1 #ifndef _LINUX_JIFFIES_H 2 #define _LINUX_JIFFIES_H 3 4 #include <linux/calc64.h> 5 #include <linux/kernel.h> 6 #include <linux/types.h> 7 #include <linux/time.h> 8 #include <linux/timex.h> 9 #include <asm/param.h> /* for HZ */ 10 11 /* 12 * The following defines establish the engineering parameters of the PLL 13 * model. The HZ variable establishes the timer interrupt frequency, 100 Hz 14 * for the SunOS kernel, 256 Hz for the Ultrix kernel and 1024 Hz for the 15 * OSF/1 kernel. The SHIFT_HZ define expresses the same value as the 16 * nearest power of two in order to avoid hardware multiply operations. 17 */ 18 #if HZ >= 12 && HZ < 24 19 # define SHIFT_HZ 4 20 #elif HZ >= 24 && HZ < 48 21 # define SHIFT_HZ 5 22 #elif HZ >= 48 && HZ < 96 23 # define SHIFT_HZ 6 24 #elif HZ >= 96 && HZ < 192 25 # define SHIFT_HZ 7 26 #elif HZ >= 192 && HZ < 384 27 # define SHIFT_HZ 8 28 #elif HZ >= 384 && HZ < 768 29 # define SHIFT_HZ 9 30 #elif HZ >= 768 && HZ < 1536 31 # define SHIFT_HZ 10 32 #else 33 # error You lose. 34 #endif 35 36 /* LATCH is used in the interval timer and ftape setup. */ 37 #define LATCH ((CLOCK_TICK_RATE + HZ/2) / HZ) /* For divider */ 38 39 #define LATCH_HPET ((HPET_TICK_RATE + HZ/2) / HZ) 40 41 /* Suppose we want to devide two numbers NOM and DEN: NOM/DEN, the we can 42 * improve accuracy by shifting LSH bits, hence calculating: 43 * (NOM << LSH) / DEN 44 * This however means trouble for large NOM, because (NOM << LSH) may no 45 * longer fit in 32 bits. The following way of calculating this gives us 46 * some slack, under the following conditions: 47 * - (NOM / DEN) fits in (32 - LSH) bits. 48 * - (NOM % DEN) fits in (32 - LSH) bits. 49 */ 50 #define SH_DIV(NOM,DEN,LSH) ( (((NOM) / (DEN)) << (LSH)) \ 51 + ((((NOM) % (DEN)) << (LSH)) + (DEN) / 2) / (DEN)) 52 53 /* HZ is the requested value. ACTHZ is actual HZ ("<< 8" is for accuracy) */ 54 #define ACTHZ (SH_DIV (CLOCK_TICK_RATE, LATCH, 8)) 55 56 #define ACTHZ_HPET (SH_DIV (HPET_TICK_RATE, LATCH_HPET, 8)) 57 58 /* TICK_NSEC is the time between ticks in nsec assuming real ACTHZ */ 59 #define TICK_NSEC (SH_DIV (1000000UL * 1000, ACTHZ, 8)) 60 61 #define TICK_NSEC_HPET (SH_DIV(1000000UL * 1000, ACTHZ_HPET, 8)) 62 63 /* TICK_USEC is the time between ticks in usec assuming fake USER_HZ */ 64 #define TICK_USEC ((1000000UL + USER_HZ/2) / USER_HZ) 65 66 /* TICK_USEC_TO_NSEC is the time between ticks in nsec assuming real ACTHZ and */ 67 /* a value TUSEC for TICK_USEC (can be set bij adjtimex) */ 68 #define TICK_USEC_TO_NSEC(TUSEC) (SH_DIV (TUSEC * USER_HZ * 1000, ACTHZ, 8)) 69 70 /* some arch's have a small-data section that can be accessed register-relative 71 * but that can only take up to, say, 4-byte variables. jiffies being part of 72 * an 8-byte variable may not be correctly accessed unless we force the issue 73 */ 74 #define __jiffy_data __attribute__((section(".data"))) 75 76 /* 77 * The 64-bit value is not atomic - you MUST NOT read it 78 * without sampling the sequence number in xtime_lock. 79 * get_jiffies_64() will do this for you as appropriate. 80 */ 81 extern u64 __jiffy_data jiffies_64; 82 extern unsigned long volatile __jiffy_data jiffies; 83 84 #if (BITS_PER_LONG < 64) 85 u64 get_jiffies_64(void); 86 #else 87 static inline u64 get_jiffies_64(void) 88 { 89 return (u64)jiffies; 90 } 91 #endif 92 93 /* 94 * These inlines deal with timer wrapping correctly. You are 95 * strongly encouraged to use them 96 * 1. Because people otherwise forget 97 * 2. Because if the timer wrap changes in future you won't have to 98 * alter your driver code. 99 * 100 * time_after(a,b) returns true if the time a is after time b. 101 * 102 * Do this with "<0" and ">=0" to only test the sign of the result. A 103 * good compiler would generate better code (and a really good compiler 104 * wouldn't care). Gcc is currently neither. 