| 1 | /* |
| 2 | * sched_clock for unstable cpu clocks |
| 3 | * |
| 4 | * Copyright (C) 2008 Red Hat, Inc., Peter Zijlstra <pzijlstr@redhat.com> |
| 5 | * |
| 6 | * Updates and enhancements: |
| 7 | * Copyright (C) 2008 Red Hat, Inc. Steven Rostedt <srostedt@redhat.com> |
| 8 | * |
| 9 | * Based on code by: |
| 10 | * Ingo Molnar <mingo@redhat.com> |
| 11 | * Guillaume Chazarain <guichaz@gmail.com> |
| 12 | * |
| 13 | * |
| 14 | * What: |
| 15 | * |
| 16 | * cpu_clock(i) provides a fast (execution time) high resolution |
| 17 | * clock with bounded drift between CPUs. The value of cpu_clock(i) |
| 18 | * is monotonic for constant i. The timestamp returned is in nanoseconds. |
| 19 | * |
| 20 | * ######################### BIG FAT WARNING ########################## |
| 21 | * # when comparing cpu_clock(i) to cpu_clock(j) for i != j, time can # |
| 22 | * # go backwards !! # |
| 23 | * #################################################################### |
| 24 | * |
| 25 | * There is no strict promise about the base, although it tends to start |
| 26 | * at 0 on boot (but people really shouldn't rely on that). |
| 27 | * |
| 28 | * cpu_clock(i) -- can be used from any context, including NMI. |
| 29 | * sched_clock_cpu(i) -- must be used with local IRQs disabled (implied by NMI) |
| 30 | * local_clock() -- is cpu_clock() on the current cpu. |
| 31 | * |
| 32 | * How: |
| 33 | * |
| 34 | * The implementation either uses sched_clock() when |
| 35 | * !CONFIG_HAVE_UNSTABLE_SCHED_CLOCK, which means in that case the |
| 36 | * sched_clock() is assumed to provide these properties (mostly it means |
| 37 | * the architecture provides a globally synchronized highres time source). |
| 38 | * |
| 39 | * Otherwise it tries to create a semi stable clock from a mixture of other |
| 40 | * clocks, including: |
| 41 | * |
| 42 | * - GTOD (clock monotomic) |
| 43 | * - sched_clock() |
| 44 | * - explicit idle events |
| 45 | * |
| 46 | * We use GTOD as base and use sched_clock() deltas to improve resolution. The |
| 47 | * deltas are filtered to provide monotonicity and keeping it within an |
| 48 | * expected window. |
| 49 | * |
| 50 | * Furthermore, explicit sleep and wakeup hooks allow us to account for time |
| 51 | * that is otherwise invisible (TSC gets stopped). |
| 52 | * |
| 53 | * |
| 54 | * Notes: |
| 55 | * |
| 56 | * The !IRQ-safetly of sched_clock() and sched_clock_cpu() comes from things |
| 57 | * like cpufreq interrupts that can change the base clock (TSC) multiplier |
| 58 | * and cause funny jumps in time -- although the filtering provided by |
| 59 | * sched_clock_cpu() should mitigate serious artifacts we cannot rely on it |
| 60 | * in general since for !CONFIG_HAVE_UNSTABLE_SCHED_CLOCK we fully rely on |
| 61 | * sched_clock(). |
| 62 | */ |
| 63 | #include <linux/spinlock.h> |
| 64 | #include <linux/hardirq.h> |
| 65 | #include <linux/export.h> |
| 66 | #include <linux/percpu.h> |
| 67 | #include <linux/ktime.h> |
| 68 | #include <linux/sched.h> |
| 69 | |
| 70 | /* |
