-/*
- * Copyright (C) 2011 Mathieu Desnoyers (mathieu.desnoyers@efficios.com)
+/* SPDX-License-Identifier: (GPL-2.0 or LGPL-2.1)
+ *
+ * wrapper/trace-clock.h
*
* Contains LTTng trace clock mapping to LTTng trace clock or mainline monotonic
* clock. This wrapper depends on CONFIG_HIGH_RES_TIMERS=y.
*
- * Dual LGPL v2.1/GPL v2 license.
+ * Copyright (C) 2011-2012 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
*/
#ifndef _LTTNG_TRACE_CLOCK_H
#include <linux/ktime.h>
#include <linux/time.h>
#include <linux/hrtimer.h>
-#include "random.h"
+#include <linux/percpu.h>
+#include <linux/version.h>
+#include <asm/local.h>
+#include <lttng-kernel-version.h>
+#include <lttng-clock.h>
+#include <wrapper/compiler.h>
+#include <wrapper/percpu-defs.h>
+#include <wrapper/random.h>
+#include <blacklist/timekeeping.h>
+
+extern struct lttng_trace_clock *lttng_trace_clock;
+
+/*
+ * Upstream Linux commit 27727df240c7 ("Avoid taking lock in NMI path with
+ * CONFIG_DEBUG_TIMEKEEPING") introduces a buggy ktime_get_mono_fast_ns().
+ * This is fixed by patch "timekeeping: Fix __ktime_get_fast_ns() regression".
+ */
+#if (LTTNG_KERNEL_RANGE(4,8,0, 4,8,2) \
+ || LTTNG_KERNEL_RANGE(4,7,4, 4,7,8) \
+ || LTTNG_KERNEL_RANGE(4,4,20, 4,4,25) \
+ || LTTNG_KERNEL_RANGE(4,1,32, 4,1,35))
+#define LTTNG_CLOCK_NMI_SAFE_BROKEN
+#endif
+
+/*
+ * We need clock values to be monotonically increasing per-cpu, which is
+ * not strictly guaranteed by ktime_get_mono_fast_ns(). It is
+ * straightforward to do on architectures with a 64-bit cmpxchg(), but
+ * not so on architectures without 64-bit cmpxchg. For now, only enable
+ * this feature on 64-bit architectures.
+ */
+
+#if (LINUX_VERSION_CODE >= KERNEL_VERSION(3,17,0) \
+ && BITS_PER_LONG == 64 \
+ && !defined(LTTNG_CLOCK_NMI_SAFE_BROKEN))
+#define LTTNG_USE_NMI_SAFE_CLOCK
+#endif
+
+#ifdef LTTNG_USE_NMI_SAFE_CLOCK
+
+DECLARE_PER_CPU(u64, lttng_last_tsc);
+/*
+ * Sometimes called with preemption enabled. Can be interrupted.
+ */
+static inline u64 trace_clock_monotonic_wrapper(void)
+{
+ u64 now, last, result;
+ u64 *last_tsc_ptr;
+
+ /* Use fast nmi-safe monotonic clock provided by the Linux kernel. */
+ preempt_disable();
+ last_tsc_ptr = lttng_this_cpu_ptr(<tng_last_tsc);
+ last = *last_tsc_ptr;
+ /*
+ * Read "last" before "now". It is not strictly required, but it ensures
+ * that an interrupt coming in won't artificially trigger a case where
+ * "now" < "last". This kind of situation should only happen if the
+ * mono_fast time source goes slightly backwards.
+ */
+ barrier();
+ now = ktime_get_mono_fast_ns();
+ if (U64_MAX / 2 < now - last)
+ now = last;
+ result = cmpxchg64_local(last_tsc_ptr, last, now);
+ preempt_enable();
+ if (result == last) {
+ /* Update done. */
+ return now;
+ } else {
+ /*
+ * Update not done, due to concurrent update. We can use
+ * "result", since it has been sampled concurrently with our
+ * time read, so it should not be far from "now".
