1 files changed, 133 insertions, 0 deletions

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);