wrapper/trace-clock.h

   1 /* SPDX-License-Identifier: (GPL-2.0 or LGPL-2.1)
   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
  31 #if ((LTTNG_KERNEL_RANGE(3,10,0, 3,10,14) && !LTTNG_RHEL_KERNEL_RANGE(3,10,0,123,0,0, 3,10,14,0,0,0)) \
  32         || LTTNG_KERNEL_RANGE(3,11,0, 3,11,3))
  33 #error "Linux kernels 3.10 and 3.11 introduce a deadlock in the timekeeping subsystem. Fixed by commit 7bd36014460f793c19e7d6c94dab67b0afcfcb7f \"timekeeping: Fix HRTICK related deadlock from ntp lock changes\" in Linux."
  34 #endif
  35
  36 extern struct lttng_trace_clock *lttng_trace_clock;
  37
  38 /*
  39  * Upstream Linux commit 27727df240c7 ("Avoid taking lock in NMI path with
  40  * CONFIG_DEBUG_TIMEKEEPING") introduces a buggy ktime_get_mono_fast_ns().
  41  * This is fixed by patch "timekeeping: Fix __ktime_get_fast_ns() regression".
  42  */
  43 #if (LTTNG_KERNEL_RANGE(4,8,0, 4,8,2) \
  44         || LTTNG_KERNEL_RANGE(4,7,4, 4,7,8) \
  45         || LTTNG_KERNEL_RANGE(4,4,20, 4,4,25) \
  46         || LTTNG_KERNEL_RANGE(4,1,32, 4,1,35))
  47 #define LTTNG_CLOCK_NMI_SAFE_BROKEN
  48 #endif
  49
  50 /*
  51  * We need clock values to be monotonically increasing per-cpu, which is
  52  * not strictly guaranteed by ktime_get_mono_fast_ns(). It is
  53  * straightforward to do on architectures with a 64-bit cmpxchg(), but
  54  * not so on architectures without 64-bit cmpxchg. For now, only enable
  55  * this feature on 64-bit architectures.
  56  */
  57
  58 #if (LINUX_VERSION_CODE >= KERNEL_VERSION(3,17,0) \
  59         && BITS_PER_LONG == 64 \
  60         && !defined(LTTNG_CLOCK_NMI_SAFE_BROKEN))
  61 #define LTTNG_USE_NMI_SAFE_CLOCK
  62 #endif
  63
  64 #ifdef LTTNG_USE_NMI_SAFE_CLOCK
  65
  66 DECLARE_PER_CPU(u64, lttng_last_tsc);
  67
  68 /*
  69  * Sometimes called with preemption enabled. Can be interrupted.
  70  */
  71 static inline u64 trace_clock_monotonic_wrapper(void)
  72 {
  73         u64 now, last, result;
  74         u64 *last_tsc_ptr;
  75
  76         /* Use fast nmi-safe monotonic clock provided by the Linux kernel. */
  77         preempt_disable();
  78         last_tsc_ptr = lttng_this_cpu_ptr(&lttng_last_tsc);
  79         last = *last_tsc_ptr;
  80         /*
  81          * Read "last" before "now". It is not strictly required, but it ensures
  82          * that an interrupt coming in won't artificially trigger a case where
  83          * "now" < "last". This kind of situation should only happen if the
  84          * mono_fast time source goes slightly backwards.
  85          */
  86         barrier();
  87         now = ktime_get_mono_fast_ns();
  88         if (U64_MAX / 2 < now - last)
  89                 now = last;
  90         result = cmpxchg64_local(last_tsc_ptr, last, now);
  91         preempt_enable();
  92         if (result == last) {
  93                 /* Update done. */
  94                 return now;
  95         } else {
  96                 /*
  97                  * Update not done, due to concurrent update. We can use
  98                  * "result", since it has been sampled concurrently with our
  99                  * time read, so it should not be far from "now".
 100                  */
 101                 return result;
 102         }
 103 }
 104
 105 #else /* #ifdef LTTNG_USE_NMI_SAFE_CLOCK */
 106 static inline u64 trace_clock_monotonic_wrapper(void)
 107 {
 108         ktime_t ktime;
 109
 110         /*
 111          * Refuse to trace from NMIs with this wrapper, because an NMI could
 112          * nest over the xtime write seqlock and deadlock.