+ */
+ return result;
+ }
+}
+
+#else /* #ifdef LTTNG_USE_NMI_SAFE_CLOCK */
static inline u64 trace_clock_monotonic_wrapper(void)
{
ktime_t ktime;
return (u64) -EIO;
ktime = ktime_get();
- return (u64) ktime.tv64;
+ return ktime_to_ns(ktime);
}
+#endif /* #else #ifdef LTTNG_USE_NMI_SAFE_CLOCK */
-static inline u32 trace_clock_read32(void)
+static inline u64 trace_clock_read64_monotonic(void)
+{
+ return (u64) trace_clock_monotonic_wrapper();
+}
+
+static inline u64 trace_clock_freq_monotonic(void)
+{
+ return (u64) NSEC_PER_SEC;
+}
+
+static inline int trace_clock_uuid_monotonic(char *uuid)
+{
+ return wrapper_get_bootid(uuid);
+}
+
+static inline const char *trace_clock_name_monotonic(void)
+{
+ return "monotonic";
+}
+
+static inline const char *trace_clock_description_monotonic(void)
+{
+ return "Monotonic Clock";
+}
+
+#ifdef LTTNG_USE_NMI_SAFE_CLOCK
+static inline int get_trace_clock(void)
+{
+ printk_once(KERN_WARNING "LTTng: Using mainline kernel monotonic fast clock, which is NMI-safe.\n");
+ return 0;
+}
+#else /* #ifdef LTTNG_USE_NMI_SAFE_CLOCK */
+static inline int get_trace_clock(void)
+{
+ printk_once(KERN_WARNING "LTTng: Using mainline kernel monotonic clock. NMIs will not be traced.\n");
+ return 0;
+}
+#endif /* #else #ifdef LTTNG_USE_NMI_SAFE_CLOCK */
+
+static inline void put_trace_clock(void)
{
- return (u32) trace_clock_monotonic_wrapper();
}
static inline u64 trace_clock_read64(void)
{
- return (u64) trace_clock_monotonic_wrapper();
+ struct lttng_trace_clock *ltc = READ_ONCE(lttng_trace_clock);
+
+ if (likely(!ltc)) {
+ return trace_clock_read64_monotonic();
+ } else {
+ read_barrier_depends(); /* load ltc before content */
+ return ltc->read64();
+ }
}
static inline u64 trace_clock_freq(void)
{
- return (u64) NSEC_PER_SEC;
+ struct lttng_trace_clock *ltc = READ_ONCE(lttng_trace_clock);
+
+ if (!ltc) {
+ return trace_clock_freq_monotonic();
+ } else {
+ read_barrier_depends(); /* load ltc before content */
+ return ltc->freq();
+ }
}
static inline int trace_clock_uuid(char *uuid)
{
- return wrapper_get_bootid(uuid);
+ struct lttng_trace_clock *ltc = READ_ONCE(lttng_trace_clock);
+
+ read_barrier_depends(); /* load ltc before content */
+ /* Use default UUID cb when NULL */
+ if (!ltc || !ltc->uuid) {
+ return trace_clock_uuid_monotonic(uuid);
+ } else {
+ return ltc->uuid(uuid);
+ }
}
-static inline int get_trace_clock(void)
+static inline const char *trace_clock_name(void)
{
- /*
- * LTTng: Using mainline kernel monotonic clock. NMIs will not be
- * traced, and expect significant performance degradation compared to
- * the LTTng trace clocks. Integration of the LTTng 0.x trace clocks
- * into LTTng 2.0 is planned in a near future.
- */
- printk(KERN_WARNING "LTTng: Using mainline kernel monotonic clock.\n");
- printk(KERN_WARNING " * NMIs will not be traced,\n");
- printk(KERN_WARNING " * expect significant performance degradation compared to the\n");
- printk(KERN_WARNING " LTTng trace clocks.\n");
- printk(KERN_WARNING "Integration of the LTTng 0.x trace clocks into LTTng 2.0 is planned\n");
- printk(KERN_WARNING "in a near future.\n");
+ struct lttng_trace_clock *ltc = READ_ONCE(lttng_trace_clock);
- return 0;
+ if (!ltc) {
+ return trace_clock_name_monotonic();
+ } else {
+ read_barrier_depends(); /* load ltc before content */
+ return ltc->name();
+ }
}
-static inline void put_trace_clock(void)
+static inline const char *trace_clock_description(void)
{
+ struct lttng_trace_clock *ltc = READ_ONCE(lttng_trace_clock);
+
+ if (!ltc) {
+ return trace_clock_description_monotonic();
+ } else {
+ read_barrier_depends(); /* load ltc before content */
+ return ltc->description();
+ }
}
#endif /* CONFIG_HAVE_TRACE_CLOCK */
projects / lttng-modules.git / blobdiff