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(3,10,0,7,0, 3,10,14,0,0)) \
  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 #if (LINUX_VERSION_CODE >= KERNEL_VERSION(3,17,0))
  48
  49 DECLARE_PER_CPU(local_t, lttng_last_tsc);
  50
  51 #if (BITS_PER_LONG == 32)
  52 /*
  53  * Fixup "src_now" using the 32 LSB from "last". We need to handle overflow and
  54  * underflow of the 32nd bit. "last" can be above, below or equal to the 32 LSB
  55  * of "src_now".
  56  */
  57 static inline u64 trace_clock_fixup(u64 src_now, u32 last)
  58 {
  59         u64 now;
  60
  61         now = src_now & 0xFFFFFFFF00000000ULL;
  62         now |= (u64) last;
  63         /* Detect overflow or underflow between now and last. */
  64         if ((src_now & 0x80000000U) && !(last & 0x80000000U)) {
  65                 /*
  66                  * If 32nd bit transitions from 1 to 0, and we move forward in
  67                  * time from "now" to "last", then we have an overflow.
  68                  */
  69                 if (((s32) now - (s32) last) < 0)
  70                         now += 0x0000000100000000ULL;
  71         } else if (!(src_now & 0x80000000U) && (last & 0x80000000U)) {
  72                 /*
  73                  * If 32nd bit transitions from 0 to 1, and we move backward in
  74                  * time from "now" to "last", then we have an underflow.
  75                  */
  76                 if (((s32) now - (s32) last) > 0)
  77                         now -= 0x0000000100000000ULL;
  78         }
  79         return now;
  80 }
  81 #else /* #if (BITS_PER_LONG == 32) */
  82 /*
  83  * The fixup is pretty easy on 64-bit architectures: "last" is a 64-bit
  84  * value, so we can use last directly as current time.
  85  */
  86 static inline u64 trace_clock_fixup(u64 src_now, u64 last)
  87 {
  88         return last;
  89 }
  90 #endif /* #else #if (BITS_PER_LONG == 32) */
  91
  92 /*
  93  * Always called with preemption disabled. Can be interrupted.
  94  */
  95 static inline u64 trace_clock_monotonic_wrapper(void)
  96 {
  97         u64 now;
  98         unsigned long last, result;
  99         local_t *last_tsc;
 100
 101         /* Use fast nmi-safe monotonic clock provided by the Linux kernel. */
 102         last_tsc = lttng_this_cpu_ptr(&lttng_last_tsc);
 103         last = local_read(last_tsc);
 104         /*
 105          * Read "last" before "now". It is not strictly required, but it ensures
 106          * that an interrupt coming in won't artificially trigger a case where
 107          * "now" < "last". This kind of situation should only happen if the
 108          * mono_fast time source goes slightly backwards.
 109          */
 110         barrier();
 111         now = ktime_get_mono_fast_ns();
 112         if (((long) now - (long) last) < 0)
 113                 now = trace_clock_fixup(now, last);
 114         result = local_cmpxchg(last_tsc, last, (unsigned long) now);
 115         if (result == last) {
 116                 /* Update done. */
 117                 return now;
 118         } else {
 119                 /*
 120                  * Update not done, due to concurrent update. We can use
 121                  * "result", since it has been sampled concurrently with our
 122                  * time read, so it should not be far from "now".
 123                  */
 124                 return trace_clock_fixup(now, result);
 125         }
 126 }
 127
 128 #else /* #if (LINUX_VERSION_CODE >= KERNEL_VERSION(3,17,0)) */
 129 static inline u64 trace_clock_monotonic_wrapper(void)
 130 {
 131         ktime_t ktime;
 132
 133         /*
 134          * Refuse to trace from NMIs with this wrapper, because an NMI could
 135          * nest over the xtime write seqlock and deadlock.
 136          */
 137         if (in_nmi())
 138                 return (u64) -EIO;
 139
 140         ktime = ktime_get();
 141         return ktime_to_ns(ktime);
 142 }
 143 #endif /* #else #if (LINUX_VERSION_CODE >= KERNEL_VERSION(3,17,0)) */
 144
 145 static inline u64 trace_clock_read64(void)
 146 {
 147         return (u64) trace_clock_monotonic_wrapper();
 148 }
 149
 150 static inline u64 trace_clock_freq(void)
 151 {
 152         return (u64) NSEC_PER_SEC;
 153 }
 154
 155 static inline int trace_clock_uuid(char *uuid)
 156 {
 157         return wrapper_get_bootid(uuid);
 158 }
 159
 160 #if (LINUX_VERSION_CODE >= KERNEL_VERSION(3,17,0))
 161 static inline int get_trace_clock(void)
 162 {
 163         printk(KERN_WARNING "LTTng: Using mainline kernel monotonic fast clock, which is NMI-safe.\n");
 164         return 0;
 165 }
 166 #else /* #if (LINUX_VERSION_CODE >= KERNEL_VERSION(3,17,0)) */
 167 static inline int get_trace_clock(void)
 168 {
 169         printk(KERN_WARNING "LTTng: Using mainline kernel monotonic clock. NMIs will not be traced.\n");
 170         return 0;
 171 }
 172 #endif /* #else #if (LINUX_VERSION_CODE >= KERNEL_VERSION(3,17,0)) */
 173
 174 static inline void put_trace_clock(void)
 175 {
 176 }
 177
 178 #endif /* CONFIG_HAVE_TRACE_CLOCK */
 179
 180 #endif /* _LTTNG_TRACE_CLOCK_H */