| 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 | #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(<tng_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 */ |