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 "percpu-defs.h"
  41 #include "random.h"
  42
  43 #if ((LTTNG_KERNEL_RANGE(3,10,0, 3,10,14) && !LTTNG_RHEL_KERNEL_RANGE(3,10,0,7,0, 3,10,14,0,0)) \
  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 #if (LINUX_VERSION_CODE >= KERNEL_VERSION(3,17,0))
  51
  52 DECLARE_PER_CPU(local_t, lttng_last_tsc);
  53
  54 #if (BITS_PER_LONG == 32)
  55 /*
  56  * Fixup "src_now" using the 32 LSB from "last". We need to handle overflow and
  57  * underflow of the 32nd bit. "last" can be above, below or equal to the 32 LSB
  58  * of "src_now".
  59  */
  60 static inline u64 trace_clock_fixup(u64 src_now, u32 last)
  61 {
  62         u64 now;
  63
  64         now = src_now & 0xFFFFFFFF00000000ULL;
  65         now |= (u64) last;
  66         /* Detect overflow or underflow between now and last. */
  67         if ((src_now & 0x80000000U) && !(last & 0x80000000U)) {
  68                 /*
  69                  * If 32nd bit transitions from 1 to 0, and we move forward in
  70                  * time from "now" to "last", then we have an overflow.
  71                  */
  72                 if (((s32) now - (s32) last) < 0)
  73                         now += 0x0000000100000000ULL;
  74         } else if (!(src_now & 0x80000000U) && (last & 0x80000000U)) {
  75                 /*
  76                  * If 32nd bit transitions from 0 to 1, and we move backward in
  77                  * time from "now" to "last", then we have an underflow.
  78                  */
  79                 if (((s32) now - (s32) last) > 0)
  80                         now -= 0x0000000100000000ULL;
  81         }
  82         return now;
  83 }
  84 #else /* #if (BITS_PER_LONG == 32) */
  85 /*
  86  * The fixup is pretty easy on 64-bit architectures: "last" is a 64-bit
  87  * value, so we can use last directly as current time.
  88  */
  89 static inline u64 trace_clock_fixup(u64 src_now, u64 last)
  90 {
  91         return last;
  92 }
  93 #endif /* #else #if (BITS_PER_LONG == 32) */
  94
  95 /*
  96  * Sometimes called with preemption enabled. Can be interrupted.
  97  */
  98 static inline u64 trace_clock_monotonic_wrapper(void)
  99 {
 100         u64 now;
 101         unsigned long last, result;
 102         local_t *last_tsc;
 103
 104         /* Use fast nmi-safe monotonic clock provided by the Linux kernel. */
 105         preempt_disable();
 106         last_tsc = lttng_this_cpu_ptr(&lttng_last_tsc);
 107         last = local_read(last_tsc);
 108         /*
 109          * Read "last" before "now". It is not strictly required, but it ensures
 110          * that an interrupt coming in won't artificially trigger a case where
 111          * "now" < "last". This kind of situation should only happen if the
 112          * mono_fast time source goes slightly backwards.
 113          */
 114         barrier();
 115         now = ktime_get_mono_fast_ns();
 116         if (((long) now - (long) last) < 0)
 117                 now = trace_clock_fixup(now, last);
 118         result = local_cmpxchg(last_tsc, last, (unsigned long) now);
 119         preempt_enable();
 120         if (result == last) {
 121                 /* Update done. */
 122                 return now;
 123         } else {
 124                 /*
 125                  * Update not done, due to concurrent update. We can use
 126                  * "result", since it has been sampled concurrently with our
 127                  * time read, so it should not be far from "now".
 128                  */
 129                 return trace_clock_fixup(now, result);
 130         }
 131 }
 132
 133 #else /* #if (LINUX_VERSION_CODE >= KERNEL_VERSION(3,17,0)) */
 134 static inline u64 trace_clock_monotonic_wrapper(void)
 135 {
 136         ktime_t ktime;
 137
 138         /*
 139          * Refuse to trace from NMIs with this wrapper, because an NMI could
 140          * nest over the xtime write seqlock and deadlock.
