wrapper/trace-clock.h

   1 #ifndef _LTTNG_TRACE_CLOCK_H
   2 #define _LTTNG_TRACE_CLOCK_H
   3
   4 /*
   5  * wrapper/trace-clock.h
   6  *
   7  * Contains LTTng trace clock mapping to LTTng trace clock or mainline monotonic
   8  * clock. This wrapper depends on CONFIG_HIGH_RES_TIMERS=y.
   9  *
  10  * Copyright (C) 2011-2012 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
  11  *
  12  * This library is free software; you can redistribute it and/or
  13  * modify it under the terms of the GNU Lesser General Public
  14  * License as published by the Free Software Foundation; only
  15  * version 2.1 of the License.
  16  *
  17  * This library is distributed in the hope that it will be useful,
  18  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  19  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
  20  * Lesser General Public License for more details.
  21  *
  22  * You should have received a copy of the GNU Lesser General Public
  23  * License along with this library; if not, write to the Free Software
  24  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  25  */
  26
  27 #ifdef CONFIG_HAVE_TRACE_CLOCK
  28 #include <linux/trace-clock.h>
  29 #else /* CONFIG_HAVE_TRACE_CLOCK */
  30
  31 #include <linux/hardirq.h>
  32 #include <linux/ktime.h>
  33 #include <linux/time.h>
  34 #include <linux/hrtimer.h>
  35 #include <linux/percpu.h>
  36 #include <linux/version.h>
  37 #include <asm/local.h>
  38 #include <lttng-kernel-version.h>
  39 #include <lttng-clock.h>
  40 #include <wrapper/compiler.h>
  41 #include <wrapper/percpu-defs.h>
  42 #include <wrapper/random.h>
  43
  44 #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)) \
  45         || LTTNG_KERNEL_RANGE(3,11,0, 3,11,3))
  46 #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."
  47 #endif
  48
  49 extern struct lttng_trace_clock *lttng_trace_clock;
  50
  51 /*
  52  * Upstream Linux commit 27727df240c7 ("Avoid taking lock in NMI path with
  53  * CONFIG_DEBUG_TIMEKEEPING") introduces a buggy ktime_get_mono_fast_ns().
  54  * This is fixed by patch "timekeeping: Fix __ktime_get_fast_ns() regression".
  55  */
  56 #if (LTTNG_KERNEL_RANGE(4,8,0, 4,8,2) \
  57         || LTTNG_KERNEL_RANGE(4,7,4, 4,7,8) \
  58         || LTTNG_KERNEL_RANGE(4,4,20, 4,4,25) \
  59         || LTTNG_KERNEL_RANGE(4,1,32, 4,1,35))
  60 #define LTTNG_CLOCK_NMI_SAFE_BROKEN
  61 #endif
  62
  63 /*
  64  * We need clock values to be monotonically increasing per-cpu, which is
  65  * not strictly guaranteed by ktime_get_mono_fast_ns(). It is
  66  * straightforward to do on architectures with a 64-bit cmpxchg(), but
  67  * not so on architectures without 64-bit cmpxchg. For now, only enable
  68  * this feature on 64-bit architectures.
  69  */
  70
  71 #if (LINUX_VERSION_CODE >= KERNEL_VERSION(3,17,0) \
  72         && BITS_PER_LONG == 64 \
  73         && !defined(LTTNG_CLOCK_NMI_SAFE_BROKEN))
  74 #define LTTNG_USE_NMI_SAFE_CLOCK
  75 #endif
  76
  77 #ifdef LTTNG_USE_NMI_SAFE_CLOCK
  78
  79 DECLARE_PER_CPU(u64, lttng_last_tsc);
  80
  81 /*
  82  * Sometimes called with preemption enabled. Can be interrupted.
  83  */
  84 static inline u64 trace_clock_monotonic_wrapper(void)
  85 {
  86         u64 now, last, result;
  87         u64 *last_tsc_ptr;
  88
  89         /* Use fast nmi-safe monotonic clock provided by the Linux kernel. */
  90         preempt_disable();
  91         last_tsc_ptr = lttng_this_cpu_ptr(&lttng_last_tsc);
  92         last = *last_tsc_ptr;
  93         /*
  94          * Read "last" before "now". It is not strictly required, but it ensures
  95          * that an interrupt coming in won't artificially trigger a case where
  96          * "now" < "last". This kind of situation should only happen if the
  97          * mono_fast time source goes slightly backwards.
  98          */
  99         barrier();
 100         now = ktime_get_mono_fast_ns();
 101         if (U64_MAX / 2 < now - last)
 102                 now = last;
 103         result = cmpxchg64_local(last_tsc_ptr, last, now);
 104         preempt_enable();
 105         if (result == last) {
 106                 /* Update done. */
 107                 return now;
 108         } else {
 109                 /*
 110                  * Update not done, due to concurrent update. We can use
 111                  * "result", since it has been sampled concurrently with our
 112                  * time read, so it should not be far from "now".
