Root/lib/dynamic_queue_limits.c

Source at commit b386be689295730688885552666ea40b2e639b14 created 8 years 11 months ago.
By Maarten ter Huurne, Revert "MIPS: JZ4740: reset: Initialize hibernate wakeup counters."
1/*
2 * Dynamic byte queue limits. See include/linux/dynamic_queue_limits.h
3 *
4 * Copyright (c) 2011, Tom Herbert <therbert@google.com>
5 */
6#include <linux/module.h>
7#include <linux/types.h>
8#include <linux/ctype.h>
9#include <linux/kernel.h>
10#include <linux/jiffies.h>
11#include <linux/dynamic_queue_limits.h>
12
13#define POSDIFF(A, B) ((A) > (B) ? (A) - (B) : 0)
14
15/* Records completed count and recalculates the queue limit */
16void dql_completed(struct dql *dql, unsigned int count)
17{
18    unsigned int inprogress, prev_inprogress, limit;
19    unsigned int ovlimit, all_prev_completed, completed;
20
21    /* Can't complete more than what's in queue */
22    BUG_ON(count > dql->num_queued - dql->num_completed);
23
24    completed = dql->num_completed + count;
25    limit = dql->limit;
26    ovlimit = POSDIFF(dql->num_queued - dql->num_completed, limit);
27    inprogress = dql->num_queued - completed;
28    prev_inprogress = dql->prev_num_queued - dql->num_completed;
29    all_prev_completed = POSDIFF(completed, dql->prev_num_queued);
30
31    if ((ovlimit && !inprogress) ||
32        (dql->prev_ovlimit && all_prev_completed)) {
33        /*
34         * Queue considered starved if:
35         * - The queue was over-limit in the last interval,
36         * and there is no more data in the queue.
37         * OR
38         * - The queue was over-limit in the previous interval and
39         * when enqueuing it was possible that all queued data
40         * had been consumed. This covers the case when queue
41         * may have becomes starved between completion processing
42         * running and next time enqueue was scheduled.
43         *
44         * When queue is starved increase the limit by the amount
45         * of bytes both sent and completed in the last interval,
46         * plus any previous over-limit.
47         */
48        limit += POSDIFF(completed, dql->prev_num_queued) +
49             dql->prev_ovlimit;
50        dql->slack_start_time = jiffies;
51        dql->lowest_slack = UINT_MAX;
52    } else if (inprogress && prev_inprogress && !all_prev_completed) {
53        /*
54         * Queue was not starved, check if the limit can be decreased.
55         * A decrease is only considered if the queue has been busy in
56         * the whole interval (the check above).
57         *
58         * If there is slack, the amount of execess data queued above
59         * the the amount needed to prevent starvation, the queue limit
60         * can be decreased. To avoid hysteresis we consider the
61         * minimum amount of slack found over several iterations of the
62         * completion routine.
63         */
64        unsigned int slack, slack_last_objs;
65
66        /*
67         * Slack is the maximum of
68         * - The queue limit plus previous over-limit minus twice
69         * the number of objects completed. Note that two times
70         * number of completed bytes is a basis for an upper bound
71         * of the limit.
72         * - Portion of objects in the last queuing operation that
73         * was not part of non-zero previous over-limit. That is
74         * "round down" by non-overlimit portion of the last
75         * queueing operation.
76         */
77        slack = POSDIFF(limit + dql->prev_ovlimit,
78            2 * (completed - dql->num_completed));
79        slack_last_objs = dql->prev_ovlimit ?
80            POSDIFF(dql->prev_last_obj_cnt, dql->prev_ovlimit) : 0;
81
82        slack = max(slack, slack_last_objs);
83
84        if (slack < dql->lowest_slack)
85            dql->lowest_slack = slack;
86
87        if (time_after(jiffies,
88                   dql->slack_start_time + dql->slack_hold_time)) {
89            limit = POSDIFF(limit, dql->lowest_slack);
90            dql->slack_start_time = jiffies;
91            dql->lowest_slack = UINT_MAX;
92        }
93    }
94
95    /* Enforce bounds on limit */
96    limit = clamp(limit, dql->min_limit, dql->max_limit);
97
98    if (limit != dql->limit) {
99        dql->limit = limit;
100        ovlimit = 0;
101    }
102
103    dql->adj_limit = limit + completed;
104    dql->prev_ovlimit = ovlimit;
105    dql->prev_last_obj_cnt = dql->last_obj_cnt;
106    dql->num_completed = completed;
107    dql->prev_num_queued = dql->num_queued;
108}
109EXPORT_SYMBOL(dql_completed);
110
111void dql_reset(struct dql *dql)
112{
113    /* Reset all dynamic values */
114    dql->limit = 0;
115    dql->num_queued = 0;
116    dql->num_completed = 0;
117    dql->last_obj_cnt = 0;
118    dql->prev_num_queued = 0;
119    dql->prev_last_obj_cnt = 0;
120    dql->prev_ovlimit = 0;
121    dql->lowest_slack = UINT_MAX;
122    dql->slack_start_time = jiffies;
123}
124EXPORT_SYMBOL(dql_reset);
125
126int dql_init(struct dql *dql, unsigned hold_time)
127{
128    dql->max_limit = DQL_MAX_LIMIT;
129    dql->min_limit = 0;
130    dql->slack_hold_time = hold_time;
131    dql_reset(dql);
132    return 0;
133}
134EXPORT_SYMBOL(dql_init);
135

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