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Commit | Line | Data |
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2cb7cef9 BS |
1 | Subject: Add round_jiffies_up and related routines |
2 | From: Alan Stern <stern@rowland.harvard.edu> | |
3 | Date: Thu Nov 6 08:42:48 2008 +0100: | |
4 | Git: 9c133c469d38043d5aadaa03f2fb840d88d1cf4f | |
5 | References: bnc#464155 | |
6 | ||
7 | This patch (as1158b) adds round_jiffies_up() and friends. These | |
8 | routines work like the analogous round_jiffies() functions, except | |
9 | that they will never round down. | |
10 | ||
11 | The new routines will be useful for timeouts where we don't care | |
12 | exactly when the timer expires, provided it doesn't expire too soon. | |
13 | ||
14 | Signed-off-by: Alan Stern <stern@rowland.harvard.edu> | |
15 | Signed-off-by: Jens Axboe <jens.axboe@oracle.com> | |
16 | Signed-off-by: Hannes Reinecke <hare@suse.de> | |
17 | ||
18 | diff --git a/include/linux/timer.h b/include/linux/timer.h | |
19 | index d4ba792..daf9685 100644 | |
20 | --- a/include/linux/timer.h | |
21 | +++ b/include/linux/timer.h | |
22 | @@ -186,4 +186,9 @@ unsigned long __round_jiffies_relative(unsigned long j, int cpu); | |
23 | unsigned long round_jiffies(unsigned long j); | |
24 | unsigned long round_jiffies_relative(unsigned long j); | |
25 | ||
26 | +unsigned long __round_jiffies_up(unsigned long j, int cpu); | |
27 | +unsigned long __round_jiffies_up_relative(unsigned long j, int cpu); | |
28 | +unsigned long round_jiffies_up(unsigned long j); | |
29 | +unsigned long round_jiffies_up_relative(unsigned long j); | |
30 | + | |
31 | #endif | |
32 | diff --git a/kernel/timer.c b/kernel/timer.c | |
33 | index 56becf3..dbd50fa 100644 | |
34 | --- a/kernel/timer.c | |
35 | +++ b/kernel/timer.c | |
36 | @@ -112,27 +112,8 @@ timer_set_base(struct timer_list *timer, struct tvec_base *new_base) | |
37 | tbase_get_deferrable(timer->base)); | |
38 | } | |
39 | ||
40 | -/** | |
41 | - * __round_jiffies - function to round jiffies to a full second | |
42 | - * @j: the time in (absolute) jiffies that should be rounded | |
43 | - * @cpu: the processor number on which the timeout will happen | |
44 | - * | |
45 | - * __round_jiffies() rounds an absolute time in the future (in jiffies) | |
46 | - * up or down to (approximately) full seconds. This is useful for timers | |
47 | - * for which the exact time they fire does not matter too much, as long as | |
48 | - * they fire approximately every X seconds. | |
49 | - * | |
50 | - * By rounding these timers to whole seconds, all such timers will fire | |
51 | - * at the same time, rather than at various times spread out. The goal | |
52 | - * of this is to have the CPU wake up less, which saves power. | |
53 | - * | |
54 | - * The exact rounding is skewed for each processor to avoid all | |
55 | - * processors firing at the exact same time, which could lead | |
56 | - * to lock contention or spurious cache line bouncing. | |
57 | - * | |
58 | - * The return value is the rounded version of the @j parameter. | |
59 | - */ | |
60 | -unsigned long __round_jiffies(unsigned long j, int cpu) | |
61 | +static unsigned long round_jiffies_common(unsigned long j, int cpu, | |
62 | + bool force_up) | |
63 | { | |
64 | int rem; | |
65 | unsigned long original = j; | |
66 | @@ -154,8 +135,9 @@ unsigned long __round_jiffies(unsigned long j, int cpu) | |
67 | * due to delays of the timer irq, long irq off times etc etc) then | |
68 | * we should round down to the whole second, not up. Use 1/4th second | |
69 | * as cutoff for this rounding as an extreme upper bound for this. | |
70 | + * But never round down if @force_up is set. | |
71 | */ | |
72 | - if (rem < HZ/4) /* round down */ | |
73 | + if (rem < HZ/4 && !force_up) /* round down */ | |
74 | j = j - rem; | |
75 | else /* round up */ | |
76 | j = j - rem + HZ; | |
77 | @@ -167,6 +149,31 @@ unsigned long __round_jiffies(unsigned long j, int cpu) | |
78 | return original; | |
79 | return j; | |
80 | } | |
81 | + | |
82 | +/** | |
83 | + * __round_jiffies - function to round jiffies to a full second | |
84 | + * @j: the time in (absolute) jiffies that should be rounded | |
85 | + * @cpu: the processor number on which the timeout will happen | |
86 | + * | |
87 | + * __round_jiffies() rounds an absolute time in the future (in jiffies) | |
88 | + * up or down to (approximately) full seconds. This is useful for timers | |
89 | + * for which the exact time they fire does not matter too much, as long as | |
90 | + * they fire approximately every X seconds. | |
91 | + * | |
92 | + * By rounding these timers to whole seconds, all such timers will fire | |
93 | + * at the same time, rather than at various times spread out. The goal | |
94 | + * of this is to have the CPU wake up less, which saves power. | |
95 | + * | |
96 | + * The exact rounding is skewed for each processor to avoid all | |
