v4.19.13 snapshot.
diff --git a/include/linux/dynamic_queue_limits.h b/include/linux/dynamic_queue_limits.h
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+++ b/include/linux/dynamic_queue_limits.h
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+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Dynamic queue limits (dql) - Definitions
+ *
+ * Copyright (c) 2011, Tom Herbert <therbert@google.com>
+ *
+ * This header file contains the definitions for dynamic queue limits (dql).
+ * dql would be used in conjunction with a producer/consumer type queue
+ * (possibly a HW queue). Such a queue would have these general properties:
+ *
+ * 1) Objects are queued up to some limit specified as number of objects.
+ * 2) Periodically a completion process executes which retires consumed
+ * objects.
+ * 3) Starvation occurs when limit has been reached, all queued data has
+ * actually been consumed, but completion processing has not yet run
+ * so queuing new data is blocked.
+ * 4) Minimizing the amount of queued data is desirable.
+ *
+ * The goal of dql is to calculate the limit as the minimum number of objects
+ * needed to prevent starvation.
+ *
+ * The primary functions of dql are:
+ * dql_queued - called when objects are enqueued to record number of objects
+ * dql_avail - returns how many objects are available to be queued based
+ * on the object limit and how many objects are already enqueued
+ * dql_completed - called at completion time to indicate how many objects
+ * were retired from the queue
+ *
+ * The dql implementation does not implement any locking for the dql data
+ * structures, the higher layer should provide this. dql_queued should
+ * be serialized to prevent concurrent execution of the function; this
+ * is also true for dql_completed. However, dql_queued and dlq_completed can
+ * be executed concurrently (i.e. they can be protected by different locks).
+ */
+
+#ifndef _LINUX_DQL_H
+#define _LINUX_DQL_H
+
+#ifdef __KERNEL__
+
+struct dql {
+ /* Fields accessed in enqueue path (dql_queued) */
+ unsigned int num_queued; /* Total ever queued */
+ unsigned int adj_limit; /* limit + num_completed */
+ unsigned int last_obj_cnt; /* Count at last queuing */
+
+ /* Fields accessed only by completion path (dql_completed) */
+
+ unsigned int limit ____cacheline_aligned_in_smp; /* Current limit */
+ unsigned int num_completed; /* Total ever completed */
+
+ unsigned int prev_ovlimit; /* Previous over limit */
+ unsigned int prev_num_queued; /* Previous queue total */
+ unsigned int prev_last_obj_cnt; /* Previous queuing cnt */
+
+ unsigned int lowest_slack; /* Lowest slack found */
+ unsigned long slack_start_time; /* Time slacks seen */
+
+ /* Configuration */
+ unsigned int max_limit; /* Max limit */
+ unsigned int min_limit; /* Minimum limit */
+ unsigned int slack_hold_time; /* Time to measure slack */
+};
+
+/* Set some static maximums */
+#define DQL_MAX_OBJECT (UINT_MAX / 16)
+#define DQL_MAX_LIMIT ((UINT_MAX / 2) - DQL_MAX_OBJECT)
+
+/*
+ * Record number of objects queued. Assumes that caller has already checked
+ * availability in the queue with dql_avail.
+ */
+static inline void dql_queued(struct dql *dql, unsigned int count)
+{
+ BUG_ON(count > DQL_MAX_OBJECT);
+
+ dql->last_obj_cnt = count;
+
+ /* We want to force a write first, so that cpu do not attempt
+ * to get cache line containing last_obj_cnt, num_queued, adj_limit
+ * in Shared state, but directly does a Request For Ownership
+ * It is only a hint, we use barrier() only.
+ */
+ barrier();
+
+ dql->num_queued += count;
+}
+
+/* Returns how many objects can be queued, < 0 indicates over limit. */
+static inline int dql_avail(const struct dql *dql)
+{
+ return READ_ONCE(dql->adj_limit) - READ_ONCE(dql->num_queued);
+}
+
+/* Record number of completed objects and recalculate the limit. */
+void dql_completed(struct dql *dql, unsigned int count);
+
+/* Reset dql state */
+void dql_reset(struct dql *dql);
+
+/* Initialize dql state */
+void dql_init(struct dql *dql, unsigned int hold_time);
+
+#endif /* _KERNEL_ */
+
+#endif /* _LINUX_DQL_H */