Use 3.17 ktime_get_mono_fast_ns() new API

[lttng-modules.git] / wrapper / trace-clock.h

diff --git a/wrapper/trace-clock.h b/wrapper/trace-clock.h
index 9c0c8067f7b1d959af34c47f396e71e4496d334c..b145b826571ee4fe3095973a0f6360de3344c9e6 100644 (file)
--- 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)
 {