1 #ifndef _LTTNG_TRACE_CLOCK_H
2 #define _LTTNG_TRACE_CLOCK_H
5 * wrapper/trace-clock.h
7 * Contains LTTng trace clock mapping to LTTng trace clock or mainline monotonic
8 * clock. This wrapper depends on CONFIG_HIGH_RES_TIMERS=y.
10 * Copyright (C) 2011-2012 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
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.
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.
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
27 #ifdef CONFIG_HAVE_TRACE_CLOCK
28 #include <linux/trace-clock.h>
29 #else /* CONFIG_HAVE_TRACE_CLOCK */
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>
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."
48 extern struct lttng_trace_clock
*lttng_trace_clock
;
50 #if (LINUX_VERSION_CODE >= KERNEL_VERSION(3,17,0))
52 DECLARE_PER_CPU(local_t
, lttng_last_tsc
);
54 #if (BITS_PER_LONG == 32)
56 * Fixup "src_now" using the 32 LSB from "last". We need to handle overflow and
57 * underflow of the 32nd bit. "last" can be above, below or equal to the 32 LSB
60 static inline u64
trace_clock_fixup(u64 src_now
, u32 last
)
64 now
= src_now
& 0xFFFFFFFF00000000ULL
;
66 /* Detect overflow or underflow between now and last. */
67 if ((src_now
& 0x80000000U
) && !(last
& 0x80000000U
)) {
69 * If 32nd bit transitions from 1 to 0, and we move forward in
70 * time from "now" to "last", then we have an overflow.
72 if (((s32
) now
- (s32
) last
) < 0)
73 now
+= 0x0000000100000000ULL
;
74 } else if (!(src_now
& 0x80000000U
) && (last
& 0x80000000U
)) {
76 * If 32nd bit transitions from 0 to 1, and we move backward in
77 * time from "now" to "last", then we have an underflow.
79 if (((s32
) now
- (s32
) last
) > 0)
80 now
-= 0x0000000100000000ULL
;
84 #else /* #if (BITS_PER_LONG == 32) */
86 * The fixup is pretty easy on 64-bit architectures: "last" is a 64-bit
87 * value, so we can use last directly as current time.
89 static inline u64
trace_clock_fixup(u64 src_now
, u64 last
)
93 #endif /* #else #if (BITS_PER_LONG == 32) */
96 * Sometimes called with preemption enabled. Can be interrupted.
98 static inline u64
trace_clock_monotonic_wrapper(void)
101 unsigned long last
, result
;
104 /* Use fast nmi-safe monotonic clock provided by the Linux kernel. */
106 last_tsc
= lttng_this_cpu_ptr(<tng_last_tsc
);
107 last
= local_read(last_tsc
);
109 * Read "last" before "now". It is not strictly required, but it ensures
110 * that an interrupt coming in won't artificially trigger a case where
111 * "now" < "last". This kind of situation should only happen if the
112 * mono_fast time source goes slightly backwards.
115 now
= ktime_get_mono_fast_ns();
116 if (((long) now
- (long) last
) < 0)
117 now
= trace_clock_fixup(now
, last
);
118 result
= local_cmpxchg(last_tsc
, last
, (unsigned long) now
);
120 if (result
== last
) {
125 * Update not done, due to concurrent update. We can use
126 * "result", since it has been sampled concurrently with our
127 * time read, so it should not be far from "now".
129 return trace_clock_fixup(now
, result
);
133 #else /* #if (LINUX_VERSION_CODE >= KERNEL_VERSION(3,17,0)) */
134 static inline u64
trace_clock_monotonic_wrapper(void)
139 * Refuse to trace from NMIs with this wrapper, because an NMI could
140 * nest over the xtime write seqlock and deadlock.
146 return ktime_to_ns(ktime
);
148 #endif /* #else #if (LINUX_VERSION_CODE >= KERNEL_VERSION(3,17,0)) */
150 static inline u64
trace_clock_read64_monotonic(void)
152 return (u64
) trace_clock_monotonic_wrapper();
155 static inline u64
trace_clock_freq_monotonic(void)
157 return (u64
) NSEC_PER_SEC
;
160 static inline int trace_clock_uuid_monotonic(char *uuid
)
162 return wrapper_get_bootid(uuid
);
165 static inline const char *trace_clock_name_monotonic(void)
170 static inline const char *trace_clock_description_monotonic(void)
172 return "Monotonic Clock";
175 #if (LINUX_VERSION_CODE >= KERNEL_VERSION(3,17,0))
176 static inline int get_trace_clock(void)
178 printk(KERN_WARNING
"LTTng: Using mainline kernel monotonic fast clock, which is NMI-safe.\n");
181 #else /* #if (LINUX_VERSION_CODE >= KERNEL_VERSION(3,17,0)) */
182 static inline int get_trace_clock(void)
184 printk(KERN_WARNING
"LTTng: Using mainline kernel monotonic clock. NMIs will not be traced.\n");
187 #endif /* #else #if (LINUX_VERSION_CODE >= KERNEL_VERSION(3,17,0)) */
189 static inline void put_trace_clock(void)
193 static inline u64
trace_clock_read64(void)
195 struct lttng_trace_clock
*ltc
= ACCESS_ONCE(lttng_trace_clock
);
198 return trace_clock_read64_monotonic();
200 read_barrier_depends(); /* load ltc before content */
201 return ltc
->read64();
205 static inline u64
trace_clock_freq(void)
207 struct lttng_trace_clock
*ltc
= ACCESS_ONCE(lttng_trace_clock
);
210 return trace_clock_freq_monotonic();
212 read_barrier_depends(); /* load ltc before content */
217 static inline int trace_clock_uuid(char *uuid
)
219 struct lttng_trace_clock
*ltc
= ACCESS_ONCE(lttng_trace_clock
);
221 read_barrier_depends(); /* load ltc before content */
222 /* Use default UUID cb when NULL */
223 if (!ltc
|| !ltc
->uuid
) {
224 return trace_clock_uuid_monotonic(uuid
);
226 return ltc
->uuid(uuid
);
230 static inline const char *trace_clock_name(void)
232 struct lttng_trace_clock
*ltc
= ACCESS_ONCE(lttng_trace_clock
);
235 return trace_clock_name_monotonic();
237 read_barrier_depends(); /* load ltc before content */
242 static inline const char *trace_clock_description(void)
244 struct lttng_trace_clock
*ltc
= ACCESS_ONCE(lttng_trace_clock
);
247 return trace_clock_description_monotonic();
249 read_barrier_depends(); /* load ltc before content */
250 return ltc
->description();
254 #endif /* CONFIG_HAVE_TRACE_CLOCK */
256 #endif /* _LTTNG_TRACE_CLOCK_H */
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