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b2441318 | 1 | /* SPDX-License-Identifier: GPL-2.0 */ |
75957ba3 TH |
2 | /* |
3 | * Dynamic queue limits (dql) - Definitions | |
4 | * | |
5 | * Copyright (c) 2011, Tom Herbert <therbert@google.com> | |
6 | * | |
7 | * This header file contains the definitions for dynamic queue limits (dql). | |
8 | * dql would be used in conjunction with a producer/consumer type queue | |
9 | * (possibly a HW queue). Such a queue would have these general properties: | |
10 | * | |
11 | * 1) Objects are queued up to some limit specified as number of objects. | |
12 | * 2) Periodically a completion process executes which retires consumed | |
13 | * objects. | |
14 | * 3) Starvation occurs when limit has been reached, all queued data has | |
15 | * actually been consumed, but completion processing has not yet run | |
16 | * so queuing new data is blocked. | |
17 | * 4) Minimizing the amount of queued data is desirable. | |
18 | * | |
19 | * The goal of dql is to calculate the limit as the minimum number of objects | |
20 | * needed to prevent starvation. | |
21 | * | |
22 | * The primary functions of dql are: | |
23 | * dql_queued - called when objects are enqueued to record number of objects | |
24 | * dql_avail - returns how many objects are available to be queued based | |
25 | * on the object limit and how many objects are already enqueued | |
26 | * dql_completed - called at completion time to indicate how many objects | |
27 | * were retired from the queue | |
28 | * | |
29 | * The dql implementation does not implement any locking for the dql data | |
30 | * structures, the higher layer should provide this. dql_queued should | |
31 | * be serialized to prevent concurrent execution of the function; this | |
32 | * is also true for dql_completed. However, dql_queued and dlq_completed can | |
33 | * be executed concurrently (i.e. they can be protected by different locks). | |
34 | */ | |
35 | ||
36 | #ifndef _LINUX_DQL_H | |
37 | #define _LINUX_DQL_H | |
38 | ||
39 | #ifdef __KERNEL__ | |
40 | ||
6025b913 | 41 | #include <linux/bitops.h> |
0cd39f46 PZ |
42 | #include <asm/bug.h> |
43 | ||
6025b913 JK |
44 | #define DQL_HIST_LEN 4 |
45 | #define DQL_HIST_ENT(dql, idx) ((dql)->history[(idx) % DQL_HIST_LEN]) | |
46 | ||
75957ba3 TH |
47 | struct dql { |
48 | /* Fields accessed in enqueue path (dql_queued) */ | |
49 | unsigned int num_queued; /* Total ever queued */ | |
50 | unsigned int adj_limit; /* limit + num_completed */ | |
51 | unsigned int last_obj_cnt; /* Count at last queuing */ | |
52 | ||
4ba67ef3 BL |
53 | /* Stall threshold (in jiffies), defined by user */ |
54 | unsigned short stall_thrs; | |
55 | ||
6025b913 JK |
56 | unsigned long history_head; /* top 58 bits of jiffies */ |
57 | /* stall entries, a bit per entry */ | |
58 | unsigned long history[DQL_HIST_LEN]; | |
59 | ||
75957ba3 TH |
60 | /* Fields accessed only by completion path (dql_completed) */ |
61 | ||
62 | unsigned int limit ____cacheline_aligned_in_smp; /* Current limit */ | |
63 | unsigned int num_completed; /* Total ever completed */ | |
64 | ||
65 | unsigned int prev_ovlimit; /* Previous over limit */ | |
66 | unsigned int prev_num_queued; /* Previous queue total */ | |
67 | unsigned int prev_last_obj_cnt; /* Previous queuing cnt */ | |
68 | ||
69 | unsigned int lowest_slack; /* Lowest slack found */ | |
70 | unsigned long slack_start_time; /* Time slacks seen */ | |
71 | ||
72 | /* Configuration */ | |
73 | unsigned int max_limit; /* Max limit */ | |
74 | unsigned int min_limit; /* Minimum limit */ | |
