wrapper/trace-clock.h

   1 /* SPDX-License-Identifier: (GPL-2.0-only or LGPL-2.1-only)
   2  *
   3  * wrapper/trace-clock.h
   4  *
   5  * Contains LTTng trace clock mapping to LTTng trace clock or mainline monotonic
   6  * clock. This wrapper depends on CONFIG_HIGH_RES_TIMERS=y.
   7  *
   8  * Copyright (C) 2011-2012 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
   9  */
  10
  11 #ifndef _LTTNG_TRACE_CLOCK_H
  12 #define _LTTNG_TRACE_CLOCK_H
  13
  14 #ifdef CONFIG_HAVE_TRACE_CLOCK
  15 #include <linux/trace-clock.h>
  16 #else /* CONFIG_HAVE_TRACE_CLOCK */
  17
  18 #include <linux/hardirq.h>
  19 #include <linux/ktime.h>
  20 #include <linux/time.h>
  21 #include <linux/hrtimer.h>
  22 #include <linux/percpu.h>
  23 #include <linux/version.h>
  24 #include <asm/local.h>
  25 #include <lttng-kernel-version.h>
  26 #include <lttng-clock.h>
  27 #include <wrapper/compiler.h>
  28 #include <wrapper/percpu-defs.h>
  29 #include <wrapper/random.h>
  30 #include <blacklist/timekeeping.h>
  31
  32 extern struct lttng_trace_clock *lttng_trace_clock;
  33
  34 /*
  35  * Upstream Linux commit 27727df240c7 ("Avoid taking lock in NMI path with
  36  * CONFIG_DEBUG_TIMEKEEPING") introduces a buggy ktime_get_mono_fast_ns().
  37  * This is fixed by patch "timekeeping: Fix __ktime_get_fast_ns() regression".
  38  */
  39 #if (LTTNG_KERNEL_RANGE(4,8,0, 4,8,2) \
  40         || LTTNG_KERNEL_RANGE(4,7,4, 4,7,8) \
  41         || LTTNG_KERNEL_RANGE(4,4,20, 4,4,25) \
  42         || LTTNG_KERNEL_RANGE(4,1,32, 4,1,35))
  43 #define LTTNG_CLOCK_NMI_SAFE_BROKEN
  44 #endif
  45
  46 /*
  47  * We need clock values to be monotonically increasing per-cpu, which is
  48  * not strictly guaranteed by ktime_get_mono_fast_ns(). It is
  49  * straightforward to do on architectures with a 64-bit cmpxchg(), but
  50  * not so on architectures without 64-bit cmpxchg. For now, only enable
  51  * this feature on 64-bit architectures.
  52  */
  53
  54 #if (LINUX_VERSION_CODE >= KERNEL_VERSION(3,17,0) \
  55         && BITS_PER_LONG == 64 \
  56         && !defined(LTTNG_CLOCK_NMI_SAFE_BROKEN))
  57 #define LTTNG_USE_NMI_SAFE_CLOCK
  58 #endif
  59
  60 #ifdef LTTNG_USE_NMI_SAFE_CLOCK
  61
  62 DECLARE_PER_CPU(u64, lttng_last_tsc);
  63
  64 /*
  65  * Sometimes called with preemption enabled. Can be interrupted.
  66  */
  67 static inline u64 trace_clock_monotonic_wrapper(void)
  68 {
  69         u64 now, last, result;
  70         u64 *last_tsc_ptr;
  71
  72         /* Use fast nmi-safe monotonic clock provided by the Linux kernel. */
  73         preempt_disable();
  74         last_tsc_ptr = lttng_this_cpu_ptr(&lttng_last_tsc);
  75         last = *last_tsc_ptr;
  76         /*
  77          * Read "last" before "now". It is not strictly required, but it ensures
  78          * that an interrupt coming in won't artificially trigger a case where
  79          * "now" < "last". This kind of situation should only happen if the
  80          * mono_fast time source goes slightly backwards.
  81          */
  82         barrier();
  83         now = ktime_get_mono_fast_ns();
  84         if (U64_MAX / 2 < now - last)
  85                 now = last;
  86         result = cmpxchg64_local(last_tsc_ptr, last, now);
  87         preempt_enable();
  88         if (result == last) {
  89                 /* Update done. */
  90                 return now;
  91         } else {
  92                 /*
  93                  * Update not done, due to concurrent update. We can use
  94                  * "result", since it has been sampled concurrently with our
  95                  * time read, so it should not be far from "now".
