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 "random.h"
  40
  41 #if LTTNG_KERNEL_RANGE(3,10,0, 3,10,14) || LTTNG_KERNEL_RANGE(3,11,0, 3,11,3)
  42 #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."
  43 #endif
  44
  45 #if (LINUX_VERSION_CODE >= KERNEL_VERSION(3,17,0))
  46
  47 DECLARE_PER_CPU(local_t, lttng_last_tsc);
  48
  49 #if (BITS_PER_LONG == 32)
  50 /*
  51  * Fixup "src_now" using the 32 LSB from "last". We need to handle overflow and
  52  * underflow of the 32nd bit. "last" can be above, below or equal to the 32 LSB
  53  * of "src_now".
  54  */
  55 static inline u64 trace_clock_fixup(u64 src_now, u32 last)
  56 {
  57         u64 now;
  58
  59         now = src_now & 0xFFFFFFFF00000000ULL;
  60         now |= (u64) last;
  61         /* Detect overflow or underflow between now and last. */
  62         if ((src_now & 0x80000000U) && !(last & 0x80000000U)) {
  63                 /*
  64                  * If 32nd bit transitions from 1 to 0, and we move forward in
  65                  * time from "now" to "last", then we have an overflow.
  66                  */
  67                 if (((s32) now - (s32) last) < 0)
  68                         now += 0x0000000100000000ULL;
  69         } else if (!(src_now & 0x80000000U) && (last & 0x80000000U)) {
  70                 /*
  71                  * If 32nd bit transitions from 0 to 1, and we move backward in
  72                  * time from "now" to "last", then we have an underflow.
  73                  */
  74                 if (((s32) now - (s32) last) > 0)
  75                         now -= 0x0000000100000000ULL;
  76         }
  77         return now;
  78 }
  79 #else /* #if (BITS_PER_LONG == 32) */
  80 /*
  81  * The fixup is pretty easy on 64-bit architectures: "last" is a 64-bit
  82  * value, so we can use last directly as current time.
  83  */
  84 static inline u64 trace_clock_fixup(u64 src_now, u64 last)
  85 {
  86         return last;
  87 }
  88 #endif /* #else #if (BITS_PER_LONG == 32) */
  89
  90 /*
  91  * Always called with preemption disabled. Can be interrupted.
  92  */
  93 static inline u64 trace_clock_monotonic_wrapper(void)
  94 {
  95         u64 now;
  96         unsigned long last, result;
  97         local_t *last_tsc;
  98
  99         /* Use fast nmi-safe monotonic clock provided by the Linux kernel. */
 100         last_tsc = &__get_cpu_var(lttng_last_tsc);
 101         last = local_read(last_tsc);
 102         /*
 103          * Read "last" before "now". It is not strictly required, but it ensures
 104          * that an interrupt coming in won't artificially trigger a case where
 105          * "now" < "last". This kind of situation should only happen if the
 106          * mono_fast time source goes slightly backwards.
 107          */
 108         barrier();
 109         now = ktime_get_mono_fast_ns();
 110         if (((long) now - (long) last) < 0)
 111                 now = trace_clock_fixup(now, last);
 112         result = local_cmpxchg(last_tsc, last, (unsigned long) now);
 113         if (result == last) {
 114                 /* Update done. */
 115                 return now;
 116         } else {
 117                 /*
 118                  * Update not done, due to concurrent update. We can use
 119                  * "result", since it has been sampled concurrently with our
 120                  * time read, so it should not be far from "now".
 121                  */
 122                 return trace_clock_fixup(now, result);
 123         }
 124 }
 125
 126 #else /* #if (LINUX_VERSION_CODE >= KERNEL_VERSION(3,17,0)) */
 127 static inline u64 trace_clock_monotonic_wrapper(void)
 128 {
 129         ktime_t ktime;
 130
 131         /*
 132          * Refuse to trace from NMIs with this wrapper, because an NMI could
 133          * nest over the xtime write seqlock and deadlock.
 134          */
 135         if (in_nmi())
 136                 return (u64) -EIO;
 137
 138         ktime = ktime_get();
 139         return ktime_to_ns(ktime);
 140 }
 141 #endif /* #else #if (LINUX_VERSION_CODE >= KERNEL_VERSION(3,17,0)) */
 142
 143 static inline u64 trace_clock_read64(void)
 144 {
 145         return (u64) trace_clock_monotonic_wrapper();
 146 }
 147
 148 static inline u64 trace_clock_freq(void)
 149 {
 150         return (u64) NSEC_PER_SEC;
 151 }
 152
 153 static inline int trace_clock_uuid(char *uuid)
 154 {
 155         return wrapper_get_bootid(uuid);
 156 }
 157
 158 #if (LINUX_VERSION_CODE >= KERNEL_VERSION(3,17,0))
 159 static inline int get_trace_clock(void)
 160 {
 161         printk(KERN_WARNING "LTTng: Using mainline kernel monotonic fast clock, which is NMI-safe.\n");
 162         return 0;
 163 }
 164 #else /* #if (LINUX_VERSION_CODE >= KERNEL_VERSION(3,17,0)) */
 165 static inline int get_trace_clock(void)
 166 {
 167         printk(KERN_WARNING "LTTng: Using mainline kernel monotonic clock. NMIs will not be traced.\n");
 168         return 0;
 169 }
 170 #endif /* #else #if (LINUX_VERSION_CODE >= KERNEL_VERSION(3,17,0)) */
 171
 172 static inline void put_trace_clock(void)
 173 {
 174 }
 175
 176 #endif /* CONFIG_HAVE_TRACE_CLOCK */
 177
 178 #endif /* _LTTNG_TRACE_CLOCK_H */