 113                  */
 114                 return result;
 115         }
 116 }
 117
 118 #else /* #ifdef LTTNG_USE_NMI_SAFE_CLOCK */
 119 static inline u64 trace_clock_monotonic_wrapper(void)
 120 {
 121         ktime_t ktime;
 122
 123         /*
 124          * Refuse to trace from NMIs with this wrapper, because an NMI could
 125          * nest over the xtime write seqlock and deadlock.
 126          */
 127         if (in_nmi())
 128                 return (u64) -EIO;
 129
 130         ktime = ktime_get();
 131         return ktime_to_ns(ktime);
 132 }
 133 #endif /* #else #ifdef LTTNG_USE_NMI_SAFE_CLOCK */
 134
 135 static inline u64 trace_clock_read64_monotonic(void)
 136 {
 137         return (u64) trace_clock_monotonic_wrapper();
 138 }
 139
 140 static inline u64 trace_clock_freq_monotonic(void)
 141 {
 142         return (u64) NSEC_PER_SEC;
 143 }
 144
 145 static inline int trace_clock_uuid_monotonic(char *uuid)
 146 {
 147         return wrapper_get_bootid(uuid);
 148 }
 149
 150 static inline const char *trace_clock_name_monotonic(void)
 151 {
 152         return "monotonic";
 153 }
 154
 155 static inline const char *trace_clock_description_monotonic(void)
 156 {
 157         return "Monotonic Clock";
 158 }
 159
 160 #ifdef LTTNG_USE_NMI_SAFE_CLOCK
 161 static inline int get_trace_clock(void)
 162 {
 163         printk_once(KERN_WARNING "LTTng: Using mainline kernel monotonic fast clock, which is NMI-safe.\n");
 164         return 0;
 165 }
 166 #else /* #ifdef LTTNG_USE_NMI_SAFE_CLOCK */
 167 static inline int get_trace_clock(void)
 168 {
 169         printk_once(KERN_WARNING "LTTng: Using mainline kernel monotonic clock. NMIs will not be traced.\n");
 170         return 0;
 171 }
 172 #endif /* #else #ifdef LTTNG_USE_NMI_SAFE_CLOCK */
 173
 174 static inline void put_trace_clock(void)
 175 {
 176 }
 177
 178 static inline u64 trace_clock_read64(void)
 179 {
 180         struct lttng_trace_clock *ltc = READ_ONCE(lttng_trace_clock);
 181
 182         if (likely(!ltc)) {
 183                 return trace_clock_read64_monotonic();
 184         } else {
 185                 read_barrier_depends(); /* load ltc before content */
 186                 return ltc->read64();
 187         }
 188 }
 189
 190 static inline u64 trace_clock_freq(void)
 191 {
 192         struct lttng_trace_clock *ltc = READ_ONCE(lttng_trace_clock);
 193
 194         if (!ltc) {
 195                 return trace_clock_freq_monotonic();
 196         } else {
 197                 read_barrier_depends(); /* load ltc before content */
 198                 return ltc->freq();
 199         }
 200 }
 201
 202 static inline int trace_clock_uuid(char *uuid)
 203 {
 204         struct lttng_trace_clock *ltc = READ_ONCE(lttng_trace_clock);
 205
 206         read_barrier_depends(); /* load ltc before content */
 207         /* Use default UUID cb when NULL */
 208         if (!ltc || !ltc->uuid) {
 209                 return trace_clock_uuid_monotonic(uuid);
 210         } else {
 211                 return ltc->uuid(uuid);
 212         }
 213 }
 214
 215 static inline const char *trace_clock_name(void)
 216 {
 217         struct lttng_trace_clock *ltc = READ_ONCE(lttng_trace_clock);
 218
 219         if (!ltc) {
 220                 return trace_clock_name_monotonic();
 221         } else {
 222                 read_barrier_depends(); /* load ltc before content */
 223                 return ltc->name();
 224         }
 225 }
 226
 227 static inline const char *trace_clock_description(void)
 228 {
 229         struct lttng_trace_clock *ltc = READ_ONCE(lttng_trace_clock);
 230
 231         if (!ltc) {
 232                 return trace_clock_description_monotonic();
 233         } else {
 234                 read_barrier_depends(); /* load ltc before content */
 235                 return ltc->description();
 236         }
 237 }
 238
 239 #endif /* CONFIG_HAVE_TRACE_CLOCK */
 240
 241 #endif /* _LTTNG_TRACE_CLOCK_H */