 141          */
 142         if (in_nmi())
 143                 return (u64) -EIO;
 144
 145         ktime = ktime_get();
 146         return ktime_to_ns(ktime);
 147 }
 148 #endif /* #else #if (LINUX_VERSION_CODE >= KERNEL_VERSION(3,17,0)) */
 149
 150 static inline u64 trace_clock_read64_monotonic(void)
 151 {
 152         return (u64) trace_clock_monotonic_wrapper();
 153 }
 154
 155 static inline u64 trace_clock_freq_monotonic(void)
 156 {
 157         return (u64) NSEC_PER_SEC;
 158 }
 159
 160 static inline int trace_clock_uuid_monotonic(char *uuid)
 161 {
 162         return wrapper_get_bootid(uuid);
 163 }
 164
 165 static inline const char *trace_clock_name_monotonic(void)
 166 {
 167         return "monotonic";
 168 }
 169
 170 static inline const char *trace_clock_description_monotonic(void)
 171 {
 172         return "Monotonic Clock";
 173 }
 174
 175 #if (LINUX_VERSION_CODE >= KERNEL_VERSION(3,17,0))
 176 static inline int get_trace_clock(void)
 177 {
 178         printk(KERN_WARNING "LTTng: Using mainline kernel monotonic fast clock, which is NMI-safe.\n");
 179         return 0;
 180 }
 181 #else /* #if (LINUX_VERSION_CODE >= KERNEL_VERSION(3,17,0)) */
 182 static inline int get_trace_clock(void)
 183 {
 184         printk(KERN_WARNING "LTTng: Using mainline kernel monotonic clock. NMIs will not be traced.\n");
 185         return 0;
 186 }
 187 #endif /* #else #if (LINUX_VERSION_CODE >= KERNEL_VERSION(3,17,0)) */
 188
 189 static inline void put_trace_clock(void)
 190 {
 191 }
 192
 193 static inline u64 trace_clock_read64(void)
 194 {
 195         struct lttng_trace_clock *ltc = ACCESS_ONCE(lttng_trace_clock);
 196
 197         if (likely(!ltc)) {
 198                 return trace_clock_read64_monotonic();
 199         } else {
 200                 read_barrier_depends(); /* load ltc before content */
 201                 return ltc->read64();
 202         }
 203 }
 204
 205 static inline u64 trace_clock_freq(void)
 206 {
 207         struct lttng_trace_clock *ltc = ACCESS_ONCE(lttng_trace_clock);
 208
 209         if (!ltc) {
 210                 return trace_clock_freq_monotonic();
 211         } else {
 212                 read_barrier_depends(); /* load ltc before content */
 213                 return ltc->freq();
 214         }
 215 }
 216
 217 static inline int trace_clock_uuid(char *uuid)
 218 {
 219         struct lttng_trace_clock *ltc = ACCESS_ONCE(lttng_trace_clock);
 220
 221         read_barrier_depends(); /* load ltc before content */
 222         /* Use default UUID cb when NULL */
 223         if (!ltc || !ltc->uuid) {
 224                 return trace_clock_uuid_monotonic(uuid);
 225         } else {
 226                 return ltc->uuid(uuid);
 227         }
 228 }
 229
 230 static inline const char *trace_clock_name(void)
 231 {
 232         struct lttng_trace_clock *ltc = ACCESS_ONCE(lttng_trace_clock);
 233
 234         if (!ltc) {
 235                 return trace_clock_name_monotonic();
 236         } else {
 237                 read_barrier_depends(); /* load ltc before content */
 238                 return ltc->name();
 239         }
 240 }
 241
 242 static inline const char *trace_clock_description(void)
 243 {
 244         struct lttng_trace_clock *ltc = ACCESS_ONCE(lttng_trace_clock);
 245
 246         if (!ltc) {
 247                 return trace_clock_description_monotonic();
 248         } else {
 249                 read_barrier_depends(); /* load ltc before content */
 250                 return ltc->description();
 251         }
 252 }
 253
 254 #endif /* CONFIG_HAVE_TRACE_CLOCK */
 255
 256 #endif /* _LTTNG_TRACE_CLOCK_H */