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Greg Kroah-Hartmanb2441312017-11-01 15:07:57 +01001// SPDX-License-Identifier: GPL-2.0
Tom Herbert75957ba2011-11-28 16:32:35 +00002/*
3 * Dynamic byte queue limits. See include/linux/dynamic_queue_limits.h
4 *
5 * Copyright (c) 2011, Tom Herbert <therbert@google.com>
6 */
Tom Herbert75957ba2011-11-28 16:32:35 +00007#include <linux/types.h>
Tom Herbert75957ba2011-11-28 16:32:35 +00008#include <linux/kernel.h>
Tom Herbert930c5142012-03-11 19:59:43 -07009#include <linux/jiffies.h>
Tom Herbert75957ba2011-11-28 16:32:35 +000010#include <linux/dynamic_queue_limits.h>
Rasmus Villemoes565ac232015-02-12 15:02:37 -080011#include <linux/compiler.h>
12#include <linux/export.h>
Tom Herbert75957ba2011-11-28 16:32:35 +000013
Hiroaki SHIMODA0cfd32b2012-05-30 12:24:39 +000014#define POSDIFF(A, B) ((int)((A) - (B)) > 0 ? (A) - (B) : 0)
Hiroaki SHIMODA25426b72012-05-30 12:25:19 +000015#define AFTER_EQ(A, B) ((int)((A) - (B)) >= 0)
Tom Herbert75957ba2011-11-28 16:32:35 +000016
17/* Records completed count and recalculates the queue limit */
18void dql_completed(struct dql *dql, unsigned int count)
19{
20 unsigned int inprogress, prev_inprogress, limit;
Hiroaki SHIMODA914bec12012-05-30 12:25:37 +000021 unsigned int ovlimit, completed, num_queued;
Hiroaki SHIMODA25426b72012-05-30 12:25:19 +000022 bool all_prev_completed;
Tom Herbert75957ba2011-11-28 16:32:35 +000023
Mark Rutland6aa7de02017-10-23 14:07:29 -070024 num_queued = READ_ONCE(dql->num_queued);
Hiroaki SHIMODA914bec12012-05-30 12:25:37 +000025
Tom Herbert75957ba2011-11-28 16:32:35 +000026 /* Can't complete more than what's in queue */
Hiroaki SHIMODA914bec12012-05-30 12:25:37 +000027 BUG_ON(count > num_queued - dql->num_completed);
Tom Herbert75957ba2011-11-28 16:32:35 +000028
29 completed = dql->num_completed + count;
30 limit = dql->limit;
Hiroaki SHIMODA914bec12012-05-30 12:25:37 +000031 ovlimit = POSDIFF(num_queued - dql->num_completed, limit);
32 inprogress = num_queued - completed;
Tom Herbert75957ba2011-11-28 16:32:35 +000033 prev_inprogress = dql->prev_num_queued - dql->num_completed;
Hiroaki SHIMODA25426b72012-05-30 12:25:19 +000034 all_prev_completed = AFTER_EQ(completed, dql->prev_num_queued);
Tom Herbert75957ba2011-11-28 16:32:35 +000035
36 if ((ovlimit && !inprogress) ||
37 (dql->prev_ovlimit && all_prev_completed)) {
38 /*
39 * Queue considered starved if:
40 * - The queue was over-limit in the last interval,
41 * and there is no more data in the queue.
42 * OR
43 * - The queue was over-limit in the previous interval and
44 * when enqueuing it was possible that all queued data
45 * had been consumed. This covers the case when queue
46 * may have becomes starved between completion processing
47 * running and next time enqueue was scheduled.
48 *
49 * When queue is starved increase the limit by the amount
50 * of bytes both sent and completed in the last interval,
51 * plus any previous over-limit.
52 */
53 limit += POSDIFF(completed, dql->prev_num_queued) +
54 dql->prev_ovlimit;
55 dql->slack_start_time = jiffies;
56 dql->lowest_slack = UINT_MAX;
57 } else if (inprogress && prev_inprogress && !all_prev_completed) {
58 /*
59 * Queue was not starved, check if the limit can be decreased.
60 * A decrease is only considered if the queue has been busy in
61 * the whole interval (the check above).
62 *
63 * If there is slack, the amount of execess data queued above
64 * the the amount needed to prevent starvation, the queue limit
65 * can be decreased. To avoid hysteresis we consider the
66 * minimum amount of slack found over several iterations of the
67 * completion routine.
68 */
69 unsigned int slack, slack_last_objs;
70
71 /*
72 * Slack is the maximum of
73 * - The queue limit plus previous over-limit minus twice
74 * the number of objects completed. Note that two times
75 * number of completed bytes is a basis for an upper bound
76 * of the limit.
77 * - Portion of objects in the last queuing operation that
78 * was not part of non-zero previous over-limit. That is
79 * "round down" by non-overlimit portion of the last
80 * queueing operation.
81 */
82 slack = POSDIFF(limit + dql->prev_ovlimit,
83 2 * (completed - dql->num_completed));
84 slack_last_objs = dql->prev_ovlimit ?
85 POSDIFF(dql->prev_last_obj_cnt, dql->prev_ovlimit) : 0;
86
87 slack = max(slack, slack_last_objs);
88
89 if (slack < dql->lowest_slack)
90 dql->lowest_slack = slack;
91
92 if (time_after(jiffies,
93 dql->slack_start_time + dql->slack_hold_time)) {
94 limit = POSDIFF(limit, dql->lowest_slack);
95 dql->slack_start_time = jiffies;
96 dql->lowest_slack = UINT_MAX;
97 }
98 }
99
100 /* Enforce bounds on limit */
101 limit = clamp(limit, dql->min_limit, dql->max_limit);
102
103 if (limit != dql->limit) {
104 dql->limit = limit;
105 ovlimit = 0;
106 }
107
108 dql->adj_limit = limit + completed;
109 dql->prev_ovlimit = ovlimit;
110 dql->prev_last_obj_cnt = dql->last_obj_cnt;
111 dql->num_completed = completed;
Hiroaki SHIMODA914bec12012-05-30 12:25:37 +0000112 dql->prev_num_queued = num_queued;
Tom Herbert75957ba2011-11-28 16:32:35 +0000113}
114EXPORT_SYMBOL(dql_completed);
115
116void dql_reset(struct dql *dql)
117{
118 /* Reset all dynamic values */
119 dql->limit = 0;
120 dql->num_queued = 0;
121 dql->num_completed = 0;
122 dql->last_obj_cnt = 0;
123 dql->prev_num_queued = 0;
124 dql->prev_last_obj_cnt = 0;
125 dql->prev_ovlimit = 0;
126 dql->lowest_slack = UINT_MAX;
127 dql->slack_start_time = jiffies;
128}
129EXPORT_SYMBOL(dql_reset);
130
Stephen Hemminger7a0947e2017-10-17 17:16:52 -0700131void dql_init(struct dql *dql, unsigned int hold_time)
Tom Herbert75957ba2011-11-28 16:32:35 +0000132{
133 dql->max_limit = DQL_MAX_LIMIT;
134 dql->min_limit = 0;
135 dql->slack_hold_time = hold_time;
136 dql_reset(dql);
Tom Herbert75957ba2011-11-28 16:32:35 +0000137}
138EXPORT_SYMBOL(dql_init);