Merge tag 'sched-urgent-2020-11-15' of git://git.kernel.org/pub/scm/linux/kernel...
[platform/kernel/linux-rpi.git] / lib / dynamic_queue_limits.c
1 // SPDX-License-Identifier: GPL-2.0
2 /*
3  * Dynamic byte queue limits.  See include/linux/dynamic_queue_limits.h
4  *
5  * Copyright (c) 2011, Tom Herbert <therbert@google.com>
6  */
7 #include <linux/types.h>
8 #include <linux/kernel.h>
9 #include <linux/jiffies.h>
10 #include <linux/dynamic_queue_limits.h>
11 #include <linux/compiler.h>
12 #include <linux/export.h>
13
14 #define POSDIFF(A, B) ((int)((A) - (B)) > 0 ? (A) - (B) : 0)
15 #define AFTER_EQ(A, B) ((int)((A) - (B)) >= 0)
16
17 /* Records completed count and recalculates the queue limit */
18 void dql_completed(struct dql *dql, unsigned int count)
19 {
20         unsigned int inprogress, prev_inprogress, limit;
21         unsigned int ovlimit, completed, num_queued;
22         bool all_prev_completed;
23
24         num_queued = READ_ONCE(dql->num_queued);
25
26         /* Can't complete more than what's in queue */
27         BUG_ON(count > num_queued - dql->num_completed);
28
29         completed = dql->num_completed + count;
30         limit = dql->limit;
31         ovlimit = POSDIFF(num_queued - dql->num_completed, limit);
32         inprogress = num_queued - completed;
33         prev_inprogress = dql->prev_num_queued - dql->num_completed;
34         all_prev_completed = AFTER_EQ(completed, dql->prev_num_queued);
35
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 excess data queued above
64                  * 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;
112         dql->prev_num_queued = num_queued;
113 }
114 EXPORT_SYMBOL(dql_completed);
115
116 void 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 }
129 EXPORT_SYMBOL(dql_reset);
130
131 void dql_init(struct dql *dql, unsigned int hold_time)
132 {
133         dql->max_limit = DQL_MAX_LIMIT;
134         dql->min_limit = 0;
135         dql->slack_hold_time = hold_time;
136         dql_reset(dql);
137 }
138 EXPORT_SYMBOL(dql_init);