| 71 | * Scheduler clock - returns current time in nanosec units. |
| 72 | * This is default implementation. |
| 73 | * Architectures and sub-architectures can override this. |
| 74 | */ |
| 75 | unsigned long long __attribute__((weak)) sched_clock(void) |
| 76 | { |
| 77 | return (unsigned long long)(jiffies - INITIAL_JIFFIES) |
| 78 | * (NSEC_PER_SEC / HZ); |
| 79 | } |
| 80 | EXPORT_SYMBOL_GPL(sched_clock); |
| 81 | |
| 82 | __read_mostly int sched_clock_running; |
| 83 | |
| 84 | #ifdef CONFIG_HAVE_UNSTABLE_SCHED_CLOCK |
| 85 | __read_mostly int sched_clock_stable; |
| 86 | |
| 87 | struct sched_clock_data { |
| 88 | u64 tick_raw; |
| 89 | u64 tick_gtod; |
| 90 | u64 clock; |
| 91 | }; |
| 92 | |
| 93 | static DEFINE_PER_CPU_SHARED_ALIGNED(struct sched_clock_data, sched_clock_data); |
| 94 | |
| 95 | static inline struct sched_clock_data *this_scd(void) |
| 96 | { |
| 97 | return &__get_cpu_var(sched_clock_data); |
| 98 | } |
| 99 | |
| 100 | static inline struct sched_clock_data *cpu_sdc(int cpu) |
| 101 | { |
| 102 | return &per_cpu(sched_clock_data, cpu); |
| 103 | } |
| 104 | |
| 105 | void sched_clock_init(void) |
| 106 | { |
| 107 | u64 ktime_now = ktime_to_ns(ktime_get()); |
| 108 | int cpu; |
| 109 | |
| 110 | for_each_possible_cpu(cpu) { |
| 111 | struct sched_clock_data *scd = cpu_sdc(cpu); |
| 112 | |
| 113 | scd->tick_raw = 0; |
| 114 | scd->tick_gtod = ktime_now; |
| 115 | scd->clock = ktime_now; |
| 116 | } |
| 117 | |
| 118 | sched_clock_running = 1; |
| 119 | } |
| 120 | |
| 121 | /* |
| 122 | * min, max except they take wrapping into account |
| 123 | */ |
| 124 | |
| 125 | static inline u64 wrap_min(u64 x, u64 y) |
| 126 | { |
| 127 | return (s64)(x - y) < 0 ? x : y; |
| 128 | } |
| 129 | |
| 130 | static inline u64 wrap_max(u64 x, u64 y) |
| 131 | { |
| 132 | return (s64)(x - y) > 0 ? x : y; |
| 133 | } |
| 134 | |
| 135 | /* |
| 136 | * update the percpu scd from the raw @now value |
| 137 | * |
| 138 | * - filter out backward motion |
| 139 | * - use the GTOD tick value to create a window to filter crazy TSC values |
| 140 | */ |
| 141 | static u64 sched_clock_local(struct sched_clock_data *scd) |
| 142 | { |
| 143 | u64 now, clock, old_clock, min_clock, max_clock; |
| 144 | s64 delta; |
| 145 | |
| 146 | again: |
| 147 | now = sched_clock(); |
| 148 | delta = now - scd->tick_raw; |
| 149 | if (unlikely(delta < 0)) |
| 150 | delta = 0; |
| 151 | |
| 152 | old_clock = scd->clock; |
| 153 | |
| 154 | /* |
| 155 | * scd->clock = clamp(scd->tick_gtod + delta, |
| 156 | * max(scd->tick_gtod, scd->clock), |
| 157 | * scd->tick_gtod + TICK_NSEC); |
| 158 | */ |
| 159 | |
| 160 | clock = scd->tick_gtod + delta; |
| 161 | min_clock = wrap_max(scd->tick_gtod, old_clock); |
| 162 | max_clock = wrap_max(old_clock, scd->tick_gtod + TICK_NSEC); |
| 163 | |
| 164 | clock = wrap_max(clock, min_clock); |
| 165 | clock = wrap_min(clock, max_clock); |
| 166 | |
| 167 | if (cmpxchg64(&scd->clock, old_clock, clock) != old_clock) |
| 168 | goto again; |
| 169 | |
| 170 | return clock; |
| 171 | } |
| 172 | |
