1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
|
// SPDX-License-Identifier: GPL-2.0
/*
* Dynamic byte queue limits. See include/linux/dynamic_queue_limits.h
*
* Copyright (c) 2011, Tom Herbert <therbert@google.com>
*/
#include <linux/types.h>
#include <linux/kernel.h>
#include <linux/jiffies.h>
#include <linux/dynamic_queue_limits.h>
#include <linux/compiler.h>
#include <linux/export.h>
#include <trace/events/napi.h>
#define POSDIFF(A, B) ((int)((A) - (B)) > 0 ? (A) - (B) : 0)
#define AFTER_EQ(A, B) ((int)((A) - (B)) >= 0)
static void dql_check_stall(struct dql *dql, unsigned short stall_thrs)
{
unsigned long now;
if (!stall_thrs)
return;
now = jiffies;
/* Check for a potential stall */
if (time_after_eq(now, dql->last_reap + stall_thrs)) {
unsigned long hist_head, t, start, end;
/* We are trying to detect a period of at least @stall_thrs
* jiffies without any Tx completions, but during first half
* of which some Tx was posted.
*/
dqs_again:
hist_head = READ_ONCE(dql->history_head);
/* pairs with smp_wmb() in dql_queued() */
smp_rmb();
/* Get the previous entry in the ring buffer, which is the
* oldest sample.
*/
start = (hist_head - DQL_HIST_LEN + 1) * BITS_PER_LONG;
/* Advance start to continue from the last reap time */
if (time_before(start, dql->last_reap + 1))
start = dql->last_reap + 1;
/* Newest sample we should have already seen a completion for */
end = hist_head * BITS_PER_LONG + (BITS_PER_LONG - 1);
/* Shrink the search space to [start, (now - start_thrs/2)] if
* `end` is beyond the stall zone
*/
if (time_before(now, end + stall_thrs / 2))
end = now - stall_thrs / 2;
/* Search for the queued time in [t, end] */
for (t = start; time_before_eq(t, end); t++)
if (test_bit(t % (DQL_HIST_LEN * BITS_PER_LONG),
dql->history))
break;
/* Variable t contains the time of the queue */
if (!time_before_eq(t, end))
goto no_stall;
/* The ring buffer was modified in the meantime, retry */
if (hist_head != READ_ONCE(dql->history_head))
goto dqs_again;
dql->stall_cnt++;
dql->stall_max = max_t(unsigned short, dql->stall_max, now - t);
trace_dql_stall_detected(dql->stall_thrs, now - t,
dql->last_reap, dql->history_head,
now, dql->history);
}
no_stall:
dql->last_reap = now;
}
/* 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, completed, num_queued;
unsigned short stall_thrs;
bool all_prev_completed;
num_queued = READ_ONCE(dql->num_queued);
/* Read stall_thrs in advance since it belongs to the same (first)
* cache line as ->num_queued. This way, dql_check_stall() does not
* need to touch the first cache line again later, reducing the window
* of possible false sharing.
*/
stall_thrs = READ_ONCE(dql->stall_thrs);
/* Can't complete more than what's in queue */
BUG_ON(count > num_queued - dql->num_completed);
completed = dql->num_completed + count;
limit = dql->limit;
ovlimit = POSDIFF(num_queued - dql->num_completed, limit);
inprogress = num_queued - completed;
prev_inprogress = dql->prev_num_queued - dql->num_completed;
all_prev_completed = AFTER_EQ(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 excess data queued above
* 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 = READ_ONCE(dql->last_obj_cnt);
dql->num_completed = completed;
dql->prev_num_queued = num_queued;
dql_check_stall(dql, stall_thrs);
}
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;
dql->last_reap = jiffies;
dql->history_head = jiffies / BITS_PER_LONG;
memset(dql->history, 0, sizeof(dql->history));
}
EXPORT_SYMBOL(dql_reset);
void dql_init(struct dql *dql, unsigned int hold_time)
{
dql->max_limit = DQL_MAX_LIMIT;
dql->min_limit = 0;
dql->slack_hold_time = hold_time;
dql->stall_thrs = 0;
dql_reset(dql);
}
EXPORT_SYMBOL(dql_init);
|
