X-Git-Url: http://git.lttng.org/?p=lttng-modules.git;a=blobdiff_plain;f=wrapper%2Ftrace-clock.h;h=b145b826571ee4fe3095973a0f6360de3344c9e6;hp=9c0c8067f7b1d959af34c47f396e71e4496d334c;hb=b07252070edd244987bf160c1ee488d4796bb3a3;hpb=c340f0713c0e9eb2c7aaae21bf2b03e7e19aca6d

diff --git a/wrapper/trace-clock.h b/wrapper/trace-clock.h
index 9c0c8067..b145b826 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(3,17,0))
+
+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, u64 last)
+{
+	return 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(3,17,0)) */
 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(3,17,0)) */
 
 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(3,17,0))
 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(3,17,0)) */
+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(3,17,0)) */
 
 static inline void put_trace_clock(void)
 {