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 "percpu-defs.h"
43 #if ((LTTNG_KERNEL_RANGE(3,10,0, 3,10,14) && !LTTNG_RHEL_KERNEL_RANGE(3,10,0,7,0, 3,10,14,0,0)) \
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 * Always called with preemption disabled. 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. */
105 last_tsc
= lttng_this_cpu_ptr(<tng_last_tsc
);
106 last
= local_read(last_tsc
);
108 * Read "last" before "now". It is not strictly required, but it ensures
109 * that an interrupt coming in won't artificially trigger a case where
110 * "now" < "last". This kind of situation should only happen if the
111 * mono_fast time source goes slightly backwards.
114 now
= ktime_get_mono_fast_ns();
115 if (((long) now
- (long) last
) < 0)
116 now
= trace_clock_fixup(now
, last
);
117 result
= local_cmpxchg(last_tsc
, last
, (unsigned long) now
);
118 if (result
== last
) {
123 * Update not done, due to concurrent update. We can use
124 * "result", since it has been sampled concurrently with our
125 * time read, so it should not be far from "now".
127 return trace_clock_fixup(now
, result
);
131 #else /* #if (LINUX_VERSION_CODE >= KERNEL_VERSION(3,17,0)) */
132 static inline u64
trace_clock_monotonic_wrapper(void)
137 * Refuse to trace from NMIs with this wrapper, because an NMI could
138 * nest over the xtime write seqlock and deadlock.
144 return ktime_to_ns(ktime
);
146 #endif /* #else #if (LINUX_VERSION_CODE >= KERNEL_VERSION(3,17,0)) */
148 static inline u64
trace_clock_read64_monotonic(void)
150 return (u64
) trace_clock_monotonic_wrapper();
153 static inline u64
trace_clock_freq_monotonic(void)
155 return (u64
) NSEC_PER_SEC
;
158 static inline int trace_clock_uuid_monotonic(char *uuid
)
160 return wrapper_get_bootid(uuid
);
163 static inline const char *trace_clock_name_monotonic(void)
168 static inline const char *trace_clock_description_monotonic(void)
170 return "Monotonic Clock";
173 #if (LINUX_VERSION_CODE >= KERNEL_VERSION(3,17,0))
174 static inline int get_trace_clock(void)
176 printk(KERN_WARNING
"LTTng: Using mainline kernel monotonic fast clock, which is NMI-safe.\n");
179 #else /* #if (LINUX_VERSION_CODE >= KERNEL_VERSION(3,17,0)) */
180 static inline int get_trace_clock(void)
182 printk(KERN_WARNING
"LTTng: Using mainline kernel monotonic clock. NMIs will not be traced.\n");
185 #endif /* #else #if (LINUX_VERSION_CODE >= KERNEL_VERSION(3,17,0)) */
187 static inline void put_trace_clock(void)
191 static inline u64
trace_clock_read64(void)
193 struct lttng_trace_clock
*ltc
= ACCESS_ONCE(lttng_trace_clock
);
196 return trace_clock_read64_monotonic();
198 read_barrier_depends(); /* load ltc before content */
199 return ltc
->read64();
203 static inline u64
trace_clock_freq(void)
205 struct lttng_trace_clock
*ltc
= ACCESS_ONCE(lttng_trace_clock
);
208 return trace_clock_freq_monotonic();
210 read_barrier_depends(); /* load ltc before content */
215 static inline int trace_clock_uuid(char *uuid
)
217 struct lttng_trace_clock
*ltc
= ACCESS_ONCE(lttng_trace_clock
);
219 read_barrier_depends(); /* load ltc before content */
220 /* Use default UUID cb when NULL */
221 if (!ltc
|| !ltc
->uuid
) {
222 return trace_clock_uuid_monotonic(uuid
);
224 return ltc
->uuid(uuid
);
228 static inline const char *trace_clock_name(void)
230 struct lttng_trace_clock
*ltc
= ACCESS_ONCE(lttng_trace_clock
);
233 return trace_clock_name_monotonic();
235 read_barrier_depends(); /* load ltc before content */
240 static inline const char *trace_clock_description(void)
242 struct lttng_trace_clock
*ltc
= ACCESS_ONCE(lttng_trace_clock
);
245 return trace_clock_description_monotonic();
247 read_barrier_depends(); /* load ltc before content */
248 return ltc
->description();
252 #endif /* CONFIG_HAVE_TRACE_CLOCK */
254 #endif /* _LTTNG_TRACE_CLOCK_H */
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