X-Git-Url: https://git.lttng.org/?a=blobdiff_plain;f=share%2Fkernelcompat.h;h=5cc5eaa22e70b963795619b963c1c2f8ed9504da;hb=93d0f2eaff675059588e958e3de74a1bb7dd4028;hp=2a8e0f253d1158e637d53f130eea3ca49de8b241;hpb=08230db7e2e536bddf0015fa663b6d10abea30f1;p=ust.git

diff --git a/share/kernelcompat.h b/share/kernelcompat.h
index 2a8e0f2..5cc5eaa 100644
--- a/share/kernelcompat.h
+++ b/share/kernelcompat.h
@@ -1,7 +1,6 @@
 #ifndef KERNELCOMPAT_H
 #define KERNELCOMPAT_H
 
-#include <compiler.h>
 #include <kcompat.h>
 
 #include <string.h>
@@ -150,6 +149,23 @@ static __inline__ int get_count_order(unsigned int count)
 
 /* TRACE CLOCK */
 
+/* There are two types of clocks that can be used.
+   - TSC based clock
+   - gettimeofday() clock
+
+   Microbenchmarks on Linux 2.6.30 on Core2 Duo 3GHz (functions are inlined):
+     Calls (100000000) to tsc(): 4004035641 cycles or 40 cycles/call
+     Calls (100000000) to gettimeofday(): 9723158352 cycles or 97 cycles/call
+
+   For merging traces with the kernel, a time source compatible with that of
+   the kernel is necessary.
+
+*/
+
+#if 0
+/* WARNING: Make sure to set frequency and scaling functions that will not
+ * result in lttv timestamps (sec.nsec) with seconds greater than 2**32-1.
+ */
 static inline u64 trace_clock_read64(void)
 {
 	uint32_t low;
@@ -161,8 +177,8 @@ static inline u64 trace_clock_read64(void)
 	retval <<= 32;
 	return retval | low;
 }
+#endif
 
-#if 0
 static inline u64 trace_clock_read64(void)
 {
 	struct timeval tv;
@@ -175,7 +191,6 @@ static inline u64 trace_clock_read64(void)
 
 	return retval;
 }
-#endif
 
 static inline u64 trace_clock_frequency(void)
 {