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 "percpu-defs.h"
  40 #include "random.h"
  41
  42 #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)) \
  43         || LTTNG_KERNEL_RANGE(3,11,0, 3,11,3))
  44 #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."
  45 #endif
  46
  47 /*
  48  * Upstream Linux commit 27727df240c7 ("Avoid taking lock in NMI path with
  49  * CONFIG_DEBUG_TIMEKEEPING") introduces a buggy ktime_get_mono_fast_ns().
  50  * This is fixed by patch "timekeeping: Fix __ktime_get_fast_ns() regression".
  51  */
  52 #if (LTTNG_KERNEL_RANGE(4,8,0, 4,8,2) \
  53         || LTTNG_KERNEL_RANGE(4,7,4, 4,7,8) \
  54         || LTTNG_KERNEL_RANGE(4,4,20, 4,4,25) \
  55         || LTTNG_KERNEL_RANGE(4,1,32, 4,1,35))
  56 #define LTTNG_CLOCK_NMI_SAFE_BROKEN
  57 #endif
  58
  59 #if (LINUX_VERSION_CODE >= KERNEL_VERSION(3,17,0) \
  60         && !defined(LTTNG_CLOCK_NMI_SAFE_BROKEN))
  61
  62 DECLARE_PER_CPU(local_t, lttng_last_tsc);
  63
  64 #if (BITS_PER_LONG == 32)
  65 /*
  66  * Fixup "src_now" using the 32 LSB from "last". We need to handle overflow and
  67  * underflow of the 32nd bit. "last" can be above, below or equal to the 32 LSB
  68  * of "src_now".
  69  */
  70 static inline u64 trace_clock_fixup(u64 src_now, u32 last)
  71 {
  72         u64 now;
  73
  74         now = src_now & 0xFFFFFFFF00000000ULL;
  75         now |= (u64) last;
  76         /* Detect overflow or underflow between now and last. */
  77         if ((src_now & 0x80000000U) && !(last & 0x80000000U)) {
  78                 /*
  79                  * If 32nd bit transitions from 1 to 0, and we move forward in
  80                  * time from "now" to "last", then we have an overflow.
  81                  */
  82                 if (((s32) now - (s32) last) < 0)
  83                         now += 0x0000000100000000ULL;
  84         } else if (!(src_now & 0x80000000U) && (last & 0x80000000U)) {
  85                 /*
  86                  * If 32nd bit transitions from 0 to 1, and we move backward in
  87                  * time from "now" to "last", then we have an underflow.
  88                  */
  89                 if (((s32) now - (s32) last) > 0)
  90                         now -= 0x0000000100000000ULL;
  91         }
  92         return now;
  93 }
  94 #else /* #if (BITS_PER_LONG == 32) */
  95 /*
  96  * The fixup is pretty easy on 64-bit architectures: "last" is a 64-bit
  97  * value, so we can use last directly as current time.
  98  */
  99 static inline u64 trace_clock_fixup(u64 src_now, u64 last)
 100 {
 101         return last;
 102 }
 103 #endif /* #else #if (BITS_PER_LONG == 32) */
 104
 105 /*
 106  * Sometimes called with preemption enabled. Can be interrupted.
 107  */
 108 static inline u64 trace_clock_monotonic_wrapper(void)
 109 {
 110         u64 now;
 111         unsigned long last, result;
 112         local_t *last_tsc;
 113
 114         /* Use fast nmi-safe monotonic clock provided by the Linux kernel. */
 115         preempt_disable();
 116         last_tsc = lttng_this_cpu_ptr(&lttng_last_tsc);
 117         last = local_read(last_tsc);
 118         /*
 119          * Read "last" before "now". It is not strictly required, but it ensures
 120          * that an interrupt coming in won't artificially trigger a case where
 121          * "now" < "last". This kind of situation should only happen if the
 122          * mono_fast time source goes slightly backwards.
 123          */
 124         barrier();
 125         now = ktime_get_mono_fast_ns();
 126         if (((long) now - (long) last) < 0)
 127                 now = trace_clock_fixup(now, last);
 128         result = local_cmpxchg(last_tsc, last, (unsigned long) now);
 129         preempt_enable();
 130         if (result == last) {
 131                 /* Update done. */
 132                 return now;
 133         } else {
 134                 /*
 135                  * Update not done, due to concurrent update. We can use
 136                  * "result", since it has been sampled concurrently with our
 137                  * time read, so it should not be far from "now".
 138                  */
 139                 return trace_clock_fixup(now, result);
 140         }
 141 }
 142
 143 #else /* #if (LINUX_VERSION_CODE >= KERNEL_VERSION(3,17,0)) */
 144 static inline u64 trace_clock_monotonic_wrapper(void)
 145 {
 146         ktime_t ktime;
 147
 148         /*
 149          * Refuse to trace from NMIs with this wrapper, because an NMI could
 150          * nest over the xtime write seqlock and deadlock.
 151          */
 152         if (in_nmi())
 153                 return (u64) -EIO;
 154
 155         ktime = ktime_get();
 156         return ktime_to_ns(ktime);
 157 }
 158 #endif /* #else #if (LINUX_VERSION_CODE >= KERNEL_VERSION(3,17,0)) */
 159
 160 static inline u64 trace_clock_read64(void)
 161 {
 162         return (u64) trace_clock_monotonic_wrapper();
 163 }
 164
 165 static inline u64 trace_clock_freq(void)
 166 {
 167         return (u64) NSEC_PER_SEC;
 168 }
 169
 170 static inline int trace_clock_uuid(char *uuid)
 171 {
 172         return wrapper_get_bootid(uuid);
 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 #endif /* CONFIG_HAVE_TRACE_CLOCK */
 194
 195 #endif /* _LTTNG_TRACE_CLOCK_H */