| 173 | static u64 sched_clock_remote(struct sched_clock_data *scd) |
| 174 | { |
| 175 | struct sched_clock_data *my_scd = this_scd(); |
| 176 | u64 this_clock, remote_clock; |
| 177 | u64 *ptr, old_val, val; |
| 178 | |
| 179 | #if BITS_PER_LONG != 64 |
| 180 | again: |
| 181 | /* |
| 182 | * Careful here: The local and the remote clock values need to |
| 183 | * be read out atomic as we need to compare the values and |
| 184 | * then update either the local or the remote side. So the |
| 185 | * cmpxchg64 below only protects one readout. |
| 186 | * |
| 187 | * We must reread via sched_clock_local() in the retry case on |
| 188 | * 32bit as an NMI could use sched_clock_local() via the |
| 189 | * tracer and hit between the readout of |
| 190 | * the low32bit and the high 32bit portion. |
| 191 | */ |
| 192 | this_clock = sched_clock_local(my_scd); |
| 193 | /* |
| 194 | * We must enforce atomic readout on 32bit, otherwise the |
| 195 | * update on the remote cpu can hit inbetween the readout of |
| 196 | * the low32bit and the high 32bit portion. |
| 197 | */ |
| 198 | remote_clock = cmpxchg64(&scd->clock, 0, 0); |
| 199 | #else |
| 200 | /* |
| 201 | * On 64bit the read of [my]scd->clock is atomic versus the |
| 202 | * update, so we can avoid the above 32bit dance. |
| 203 | */ |
| 204 | sched_clock_local(my_scd); |
| 205 | again: |
| 206 | this_clock = my_scd->clock; |
| 207 | remote_clock = scd->clock; |
| 208 | #endif |
| 209 | |
| 210 | /* |
| 211 | * Use the opportunity that we have both locks |
| 212 | * taken to couple the two clocks: we take the |
| 213 | * larger time as the latest time for both |
| 214 | * runqueues. (this creates monotonic movement) |
| 215 | */ |
| 216 | if (likely((s64)(remote_clock - this_clock) < 0)) { |
| 217 | ptr = &scd->clock; |
| 218 | old_val = remote_clock; |
| 219 | val = this_clock; |
| 220 | } else { |
| 221 | /* |
| 222 | * Should be rare, but possible: |
| 223 | */ |
| 224 | ptr = &my_scd->clock; |
| 225 | old_val = this_clock; |
| 226 | val = remote_clock; |
| 227 | } |
| 228 | |
| 229 | if (cmpxchg64(ptr, old_val, val) != old_val) |
| 230 | goto again; |
| 231 | |
| 232 | return val; |
| 233 | } |
| 234 | |
| 235 | /* |
| 236 | * Similar to cpu_clock(), but requires local IRQs to be disabled. |
| 237 | * |
| 238 | * See cpu_clock(). |
| 239 | */ |
| 240 | u64 sched_clock_cpu(int cpu) |
| 241 | { |
| 242 | struct sched_clock_data *scd; |
| 243 | u64 clock; |
| 244 | |
| 245 | WARN_ON_ONCE(!irqs_disabled()); |
| 246 | |
| 247 | if (sched_clock_stable) |
| 248 | return sched_clock(); |
| 249 | |
| 250 | if (unlikely(!sched_clock_running)) |
| 251 | return 0ull; |
| 252 | |
| 253 | scd = cpu_sdc(cpu); |
| 254 | |
| 255 | if (cpu != smp_processor_id()) |
| 256 | clock = sched_clock_remote(scd); |
| 257 | else |
| 258 | clock = sched_clock_local(scd); |
| 259 | |
| 260 | return clock; |
| 261 | } |
| 262 | |
| 263 | void sched_clock_tick(void) |
| 264 | { |
| 265 | struct sched_clock_data *scd; |
| 266 | u64 now, now_gtod; |
| 267 | |
| 268 | if (sched_clock_stable) |
| 269 | return; |