105 */ 106 #define time_after(a,b) \ 107 (typecheck(unsigned long, a) && \ 108 typecheck(unsigned long, b) && \ 109 ((long)(b) - (long)(a) < 0)) 110 #define time_before(a,b) time_after(b,a) 111 112 #define time_after_eq(a,b) \ 113 (typecheck(unsigned long, a) && \ 114 typecheck(unsigned long, b) && \ 115 ((long)(a) - (long)(b) >= 0)) 116 #define time_before_eq(a,b) time_after_eq(b,a) 117 118 /* Same as above, but does so with platform independent 64bit types. 119 * These must be used when utilizing jiffies_64 (i.e. return value of 120 * get_jiffies_64() */ 121 #define time_after64(a,b) \ 122 (typecheck(__u64, a) && \ 123 typecheck(__u64, b) && \ 124 ((__s64)(b) - (__s64)(a) < 0)) 125 #define time_before64(a,b) time_after64(b,a) 126 127 #define time_after_eq64(a,b) \ 128 (typecheck(__u64, a) && \ 129 typecheck(__u64, b) && \ 130 ((__s64)(a) - (__s64)(b) >= 0)) 131 #define time_before_eq64(a,b) time_after_eq64(b,a) 132 133 /* 134 * Have the 32 bit jiffies value wrap 5 minutes after boot 135 * so jiffies wrap bugs show up earlier. 136 */ 137 #define INITIAL_JIFFIES ((unsigned long)(unsigned int) (-300*HZ)) 138 139 /* 140 * Change timeval to jiffies, trying to avoid the 141 * most obvious overflows.. 142 * 143 * And some not so obvious. 144 * 145 * Note that we don't want to return LONG_MAX, because 146 * for various timeout reasons we often end up having 147 * to wait "jiffies+1" in order to guarantee that we wait 148 * at _least_ "jiffies" - so "jiffies+1" had better still 149 * be positive. 150 */ 151 #define MAX_JIFFY_OFFSET ((LONG_MAX >> 1)-1) 152 153 /* 154 * We want to do realistic conversions of time so we need to use the same 155 * values the update wall clock code uses as the jiffies size. This value 156 * is: TICK_NSEC (which is defined in timex.h). This 157 * is a constant and is in nanoseconds. We will used scaled math 158 * with a set of scales defined here as SEC_JIFFIE_SC, USEC_JIFFIE_SC and 159 * NSEC_JIFFIE_SC. Note that these defines contain nothing but 160 * constants and so are computed at compile time. SHIFT_HZ (computed in 161 * timex.h) adjusts the scaling for different HZ values. 162 163 * Scaled math??? What is that? 164 * 165 * Scaled math is a way to do integer math on values that would, 166 * otherwise, either overflow, underflow, or cause undesired div 167 * instructions to appear in the execution path. In short, we "scale" 168 * up the operands so they take more bits (more precision, less 169 * underflow), do the desired operation and then "scale" the result back 170 * by the same amount. If we do the scaling by shifting we avoid the 171 * costly mpy and the dastardly div instructions. 172 173 * Suppose, for example, we want to convert from seconds to jiffies 174 * where jiffies is defined in nanoseconds as NSEC_PER_JIFFIE. The 175 * simple math is: jiff = (sec * NSEC_PER_SEC) / NSEC_PER_JIFFIE; We 176 * observe that (NSEC_PER_SEC / NSEC_PER_JIFFIE) is a constant which we 177 * might calculate at compile time, however, the result will only have 178 * about 3-4 bits of precision (less for smaller values of HZ). 179 * 180 * So, we scale as follows: 181 * jiff = (sec) * (NSEC_PER_SEC / NSEC_PER_JIFFIE); 182 * jiff = ((sec) * ((NSEC_PER_SEC * SCALE)/ NSEC_PER_JIFFIE)) / SCALE; 183 * Then we make SCALE a power of two so: 184 * jiff = ((sec) * ((NSEC_PER_SEC << SCALE)/ NSEC_PER_JIFFIE)) >> SCALE; 185 * Now we define: 186 * #define SEC_CONV = ((NSEC_PER_SEC << SCALE)/ NSEC_PER_JIFFIE)) 187 * jiff = (sec * SEC_CONV) >> SCALE; 188 * 189 * Often the math we use will expand beyond 32-bits so we tell C how to 190 * do this and pass the 64-bit result of the mpy through the ">> SCALE" 191 * which should take the result back to 32-bits. We want this expansion 192 * to capture as much precision as possible. At the same time we don't 193 * want to overflow so we pick the SCALE to avoid this. In this file, 194 * that means using a different scale for each range of HZ values (as 195 * defined in timex.h). 