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 "percpu-defs.h"
42 #if LTTNG_KERNEL_RANGE(3,10,0, 3,10,14) || LTTNG_KERNEL_RANGE(3,11,0, 3,11,3)
43 #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."
46 #if (LINUX_VERSION_CODE >= KERNEL_VERSION(3,17,0))
48 DECLARE_PER_CPU(local_t
, lttng_last_tsc
);
50 #if (BITS_PER_LONG == 32)
52 * Fixup "src_now" using the 32 LSB from "last". We need to handle overflow and
53 * underflow of the 32nd bit. "last" can be above, below or equal to the 32 LSB
56 static inline u64
trace_clock_fixup(u64 src_now
, u32 last
)
60 now
= src_now
& 0xFFFFFFFF00000000ULL
;
62 /* Detect overflow or underflow between now and last. */
63 if ((src_now
& 0x80000000U
) && !(last
& 0x80000000U
)) {
65 * If 32nd bit transitions from 1 to 0, and we move forward in
66 * time from "now" to "last", then we have an overflow.
68 if (((s32
) now
- (s32
) last
) < 0)
69 now
+= 0x0000000100000000ULL
;
70 } else if (!(src_now
& 0x80000000U
) && (last
& 0x80000000U
)) {
72 * If 32nd bit transitions from 0 to 1, and we move backward in
73 * time from "now" to "last", then we have an underflow.
75 if (((s32
) now
- (s32
) last
) > 0)
76 now
-= 0x0000000100000000ULL
;
80 #else /* #if (BITS_PER_LONG == 32) */
82 * The fixup is pretty easy on 64-bit architectures: "last" is a 64-bit
83 * value, so we can use last directly as current time.
85 static inline u64
trace_clock_fixup(u64 src_now
, u64 last
)
89 #endif /* #else #if (BITS_PER_LONG == 32) */
92 * Always called with preemption disabled. Can be interrupted.
94 static inline u64
trace_clock_monotonic_wrapper(void)
97 unsigned long last
, result
;
100 /* Use fast nmi-safe monotonic clock provided by the Linux kernel. */
101 last_tsc
= lttng_this_cpu_ptr(<tng_last_tsc
);
102 last
= local_read(last_tsc
);
104 * Read "last" before "now". It is not strictly required, but it ensures
105 * that an interrupt coming in won't artificially trigger a case where
106 * "now" < "last". This kind of situation should only happen if the
107 * mono_fast time source goes slightly backwards.
110 now
= ktime_get_mono_fast_ns();
111 if (((long) now
- (long) last
) < 0)
112 now
= trace_clock_fixup(now
, last
);
113 result
= local_cmpxchg(last_tsc
, last
, (unsigned long) now
);
114 if (result
== last
) {
119 * Update not done, due to concurrent update. We can use
120 * "result", since it has been sampled concurrently with our
121 * time read, so it should not be far from "now".
123 return trace_clock_fixup(now
, result
);
127 #else /* #if (LINUX_VERSION_CODE >= KERNEL_VERSION(3,17,0)) */
128 static inline u64
trace_clock_monotonic_wrapper(void)
133 * Refuse to trace from NMIs with this wrapper, because an NMI could
134 * nest over the xtime write seqlock and deadlock.
140 return ktime_to_ns(ktime
);
142 #endif /* #else #if (LINUX_VERSION_CODE >= KERNEL_VERSION(3,17,0)) */
144 static inline u64
trace_clock_read64(void)
146 return (u64
) trace_clock_monotonic_wrapper();
149 static inline u64
trace_clock_freq(void)
151 return (u64
) NSEC_PER_SEC
;
154 static inline int trace_clock_uuid(char *uuid
)
156 return wrapper_get_bootid(uuid
);
159 #if (LINUX_VERSION_CODE >= KERNEL_VERSION(3,17,0))
160 static inline int get_trace_clock(void)
162 printk(KERN_WARNING
"LTTng: Using mainline kernel monotonic fast clock, which is NMI-safe.\n");
165 #else /* #if (LINUX_VERSION_CODE >= KERNEL_VERSION(3,17,0)) */
166 static inline int get_trace_clock(void)
168 printk(KERN_WARNING
"LTTng: Using mainline kernel monotonic clock. NMIs will not be traced.\n");
171 #endif /* #else #if (LINUX_VERSION_CODE >= KERNEL_VERSION(3,17,0)) */
173 static inline void put_trace_clock(void)
177 #endif /* CONFIG_HAVE_TRACE_CLOCK */
179 #endif /* _LTTNG_TRACE_CLOCK_H */
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