97 | + * processors firing at the exact same time, which could lead | |
98 | + * to lock contention or spurious cache line bouncing. | |
99 | + * | |
100 | + * The return value is the rounded version of the @j parameter. | |
101 | + */ | |
102 | +unsigned long __round_jiffies(unsigned long j, int cpu) | |
103 | +{ | |
104 | + return round_jiffies_common(j, cpu, false); | |
105 | +} | |
106 | EXPORT_SYMBOL_GPL(__round_jiffies); | |
107 | ||
108 | /** | |
109 | @@ -191,13 +198,10 @@ EXPORT_SYMBOL_GPL(__round_jiffies); | |
110 | */ | |
111 | unsigned long __round_jiffies_relative(unsigned long j, int cpu) | |
112 | { | |
113 | - /* | |
114 | - * In theory the following code can skip a jiffy in case jiffies | |
115 | - * increments right between the addition and the later subtraction. | |
116 | - * However since the entire point of this function is to use approximate | |
117 | - * timeouts, it's entirely ok to not handle that. | |
118 | - */ | |
119 | - return __round_jiffies(j + jiffies, cpu) - jiffies; | |
120 | + unsigned long j0 = jiffies; | |
121 | + | |
122 | + /* Use j0 because jiffies might change while we run */ | |
123 | + return round_jiffies_common(j + j0, cpu, false) - j0; | |
124 | } | |
125 | EXPORT_SYMBOL_GPL(__round_jiffies_relative); | |
126 | ||
127 | @@ -218,7 +222,7 @@ EXPORT_SYMBOL_GPL(__round_jiffies_relative); | |
128 | */ | |
129 | unsigned long round_jiffies(unsigned long j) | |
130 | { | |
131 | - return __round_jiffies(j, raw_smp_processor_id()); | |
132 | + return round_jiffies_common(j, raw_smp_processor_id(), false); | |
133 | } | |
134 | EXPORT_SYMBOL_GPL(round_jiffies); | |
135 | ||
136 | @@ -243,6 +247,71 @@ unsigned long round_jiffies_relative(unsigned long j) | |
137 | } | |
138 | EXPORT_SYMBOL_GPL(round_jiffies_relative); | |
139 | ||
140 | +/** | |
141 | + * __round_jiffies_up - function to round jiffies up to a full second | |
142 | + * @j: the time in (absolute) jiffies that should be rounded | |
143 | + * @cpu: the processor number on which the timeout will happen | |
144 | + * | |
145 | + * This is the same as __round_jiffies() except that it will never | |
146 | + * round down. This is useful for timeouts for which the exact time | |
147 | + * of firing does not matter too much, as long as they don't fire too | |
148 | + * early. | |
149 | + */ | |
150 | +unsigned long __round_jiffies_up(unsigned long j, int cpu) | |
151 | +{ | |
152 | + return round_jiffies_common(j, cpu, true); | |
153 | +} | |
154 | +EXPORT_SYMBOL_GPL(__round_jiffies_up); | |
155 | + | |
156 | +/** | |
157 | + * __round_jiffies_up_relative - function to round jiffies up to a full second | |
158 | + * @j: the time in (relative) jiffies that should be rounded | |
159 | + * @cpu: the processor number on which the timeout will happen | |
160 | + * | |
161 | + * This is the same as __round_jiffies_relative() except that it will never | |
162 | + * round down. This is useful for timeouts for which the exact time | |
163 | + * of firing does not matter too much, as long as they don't fire too | |
164 | + * early. | |
165 | + */ | |
166 | +unsigned long __round_jiffies_up_relative(unsigned long j, int cpu) | |
167 | +{ | |
168 | + unsigned long j0 = jiffies; | |
169 | + | |
170 | + /* Use j0 because jiffies might change while we run */ | |
171 | + return round_jiffies_common(j + j0, cpu, true) - j0; | |
172 | +} | |
173 | +EXPORT_SYMBOL_GPL(__round_jiffies_up_relative); | |
174 | + | |
175 | +/** | |
176 | + * round_jiffies_up - function to round jiffies up to a full second | |
177 | + * @j: the time in (absolute) jiffies that should be rounded | |
178 | + * | |
179 | + * This is the same as round_jiffies() except that it will never | |
180 | + * round down. This is useful for timeouts for which the exact time | |
181 | + * of firing does not matter too much, as long as they don't fire too | |
182 | + * early. | |
183 | + */ | |
184 | +unsigned long round_jiffies_up(unsigned long j) | |
185 | +{ | |
186 | + return round_jiffies_common(j, raw_smp_processor_id(), true); | |
187 | +} | |
188 | +EXPORT_SYMBOL_GPL(round_jiffies_up); | |
189 | + | |
190 | +/** | |
191 | + * round_jiffies_up_relative - function to round jiffies up to a full second | |
192 | + * @j: the time in (relative) jiffies that should be rounded | |
193 | + * | |
194 | + * This is the same as round_jiffies_relative() except that it will never | |
195 | + * round down. This is useful for timeouts for which the exact time | |
196 | + * of firing does not matter too much, as long as they don't fire too | |
197 | + * early. | |
198 | + */ | |
199 | +unsigned long round_jiffies_up_relative(unsigned long j) | |
200 | +{ | |
201 | + return __round_jiffies_up_relative(j, raw_smp_processor_id()); | |
202 | +} | |
203 | +EXPORT_SYMBOL_GPL(round_jiffies_up_relative); | |
204 | + | |
205 | ||
206 | static inline void set_running_timer(struct tvec_base *base, | |
207 | struct timer_list *timer) |