196 * 197 * For those who want to know, gcc will give a 64-bit result from a "*" 198 * operator if the result is a long long AND at least one of the 199 * operands is cast to long long (usually just prior to the "*" so as 200 * not to confuse it into thinking it really has a 64-bit operand, 201 * which, buy the way, it can do, but it take more code and at least 2 202 * mpys). 203 204 * We also need to be aware that one second in nanoseconds is only a 205 * couple of bits away from overflowing a 32-bit word, so we MUST use 206 * 64-bits to get the full range time in nanoseconds. 207 208 */ 209 210 /* 211 * Here are the scales we will use. One for seconds, nanoseconds and 212 * microseconds. 213 * 214 * Within the limits of cpp we do a rough cut at the SEC_JIFFIE_SC and 215 * check if the sign bit is set. If not, we bump the shift count by 1. 216 * (Gets an extra bit of precision where we can use it.) 217 * We know it is set for HZ = 1024 and HZ = 100 not for 1000. 218 * Haven't tested others. 219 220 * Limits of cpp (for #if expressions) only long (no long long), but 221 * then we only need the most signicant bit. 222 */ 223 224 #define SEC_JIFFIE_SC (31 - SHIFT_HZ) 225 #if !((((NSEC_PER_SEC << 2) / TICK_NSEC) << (SEC_JIFFIE_SC - 2)) & 0x80000000) 226 #undef SEC_JIFFIE_SC 227 #define SEC_JIFFIE_SC (32 - SHIFT_HZ) 228 #endif 229 #define NSEC_JIFFIE_SC (SEC_JIFFIE_SC + 29) 230 #define USEC_JIFFIE_SC (SEC_JIFFIE_SC + 19) 231 #define SEC_CONVERSION ((unsigned long)((((u64)NSEC_PER_SEC << SEC_JIFFIE_SC) +\ 232 TICK_NSEC -1) / (u64)TICK_NSEC)) 233 234 #define NSEC_CONVERSION ((unsigned long)((((u64)1 << NSEC_JIFFIE_SC) +\ 235 TICK_NSEC -1) / (u64)TICK_NSEC)) 236 #define USEC_CONVERSION \ 237 ((unsigned long)((((u64)NSEC_PER_USEC << USEC_JIFFIE_SC) +\ 238 TICK_NSEC -1) / (u64)TICK_NSEC)) 239 /* 240 * USEC_ROUND is used in the timeval to jiffie conversion. See there 241 * for more details. It is the scaled resolution rounding value. Note 242 * that it is a 64-bit value. Since, when it is applied, we are already 243 * in jiffies (albit scaled), it is nothing but the bits we will shift 244 * off. 245 */ 246 #define USEC_ROUND (u64)(((u64)1 << USEC_JIFFIE_SC) - 1) 247 /* 248 * The maximum jiffie value is (MAX_INT >> 1). Here we translate that 249 * into seconds. The 64-bit case will overflow if we are not careful, 250 * so use the messy SH_DIV macro to do it. Still all constants. 251 */ 252 #if BITS_PER_LONG < 64 253 # define MAX_SEC_IN_JIFFIES \ 254 (long)((u64)((u64)MAX_JIFFY_OFFSET * TICK_NSEC) / NSEC_PER_SEC) 255 #else /* take care of overflow on 64 bits machines */ 256 # define MAX_SEC_IN_JIFFIES \ 257 (SH_DIV((MAX_JIFFY_OFFSET >> SEC_JIFFIE_SC) * TICK_NSEC, NSEC_PER_SEC, 1) - 1) 258 259 #endif 260 261 /* 262 * Convert various time units to each other: 263 */ 264 extern unsigned int jiffies_to_msecs(const unsigned long j); 265 extern unsigned int jiffies_to_usecs(const unsigned long j); 266 extern unsigned long msecs_to_jiffies(const unsigned int m); 267 extern unsigned long usecs_to_jiffies(const unsigned int u); 268 extern unsigned long timespec_to_jiffies(const struct timespec *value); 269 extern void jiffies_to_timespec(const unsigned long jiffies, 270 struct timespec *value); 271 extern unsigned long timeval_to_jiffies(const struct timeval *value); 272 extern void jiffies_to_timeval(const unsigned long jiffies, 273 struct timeval *value); 274 extern clock_t jiffies_to_clock_t(long x); 275 extern unsigned long clock_t_to_jiffies(unsigned long x); 276 extern u64 jiffies_64_to_clock_t(u64 x); 277 extern u64 nsec_to_clock_t(u64 x); 278 279 #define TIMESTAMP_SIZE 30 280 281 #endif 282