75 | unsigned int slack_hold_time; /* Time to measure slack */ | |
6025b913 | 76 | |
6025b913 JK |
77 | /* Longest stall detected, reported to user */ |
78 | unsigned short stall_max; | |
79 | unsigned long last_reap; /* Last reap (in jiffies) */ | |
80 | unsigned long stall_cnt; /* Number of stalls */ | |
75957ba3 TH |
81 | }; |
82 | ||
83 | /* Set some static maximums */ | |
84 | #define DQL_MAX_OBJECT (UINT_MAX / 16) | |
85 | #define DQL_MAX_LIMIT ((UINT_MAX / 2) - DQL_MAX_OBJECT) | |
86 | ||
cbe481a1 BL |
87 | /* Populate the bitmap to be processed later in dql_check_stall() */ |
88 | static inline void dql_queue_stall(struct dql *dql) | |
75957ba3 | 89 | { |
6025b913 JK |
90 | unsigned long map, now, now_hi, i; |
91 | ||
6025b913 JK |
92 | now = jiffies; |
93 | now_hi = now / BITS_PER_LONG; | |
94 | ||
95 | /* The following code set a bit in the ring buffer, where each | |
96 | * bit trackes time the packet was queued. The dql->history buffer | |
97 | * tracks DQL_HIST_LEN * BITS_PER_LONG time (jiffies) slot | |
98 | */ | |
99 | if (unlikely(now_hi != dql->history_head)) { | |
100 | /* About to reuse slots, clear them */ | |
101 | for (i = 0; i < DQL_HIST_LEN; i++) { | |
102 | /* Multiplication masks high bits */ | |
103 | if (now_hi * BITS_PER_LONG == | |
104 | (dql->history_head + i) * BITS_PER_LONG) | |
105 | break; | |
106 | DQL_HIST_ENT(dql, dql->history_head + i + 1) = 0; | |
107 | } | |
108 | /* pairs with smp_rmb() in dql_check_stall() */ | |
109 | smp_wmb(); | |
110 | WRITE_ONCE(dql->history_head, now_hi); | |
111 | } | |
112 | ||
113 | /* __set_bit() does not guarantee WRITE_ONCE() semantics */ | |
114 | map = DQL_HIST_ENT(dql, now_hi); | |
115 | ||
116 | /* Populate the history with an entry (bit) per queued */ | |
117 | if (!(map & BIT_MASK(now))) | |
118 | WRITE_ONCE(DQL_HIST_ENT(dql, now_hi), map | BIT_MASK(now)); | |
75957ba3 TH |
119 | } |
120 | ||
cbe481a1 BL |
121 | /* |
122 | * Record number of objects queued. Assumes that caller has already checked | |
123 | * availability in the queue with dql_avail. | |
124 | */ | |
125 | static inline void dql_queued(struct dql *dql, unsigned int count) | |
126 | { | |
127 | if (WARN_ON_ONCE(count > DQL_MAX_OBJECT)) | |
128 | return; | |
129 | ||
130 | dql->last_obj_cnt = count; | |
131 | ||
132 | /* We want to force a write first, so that cpu do not attempt | |
133 | * to get cache line containing last_obj_cnt, num_queued, adj_limit | |
134 | * in Shared state, but directly does a Request For Ownership | |
135 | * It is only a hint, we use barrier() only. | |
136 | */ | |
137 | barrier(); | |
138 | ||
139 | dql->num_queued += count; | |
140 | ||
721f076b BL |
141 | /* Only populate stall information if the threshold is set */ |
142 | if (READ_ONCE(dql->stall_thrs)) | |
143 | dql_queue_stall(dql); | |
cbe481a1 BL |
144 | } |
145 | ||
75957ba3 TH |
146 | /* Returns how many objects can be queued, < 0 indicates over limit. */ |
147 | static inline int dql_avail(const struct dql *dql) | |
148 | { | |
6aa7de05 | 149 | return READ_ONCE(dql->adj_limit) - READ_ONCE(dql->num_queued); |
75957ba3 TH |
150 | } |
151 | ||
152 | /* Record number of completed objects and recalculate the limit. */ | |
153 | void dql_completed(struct dql *dql, unsigned int count); | |
154 | ||
155 | /* Reset dql state */ | |
156 | void dql_reset(struct dql *dql); | |
157 | ||
158 | /* Initialize dql state */ | |
7a0947e7 | 159 | void dql_init(struct dql *dql, unsigned int hold_time); |
75957ba3 TH |
160 | |
161 | #endif /* _KERNEL_ */ | |
162 | ||
163 | #endif /* _LINUX_DQL_H */ |