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