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, 4,8,1) \
  56         || LTTNG_KERNEL_RANGE(4,7,4, 4,7,7) \
  57         || LTTNG_KERNEL_RANGE(4,4,20, 4,4,24) \
  58         || LTTNG_KERNEL_RANGE(4,1,32, 4,1,34))
  59 #define LTTNG_CLOCK_NMI_SAFE_BROKEN
  60 #endif
  61
  62 #if (LINUX_VERSION_CODE >= KERNEL_VERSION(3,17,0) \
  63         && !defined(LTTNG_CLOCK_NMI_SAFE_BROKEN))
  64
  65 DECLARE_PER_CPU(local_t, lttng_last_tsc);
  66
  67 #if (BITS_PER_LONG == 32)
  68 /*
  69  * Fixup "src_now" using the 32 LSB from "last". We need to handle overflow and
  70  * underflow of the 32nd bit. "last" can be above, below or equal to the 32 LSB
  71  * of "src_now".
  72  */
  73 static inline u64 trace_clock_fixup(u64 src_now, u32 last)
  74 {
  75         u64 now;
  76
  77         now = src_now & 0xFFFFFFFF00000000ULL;
  78         now |= (u64) last;
  79         /* Detect overflow or underflow between now and last. */
  80         if ((src_now & 0x80000000U) && !(last & 0x80000000U)) {
  81                 /*
  82                  * If 32nd bit transitions from 1 to 0, and we move forward in
  83                  * time from "now" to "last", then we have an overflow.
  84                  */
  85                 if (((s32) now - (s32) last) < 0)
  86                         now += 0x0000000100000000ULL;
  87         } else if (!(src_now & 0x80000000U) && (last & 0x80000000U)) {
  88                 /*
  89                  * If 32nd bit transitions from 0 to 1, and we move backward in
  90                  * time from "now" to "last", then we have an underflow.
  91                  */
  92                 if (((s32) now - (s32) last) > 0)
  93                         now -= 0x0000000100000000ULL;
  94         }
  95         return now;
  96 }
  97 #else /* #if (BITS_PER_LONG == 32) */
  98 /*
  99  * The fixup is pretty easy on 64-bit architectures: "last" is a 64-bit
 100  * value, so we can use last directly as current time.
 101  */
 102 static inline u64 trace_clock_fixup(u64 src_now, u64 last)
 103 {
 104         return last;
 105 }
 106 #endif /* #else #if (BITS_PER_LONG == 32) */
 107
 108 /*
 109  * Sometimes called with preemption enabled. Can be interrupted.
 110  */
 111 static inline u64 trace_clock_monotonic_wrapper(void)
 112 {
 113         u64 now;
 114         unsigned long last, result;
 115         local_t *last_tsc;
 116
 117         /* Use fast nmi-safe monotonic clock provided by the Linux kernel. */
 118         preempt_disable();
 119         last_tsc = lttng_this_cpu_ptr(&lttng_last_tsc);
 120         last = local_read(last_tsc);
 121         /*
 122          * Read "last" before "now". It is not strictly required, but it ensures
 123          * that an interrupt coming in won't artificially trigger a case where
 124          * "now" < "last". This kind of situation should only happen if the
 125          * mono_fast time source goes slightly backwards.
 126          */
 127         barrier();
 128         now = ktime_get_mono_fast_ns();
 129         if (((long) now - (long) last) < 0)
 130                 now = trace_clock_fixup(now, last);
 131         result = local_cmpxchg(last_tsc, last, (unsigned long) now);
 132         preempt_enable();
 133         if (result == last) {
 134                 /* Update done. */
 135                 return now;
 136         } else {
 137                 /*
 138                  * Update not done, due to concurrent update. We can use
 139                  * "result", since it has been sampled concurrently with our
 140                  * time read, so it should not be far from "now".
 141                  */
 142                 return trace_clock_fixup(now, result);
 143         }
 144 }
 145
 146 #else /* #if (LINUX_VERSION_CODE >= KERNEL_VERSION(3,17,0)) */
 147 static inline u64 trace_clock_monotonic_wrapper(void)
 148 {
 149         ktime_t ktime;
 150
 151         /*
 152          * Refuse to trace from NMIs with this wrapper, because an NMI could
 153          * nest over the xtime write seqlock and deadlock.