 113          */
 114         if (in_nmi())
 115                 return (u64) -EIO;
 116
 117         ktime = ktime_get();
 118         return ktime_to_ns(ktime);
 119 }
 120 #endif /* #else #ifdef LTTNG_USE_NMI_SAFE_CLOCK */
 121
 122 static inline u64 trace_clock_read64_monotonic(void)
 123 {
 124         return (u64) trace_clock_monotonic_wrapper();
 125 }
 126
 127 static inline u64 trace_clock_freq_monotonic(void)
 128 {
 129         return (u64) NSEC_PER_SEC;
 130 }
 131
 132 static inline int trace_clock_uuid_monotonic(char *uuid)
 133 {
 134         return wrapper_get_bootid(uuid);
 135 }
 136
 137 static inline const char *trace_clock_name_monotonic(void)
 138 {
 139         return "monotonic";
 140 }
 141
 142 static inline const char *trace_clock_description_monotonic(void)
 143 {
 144         return "Monotonic Clock";
 145 }
 146
 147 #ifdef LTTNG_USE_NMI_SAFE_CLOCK
 148 static inline int get_trace_clock(void)
 149 {
 150         printk_once(KERN_WARNING "LTTng: Using mainline kernel monotonic fast clock, which is NMI-safe.\n");
 151         return 0;
 152 }
 153 #else /* #ifdef LTTNG_USE_NMI_SAFE_CLOCK */
 154 static inline int get_trace_clock(void)
 155 {
 156         printk_once(KERN_WARNING "LTTng: Using mainline kernel monotonic clock. NMIs will not be traced.\n");
 157         return 0;
 158 }
 159 #endif /* #else #ifdef LTTNG_USE_NMI_SAFE_CLOCK */
 160
 161 static inline void put_trace_clock(void)
 162 {
 163 }
 164
 165 static inline u64 trace_clock_read64(void)
 166 {
 167         struct lttng_trace_clock *ltc = READ_ONCE(lttng_trace_clock);
 168
 169         if (likely(!ltc)) {
 170                 return trace_clock_read64_monotonic();
 171         } else {
 172                 read_barrier_depends(); /* load ltc before content */
 173                 return ltc->read64();
 174         }
 175 }
 176
 177 static inline u64 trace_clock_freq(void)
 178 {
 179         struct lttng_trace_clock *ltc = READ_ONCE(lttng_trace_clock);
 180
 181         if (!ltc) {
 182                 return trace_clock_freq_monotonic();
 183         } else {
 184                 read_barrier_depends(); /* load ltc before content */
 185                 return ltc->freq();
 186         }
 187 }
 188
 189 static inline int trace_clock_uuid(char *uuid)
 190 {
 191         struct lttng_trace_clock *ltc = READ_ONCE(lttng_trace_clock);
 192
 193         read_barrier_depends(); /* load ltc before content */
 194         /* Use default UUID cb when NULL */
 195         if (!ltc || !ltc->uuid) {
 196                 return trace_clock_uuid_monotonic(uuid);
 197         } else {
 198                 return ltc->uuid(uuid);
 199         }
 200 }
 201
 202 static inline const char *trace_clock_name(void)
 203 {
 204         struct lttng_trace_clock *ltc = READ_ONCE(lttng_trace_clock);
 205
 206         if (!ltc) {
 207                 return trace_clock_name_monotonic();
 208         } else {
 209                 read_barrier_depends(); /* load ltc before content */
 210                 return ltc->name();
 211         }
 212 }
 213
 214 static inline const char *trace_clock_description(void)
 215 {
 216         struct lttng_trace_clock *ltc = READ_ONCE(lttng_trace_clock);
 217
 218         if (!ltc) {
 219                 return trace_clock_description_monotonic();
 220         } else {
 221                 read_barrier_depends(); /* load ltc before content */
 222                 return ltc->description();
 223         }
 224 }
 225
 226 #endif /* CONFIG_HAVE_TRACE_CLOCK */
 227
 228 #endif /* _LTTNG_TRACE_CLOCK_H */