[lttng-dev] [RFC PATCH lttng-modules] Use 3.16 ktime_get_mono_fast_ns() new API
Mathieu Desnoyers
mathieu.desnoyers at efficios.com
Sun Jul 13 14:15:22 EDT 2014
The new ktime_get_mono_fast_ns() API introduced in kernel 3.16 allows
tracing NMI handlers.
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers at efficios.com>
Cc: Thomas Gleixner <tglx at linutronix.de>
---
Makefile | 2 +-
wrapper/trace-clock.c | 29 ++++++++++++++
wrapper/trace-clock.h | 107 +++++++++++++++++++++++++++++++++++++++++++------
3 files changed, 124 insertions(+), 14 deletions(-)
create mode 100644 wrapper/trace-clock.c
diff --git a/Makefile b/Makefile
index 606b5ec..9935e15 100644
--- a/Makefile
+++ b/Makefile
@@ -21,7 +21,7 @@ lttng-tracer-objs := lttng-events.o lttng-abi.o \
lttng-context-vtid.o lttng-context-ppid.o \
lttng-context-vppid.o lttng-calibrate.o \
lttng-context-hostname.o wrapper/random.o \
- probes/lttng.o
+ probes/lttng.o wrapper/trace-clock.o
obj-m += lttng-statedump.o
lttng-statedump-objs := lttng-statedump-impl.o wrapper/irqdesc.o \
diff --git a/wrapper/trace-clock.c b/wrapper/trace-clock.c
new file mode 100644
index 0000000..ac44084
--- /dev/null
+++ b/wrapper/trace-clock.c
@@ -0,0 +1,29 @@
+/*
+ * wrapper/trace-clock.c
+ *
+ * Contains LTTng trace clock mapping to LTTng trace clock or mainline monotonic
+ * clock. This wrapper depends on CONFIG_HIGH_RES_TIMERS=y.
+ *
+ * Copyright (C) 2011-2012 Mathieu Desnoyers <mathieu.desnoyers at efficios.com>
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; only
+ * version 2.1 of the License.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+#include "trace-clock.h"
+
+#if (LINUX_VERSION_CODE >= KERNEL_VERSION(3,16,0))
+DEFINE_PER_CPU(local_t, lttng_last_tsc);
+EXPORT_PER_CPU_SYMBOL(lttng_last_tsc);
+#endif /* #else #if (LINUX_VERSION_CODE >= KERNEL_VERSION(3,16,0)) */
diff --git a/wrapper/trace-clock.h b/wrapper/trace-clock.h
index 9c0c806..68df48d 100644
--- a/wrapper/trace-clock.h
+++ b/wrapper/trace-clock.h
@@ -32,7 +32,9 @@
#include <linux/ktime.h>
#include <linux/time.h>
#include <linux/hrtimer.h>
+#include <linux/percpu.h>
#include <linux/version.h>
+#include <asm/local.h>
#include "../lttng-kernel-version.h"
#include "random.h"
@@ -40,6 +42,88 @@
#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."
#endif
+#if (LINUX_VERSION_CODE >= KERNEL_VERSION(3,16,0))
+
+DECLARE_PER_CPU(local_t, lttng_last_tsc);
+
+#if (BITS_PER_LONG == 32)
+/*
+ * Fixup "src_now" using the 32 LSB from "last". We need to handle overflow and
+ * underflow of the 32nd bit. "last" can be above, below or equal to the 32 LSB
+ * of "src_now".
+ */
+static inline u64 trace_clock_fixup(u64 src_now, u32 last)
+{
+ u64 now;
+
+ now = src_now & 0xFFFFFFFF00000000ULL;
+ now |= (u64) last;
+ /* Detect overflow or underflow between now and last. */
+ if ((src_now & 0x80000000U) && !(last & 0x80000000U)) {
+ /*
+ * If 32nd bit transitions from 1 to 0, and we move forward in
+ * time from "now" to "last", then we have an overflow.
+ */
+ if (((s32) now - (s32) last) < 0)
+ now += 0x0000000100000000ULL;
+ } else if (!(src_now & 0x80000000U) && (last & 0x80000000U)) {
+ /*
+ * If 32nd bit transitions from 0 to 1, and we move backward in
+ * time from "now" to "last", then we have an underflow.
+ */
+ if (((s32) now - (s32) last) > 0)
+ now -= 0x0000000100000000ULL;
+ }
+ return now;
+}
+#else /* #if (BITS_PER_LONG == 32) */
+/*
+ * The fixup is pretty easy on 64-bit architectures: "last" is a 64-bit
+ * value, so we can use last directly as current time.
+ */
+static inline u64 trace_clock_fixup(u64 src_now, unsigned long last)
+{
+ return (u64) last;
+}
+#endif /* #else #if (BITS_PER_LONG == 32) */
+
+/*
+ * Always called with preemption disabled. Can be interrupted.
+ */
+static inline u64 trace_clock_monotonic_wrapper(void)
+{
+ u64 now;
+ unsigned long last, result;
+ local_t *last_tsc;
+
+ /* Use fast nmi-safe monotonic clock provided by the Linux kernel. */
+ last_tsc = &__get_cpu_var(lttng_last_tsc);
+ last = local_read(last_tsc);
+ /*
+ * 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 (((long) now - (long) last) < 0)
+ now = trace_clock_fixup(now, last);
+ result = local_cmpxchg(last_tsc, last, (unsigned long) now);
+ 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 trace_clock_fixup(now, result);
+ }
+}
+
+#else /* #if (LINUX_VERSION_CODE >= KERNEL_VERSION(3,16,0)) */
static inline u64 trace_clock_monotonic_wrapper(void)
{
ktime_t ktime;
@@ -54,6 +138,7 @@ static inline u64 trace_clock_monotonic_wrapper(void)
ktime = ktime_get();
return ktime_to_ns(ktime);
}
+#endif /* #else #if (LINUX_VERSION_CODE >= KERNEL_VERSION(3,16,0)) */
static inline u32 trace_clock_read32(void)
{
@@ -75,23 +160,19 @@ static inline int trace_clock_uuid(char *uuid)
return wrapper_get_bootid(uuid);
}
+#if (LINUX_VERSION_CODE >= KERNEL_VERSION(3,16,0))
static inline int get_trace_clock(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");
-
+ printk(KERN_WARNING "LTTng: Using mainline kernel monotonic fast clock, which is NMI-safe.\n");
+ return 0;
+}
+#else /* #if (LINUX_VERSION_CODE >= KERNEL_VERSION(3,16,0)) */
+static inline int get_trace_clock(void)
+{
+ printk(KERN_WARNING "LTTng: Using mainline kernel monotonic clock. NMIs will not be traced.\n");
return 0;
}
+#endif /* #else #if (LINUX_VERSION_CODE >= KERNEL_VERSION(3,16,0)) */
static inline void put_trace_clock(void)
{
--
1.7.10.4
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