flag, it will also be
+	 * able to see any change we made to a next field in the funnel queue entry. The
+	 * corresponding read barrier is in request_queue_worker().
+	 */
+	smp_wmb();
+	WRITE_ONCE(queue->running, false);
+
+	if (queue->started) {
+		wake_up_worker(queue);
+		vdo_join_threads(queue->thread);
+	}
+
+	vdo_free_funnel_queue(queue->main_queue);
+	vdo_free_funnel_queue(queue->retry_queue);
+	vdo_free(queue);
+}