 154          */
 155         if (in_nmi())
 156                 return (u64) -EIO;
 157
 158         ktime = ktime_get();
 159         return ktime_to_ns(ktime);
 160 }
 161 #endif /* #else #if (LINUX_VERSION_CODE >= KERNEL_VERSION(3,17,0)) */
 162
 163 static inline u64 trace_clock_read64_monotonic(void)
 164 {
 165         return (u64) trace_clock_monotonic_wrapper();
 166 }
 167
 168 static inline u64 trace_clock_freq_monotonic(void)
 169 {
 170         return (u64) NSEC_PER_SEC;
 171 }
 172
 173 static inline int trace_clock_uuid_monotonic(char *uuid)
 174 {
 175         return wrapper_get_bootid(uuid);
 176 }
 177
 178 static inline const char *trace_clock_name_monotonic(void)
 179 {
 180         return "monotonic";
 181 }
 182
 183 static inline const char *trace_clock_description_monotonic(void)
 184 {
 185         return "Monotonic Clock";
 186 }
 187
 188 #if (LINUX_VERSION_CODE >= KERNEL_VERSION(3,17,0))
 189 static inline int get_trace_clock(void)
 190 {
 191         printk_once(KERN_WARNING "LTTng: Using mainline kernel monotonic fast clock, which is NMI-safe.\n");
 192         return 0;
 193 }
 194 #else /* #if (LINUX_VERSION_CODE >= KERNEL_VERSION(3,17,0)) */
 195 static inline int get_trace_clock(void)
 196 {
 197         printk_once(KERN_WARNING "LTTng: Using mainline kernel monotonic clock. NMIs will not be traced.\n");
 198         return 0;
 199 }
 200 #endif /* #else #if (LINUX_VERSION_CODE >= KERNEL_VERSION(3,17,0)) */
 201
 202 static inline void put_trace_clock(void)
 203 {
 204 }
 205
 206 static inline u64 trace_clock_read64(void)
 207 {
 208         struct lttng_trace_clock *ltc = ACCESS_ONCE(lttng_trace_clock);
 209
 210         if (likely(!ltc)) {
 211                 return trace_clock_read64_monotonic();
 212         } else {
 213                 read_barrier_depends(); /* load ltc before content */
 214                 return ltc->read64();
 215         }
 216 }
 217
 218 static inline u64 trace_clock_freq(void)
 219 {
 220         struct lttng_trace_clock *ltc = ACCESS_ONCE(lttng_trace_clock);
 221
 222         if (!ltc) {
 223                 return trace_clock_freq_monotonic();
 224         } else {
 225                 read_barrier_depends(); /* load ltc before content */
 226                 return ltc->freq();
 227         }
 228 }
 229
 230 static inline int trace_clock_uuid(char *uuid)
 231 {
 232         struct lttng_trace_clock *ltc = ACCESS_ONCE(lttng_trace_clock);
 233
 234         read_barrier_depends(); /* load ltc before content */
 235         /* Use default UUID cb when NULL */
 236         if (!ltc || !ltc->uuid) {
 237                 return trace_clock_uuid_monotonic(uuid);
 238         } else {
 239                 return ltc->uuid(uuid);
 240         }
 241 }
 242
 243 static inline const char *trace_clock_name(void)
 244 {
 245         struct lttng_trace_clock *ltc = ACCESS_ONCE(lttng_trace_clock);
 246
 247         if (!ltc) {
 248                 return trace_clock_name_monotonic();
 249         } else {
 250                 read_barrier_depends(); /* load ltc before content */
 251                 return ltc->name();
 252         }
 253 }
 254
 255 static inline const char *trace_clock_description(void)
 256 {
 257         struct lttng_trace_clock *ltc = ACCESS_ONCE(lttng_trace_clock);
 258
 259         if (!ltc) {
 260                 return trace_clock_description_monotonic();
 261         } else {
 262                 read_barrier_depends(); /* load ltc before content */
 263                 return ltc->description();
 264         }
 265 }
 266
 267 #endif /* CONFIG_HAVE_TRACE_CLOCK */
 268
 269 #endif /* _LTTNG_TRACE_CLOCK_H */