| 270 | |
| 271 | if (unlikely(!sched_clock_running)) |
| 272 | return; |
| 273 | |
| 274 | WARN_ON_ONCE(!irqs_disabled()); |
| 275 | |
| 276 | scd = this_scd(); |
| 277 | now_gtod = ktime_to_ns(ktime_get()); |
| 278 | now = sched_clock(); |
| 279 | |
| 280 | scd->tick_raw = now; |
| 281 | scd->tick_gtod = now_gtod; |
| 282 | sched_clock_local(scd); |
| 283 | } |
| 284 | |
| 285 | /* |
| 286 | * We are going deep-idle (irqs are disabled): |
| 287 | */ |
| 288 | void sched_clock_idle_sleep_event(void) |
| 289 | { |
| 290 | sched_clock_cpu(smp_processor_id()); |
| 291 | } |
| 292 | EXPORT_SYMBOL_GPL(sched_clock_idle_sleep_event); |
| 293 | |
| 294 | /* |
| 295 | * We just idled delta nanoseconds (called with irqs disabled): |
| 296 | */ |
| 297 | void sched_clock_idle_wakeup_event(u64 delta_ns) |
| 298 | { |
| 299 | if (timekeeping_suspended) |
| 300 | return; |
| 301 | |
| 302 | sched_clock_tick(); |
| 303 | touch_softlockup_watchdog(); |
| 304 | } |
| 305 | EXPORT_SYMBOL_GPL(sched_clock_idle_wakeup_event); |
| 306 | |
| 307 | /* |
| 308 | * As outlined at the top, provides a fast, high resolution, nanosecond |
| 309 | * time source that is monotonic per cpu argument and has bounded drift |
| 310 | * between cpus. |
| 311 | * |
| 312 | * ######################### BIG FAT WARNING ########################## |
| 313 | * # when comparing cpu_clock(i) to cpu_clock(j) for i != j, time can # |
| 314 | * # go backwards !! # |
| 315 | * #################################################################### |
| 316 | */ |
| 317 | u64 cpu_clock(int cpu) |
| 318 | { |
| 319 | u64 clock; |
| 320 | unsigned long flags; |
| 321 | |
| 322 | local_irq_save(flags); |
| 323 | clock = sched_clock_cpu(cpu); |
| 324 | local_irq_restore(flags); |
| 325 | |
| 326 | return clock; |
| 327 | } |
| 328 | |
| 329 | /* |
| 330 | * Similar to cpu_clock() for the current cpu. Time will only be observed |
| 331 | * to be monotonic if care is taken to only compare timestampt taken on the |
| 332 | * same CPU. |
| 333 | * |
| 334 | * See cpu_clock(). |
| 335 | */ |
| 336 | u64 local_clock(void) |
| 337 | { |
| 338 | u64 clock; |
| 339 | unsigned long flags; |
| 340 | |
| 341 | local_irq_save(flags); |
| 342 | clock = sched_clock_cpu(smp_processor_id()); |
| 343 | local_irq_restore(flags); |
| 344 | |
| 345 | return clock; |
| 346 | } |
| 347 | |
| 348 | #else /* CONFIG_HAVE_UNSTABLE_SCHED_CLOCK */ |
| 349 | |
| 350 | void sched_clock_init(void) |
| 351 | { |
| 352 | sched_clock_running = 1; |
| 353 | } |
| 354 | |
| 355 | u64 sched_clock_cpu(int cpu) |
| 356 | { |
| 357 | if (unlikely(!sched_clock_running)) |
| 358 | return 0; |
| 359 | |
| 360 | return sched_clock(); |
| 361 | } |
| 362 | |
| 363 | u64 cpu_clock(int cpu) |
| 364 | { |
| 365 | return sched_clock_cpu(cpu); |
| 366 | } |
| 367 | |
| 368 | u64 local_clock(void) |
| 369 | { |
| 370 | return sched_clock_cpu(0); |
| 371 | } |
| 372 | |
| 373 | #endif /* CONFIG_HAVE_UNSTABLE_SCHED_CLOCK */ |
| 374 | |
| 375 | EXPORT_SYMBOL_GPL(cpu_clock); |
| 376 | EXPORT_SYMBOL_GPL(local_clock); |