  96                  */
  97                 return result;
  98         }
  99 }
 100
 101 #else /* #ifdef LTTNG_USE_NMI_SAFE_CLOCK */
 102 static inline u64 trace_clock_monotonic_wrapper(void)
 103 {
 104         ktime_t ktime;
 105
 106         /*
 107          * Refuse to trace from NMIs with this wrapper, because an NMI could
 108          * nest over the xtime write seqlock and deadlock.
 109          */
 110         if (in_nmi())
 111                 return (u64) -EIO;
 112
 113         ktime = ktime_get();
 114         return ktime_to_ns(ktime);
 115 }
 116 #endif /* #else #ifdef LTTNG_USE_NMI_SAFE_CLOCK */
 117
 118 static inline u64 trace_clock_read64_monotonic(void)
 119 {
 120         return (u64) trace_clock_monotonic_wrapper();
 121 }
 122
 123 static inline u64 trace_clock_freq_monotonic(void)
 124 {
 125         return (u64) NSEC_PER_SEC;
 126 }
 127
 128 static inline int trace_clock_uuid_monotonic(char *uuid)
 129 {
 130         return wrapper_get_bootid(uuid);
 131 }
 132
 133 static inline const char *trace_clock_name_monotonic(void)
 134 {
 135         return "monotonic";
 136 }
 137
 138 static inline const char *trace_clock_description_monotonic(void)
 139 {
 140         return "Monotonic Clock";
 141 }
 142
 143 #ifdef LTTNG_USE_NMI_SAFE_CLOCK
 144 static inline int get_trace_clock(void)
 145 {
 146         printk_once(KERN_WARNING "LTTng: Using mainline kernel monotonic fast clock, which is NMI-safe.\n");
 147         return 0;
 148 }
 149 #else /* #ifdef LTTNG_USE_NMI_SAFE_CLOCK */
 150 static inline int get_trace_clock(void)
 151 {
 152         printk_once(KERN_WARNING "LTTng: Using mainline kernel monotonic clock. NMIs will not be traced.\n");
 153         return 0;
 154 }
 155 #endif /* #else #ifdef LTTNG_USE_NMI_SAFE_CLOCK */
 156
 157 static inline void put_trace_clock(void)
 158 {
 159 }
 160
 161 static inline u64 trace_clock_read64(void)
 162 {
 163         struct lttng_trace_clock *ltc = READ_ONCE(lttng_trace_clock);
 164
 165         if (likely(!ltc)) {
 166                 return trace_clock_read64_monotonic();
 167         } else {
 168                 read_barrier_depends(); /* load ltc before content */
 169                 return ltc->read64();
 170         }
 171 }
 172
 173 static inline u64 trace_clock_freq(void)
 174 {
 175         struct lttng_trace_clock *ltc = READ_ONCE(lttng_trace_clock);
 176
 177         if (!ltc) {
 178                 return trace_clock_freq_monotonic();
 179         } else {
 180                 read_barrier_depends(); /* load ltc before content */
 181                 return ltc->freq();
 182         }
 183 }
 184
 185 static inline int trace_clock_uuid(char *uuid)
 186 {
 187         struct lttng_trace_clock *ltc = READ_ONCE(lttng_trace_clock);
 188
 189         read_barrier_depends(); /* load ltc before content */
 190         /* Use default UUID cb when NULL */
 191         if (!ltc || !ltc->uuid) {
 192                 return trace_clock_uuid_monotonic(uuid);
 193         } else {
 194                 return ltc->uuid(uuid);
 195         }
 196 }
 197
 198 static inline const char *trace_clock_name(void)
 199 {
 200         struct lttng_trace_clock *ltc = READ_ONCE(lttng_trace_clock);
 201
 202         if (!ltc) {
 203                 return trace_clock_name_monotonic();
 204         } else {
 205                 read_barrier_depends(); /* load ltc before content */
 206                 return ltc->name();
 207         }
 208 }
 209
 210 static inline const char *trace_clock_description(void)
 211 {
 212         struct lttng_trace_clock *ltc = READ_ONCE(lttng_trace_clock);
 213
 214         if (!ltc) {
 215                 return trace_clock_description_monotonic();
 216         } else {
 217                 read_barrier_depends(); /* load ltc before content */
 218                 return ltc->description();
 219         }
 220 }
 221
 222 #endif /* CONFIG_HAVE_TRACE_CLOCK */
 223
 224 #endif /* _LTTNG_TRACE_CLOCK_H */