diff --git a/include/linux/dynamic_queue_limits.h b/include/linux/dynamic_queue_limits.h
new file mode 100644
index 000000000000..5621547d631b
--- /dev/null
+++ b/include/linux/dynamic_queue_limits.h
@@ -0,0 +1,97 @@
+/*
+ * 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->num_queued += count;
+ dql->last_obj_cnt = count;
+}
+
+/* Returns how many objects can be queued, < 0 indicates over limit. */
+static inline int dql_avail(const struct dql *dql)
+{
+ return dql->adj_limit - 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 */
+int dql_init(struct dql *dql, unsigned hold_time);
+
+#endif /* _KERNEL_ */
+
+#endif /* _LINUX_DQL_H */
diff --git a/lib/Kconfig b/lib/Kconfig
index 32f3e5ae2be5..63b5782732ed 100644
--- a/lib/Kconfig
+++ b/lib/Kconfig
@@ -244,6 +244,9 @@ config CPU_RMAP
bool
depends on SMP
+config DQL
+ bool
+
#
# Netlink attribute parsing support is select'ed if needed
#
diff --git a/lib/Makefile b/lib/Makefile
index a4da283f5dc0..ff00d4dcb7ed 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -115,6 +115,8 @@ obj-$(CONFIG_CPU_RMAP) += cpu_rmap.o
obj-$(CONFIG_CORDIC) += cordic.o
+obj-$(CONFIG_DQL) += dynamic_queue_limits.o
+
hostprogs-y := gen_crc32table
clean-files := crc32table.h
diff --git a/lib/dynamic_queue_limits.c b/lib/dynamic_queue_limits.c
new file mode 100644
index 000000000000..3d1bdcdd7db4
--- /dev/null
+++ b/lib/dynamic_queue_limits.c
@@ -0,0 +1,133 @@
+/*
+ * Dynamic byte queue limits. See include/linux/dynamic_queue_limits.h
+ *
+ * Copyright (c) 2011, Tom Herbert <therbert@google.com>
+ */
+#include <linux/module.h>
+#include <linux/types.h>
+#include <linux/ctype.h>
+#include <linux/kernel.h>
+#include <linux/dynamic_queue_limits.h>
+
+#define POSDIFF(A, B) ((A) > (B) ? (A) - (B) : 0)
+
+/* Records completed count and recalculates the queue limit */
+void dql_completed(struct dql *dql, unsigned int count)
+{
+ unsigned int inprogress, prev_inprogress, limit;
+ unsigned int ovlimit, all_prev_completed, completed;
+
+ /* Can't complete more than what's in queue */
+ BUG_ON(count > dql->num_queued - dql->num_completed);
+
+ completed = dql->num_completed + count;
+ limit = dql->limit;
+ ovlimit = POSDIFF(dql->num_queued - dql->num_completed, limit);
+ inprogress = dql->num_queued - completed;
+ prev_inprogress = dql->prev_num_queued - dql->num_completed;
+ all_prev_completed = POSDIFF(completed, dql->prev_num_queued);
+
+ if ((ovlimit && !inprogress) ||
+ (dql->prev_ovlimit && all_prev_completed)) {
+ /*
+ * Queue considered starved if:
+ * - The queue was over-limit in the last interval,
+ * and there is no more data in the queue.
+ * OR
+ * - The queue was over-limit in the previous interval and
+ * when enqueuing it was possible that all queued data
+ * had been consumed. This covers the case when queue
+ * may have becomes starved between completion processing
+ * running and next time enqueue was scheduled.
+ *
+ * When queue is starved increase the limit by the amount
+ * of bytes both sent and completed in the last interval,
+ * plus any previous over-limit.
+ */
+ limit += POSDIFF(completed, dql->prev_num_queued) +
+ dql->prev_ovlimit;
+ dql->slack_start_time = jiffies;
+ dql->lowest_slack = UINT_MAX;
+ } else if (inprogress && prev_inprogress && !all_prev_completed) {
+ /*
+ * Queue was not starved, check if the limit can be decreased.
+ * A decrease is only considered if the queue has been busy in
+ * the whole interval (the check above).
+ *
+ * If there is slack, the amount of execess data queued above
+ * the the amount needed to prevent starvation, the queue limit
+ * can be decreased. To avoid hysteresis we consider the
+ * minimum amount of slack found over several iterations of the
+ * completion routine.
+ */
+ unsigned int slack, slack_last_objs;
+
+ /*
+ * Slack is the maximum of
+ * - The queue limit plus previous over-limit minus twice
+ * the number of objects completed. Note that two times
+ * number of completed bytes is a basis for an upper bound
+ * of the limit.
+ * - Portion of objects in the last queuing operation that
+ * was not part of non-zero previous over-limit. That is
+ * "round down" by non-overlimit portion of the last
+ * queueing operation.
+ */
+ slack = POSDIFF(limit + dql->prev_ovlimit,
+ 2 * (completed - dql->num_completed));
+ slack_last_objs = dql->prev_ovlimit ?
+ POSDIFF(dql->prev_last_obj_cnt, dql->prev_ovlimit) : 0;
+
+ slack = max(slack, slack_last_objs);
+
+ if (slack < dql->lowest_slack)
+ dql->lowest_slack = slack;
+
+ if (time_after(jiffies,
+ dql->slack_start_time + dql->slack_hold_time)) {
+ limit = POSDIFF(limit, dql->lowest_slack);
+ dql->slack_start_time = jiffies;
+ dql->lowest_slack = UINT_MAX;
+ }
+ }
+
+ /* Enforce bounds on limit */
+ limit = clamp(limit, dql->min_limit, dql->max_limit);
+
+ if (limit != dql->limit) {
+ dql->limit = limit;
+ ovlimit = 0;
+ }
+
+ dql->adj_limit = limit + completed;
+ dql->prev_ovlimit = ovlimit;
+ dql->prev_last_obj_cnt = dql->last_obj_cnt;
+ dql->num_completed = completed;
+ dql->prev_num_queued = dql->num_queued;
+}
+EXPORT_SYMBOL(dql_completed);
+
+void dql_reset(struct dql *dql)
+{
+ /* Reset all dynamic values */
+ dql->limit = 0;
+ dql->num_queued = 0;
+ dql->num_completed = 0;
+ dql->last_obj_cnt = 0;
+ dql->prev_num_queued = 0;
+ dql->prev_last_obj_cnt = 0;
+ dql->prev_ovlimit = 0;
+ dql->lowest_slack = UINT_MAX;
+ dql->slack_start_time = jiffies;
+}
+EXPORT_SYMBOL(dql_reset);
+
+int dql_init(struct dql *dql, unsigned hold_time)
+{
+ dql->max_limit = DQL_MAX_LIMIT;
+ dql->min_limit = 0;
+ dql->slack_hold_time = hold_time;
+ dql_reset(dql);
+ return 0;
+}
+EXPORT_SYMBOL(dql_init);