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 (LINUX_VERSION_CODE >= KERNEL_VERSION(3,17,0) \
  53         && !LTTNG_KERNEL_RANGE(4,8,0, 4,8,1) \
  54         && !LTTNG_KERNEL_RANGE(4,7,4, 4,7,7) \
  55         && !LTTNG_KERNEL_RANGE(4,4,20, 4,4,24) \
  56         && !LTTNG_KERNEL_RANGE(4,1,32, 4,1,34))
  57
  58 DECLARE_PER_CPU(local_t, lttng_last_tsc);
  59
  60 #if (BITS_PER_LONG == 32)
  61 /*
  62  * Fixup "src_now" using the 32 LSB from "last". We need to handle overflow and
  63  * underflow of the 32nd bit. "last" can be above, below or equal to the 32 LSB
  64  * of "src_now".
  65  */
  66 static inline u64 trace_clock_fixup(u64 src_now, u32 last)
  67 {
  68         u64 now;
  69
  70         now = src_now & 0xFFFFFFFF00000000ULL;
  71         now |= (u64) last;
  72         /* Detect overflow or underflow between now and last. */
  73         if ((src_now & 0x80000000U) && !(last & 0x80000000U)) {
  74                 /*
  75                  * If 32nd bit transitions from 1 to 0, and we move forward in
  76                  * time from "now" to "last", then we have an overflow.
  77                  */
  78                 if (((s32) now - (s32) last) < 0)
  79                         now += 0x0000000100000000ULL;
  80         } else if (!(src_now & 0x80000000U) && (last & 0x80000000U)) {
  81                 /*
  82                  * If 32nd bit transitions from 0 to 1, and we move backward in
  83                  * time from "now" to "last", then we have an underflow.
  84                  */
  85                 if (((s32) now - (s32) last) > 0)
  86                         now -= 0x0000000100000000ULL;
  87         }
  88         return now;
  89 }
  90 #else /* #if (BITS_PER_LONG == 32) */
  91 /*
  92  * The fixup is pretty easy on 64-bit architectures: "last" is a 64-bit
  93  * value, so we can use last directly as current time.
  94  */
  95 static inline u64 trace_clock_fixup(u64 src_now, u64 last)
  96 {
  97         return last;
  98 }
  99 #endif /* #else #if (BITS_PER_LONG == 32) */
 100
 101 /*
 102  * Sometimes called with preemption enabled. Can be interrupted.
 103  */
 104 static inline u64 trace_clock_monotonic_wrapper(void)
 105 {
 106         u64 now;
 107         unsigned long last, result;
 108         local_t *last_tsc;
 109
 110         /* Use fast nmi-safe monotonic clock provided by the Linux kernel. */
 111         preempt_disable();
 112         last_tsc = lttng_this_cpu_ptr(&lttng_last_tsc);
 113         last = local_read(last_tsc);
 114         /*
 115          * Read "last" before "now". It is not strictly required, but it ensures
 116          * that an interrupt coming in won't artificially trigger a case where
 117          * "now" < "last". This kind of situation should only happen if the
 118          * mono_fast time source goes slightly backwards.
 119          */
 120         barrier();
 121         now = ktime_get_mono_fast_ns();
 122         if (((long) now - (long) last) < 0)
 123                 now = trace_clock_fixup(now, last);
 124         result = local_cmpxchg(last_tsc, last, (unsigned long) now);
 125         preempt_enable();
 126         if (result == last) {
 127                 /* Update done. */
 128                 return now;
 129         } else {
 130                 /*
 131                  * Update not done, due to concurrent update. We can use
 132                  * "result", since it has been sampled concurrently with our
 133                  * time read, so it should not be far from "now".
 134                  */
 135                 return trace_clock_fixup(now, result);
 136         }
 137 }
 138
 139 #else /* #if (LINUX_VERSION_CODE >= KERNEL_VERSION(3,17,0)) */
 140 static inline u64 trace_clock_monotonic_wrapper(void)
 141 {
 142         ktime_t ktime;
 143
 144         /*
 145          * Refuse to trace from NMIs with this wrapper, because an NMI could
 146          * nest over the xtime write seqlock and deadlock.
 147          */
 148         if (in_nmi())
 149                 return (u64) -EIO;
 150
 151         ktime = ktime_get();
 152         return ktime_to_ns(ktime);
 153 }
 154 #endif /* #else #if (LINUX_VERSION_CODE >= KERNEL_VERSION(3,17,0)) */
 155
 156 static inline u64 trace_clock_read64(void)
 157 {
 158         return (u64) trace_clock_monotonic_wrapper();
 159 }
 160
 161 static inline u64 trace_clock_freq(void)
 162 {
 163         return (u64) NSEC_PER_SEC;
 164 }
 165
 166 static inline int trace_clock_uuid(char *uuid)
 167 {
 168         return wrapper_get_bootid(uuid);
 169 }
 170
 171 #if (LINUX_VERSION_CODE >= KERNEL_VERSION(3,17,0))
 172 static inline int get_trace_clock(void)
 173 {
 174         printk(KERN_WARNING "LTTng: Using mainline kernel monotonic fast clock, which is NMI-safe.\n");
 175         return 0;
 176 }
 177 #else /* #if (LINUX_VERSION_CODE >= KERNEL_VERSION(3,17,0)) */
 178 static inline int get_trace_clock(void)
 179 {
 180         printk(KERN_WARNING "LTTng: Using mainline kernel monotonic clock. NMIs will not be traced.\n");
 181         return 0;
 182 }
 183 #endif /* #else #if (LINUX_VERSION_CODE >= KERNEL_VERSION(3,17,0)) */
 184
 185 static inline void put_trace_clock(void)
 186 {
 187 }
 188
 189 #endif /* CONFIG_HAVE_TRACE_CLOCK */
 190
 191 #endif /* _LTTNG_TRACE_CLOCK_H */