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From: John Birrell <jb@FreeBSD.org>
To: Perforce Change Reviews <perforce@freebsd.org>
Cc: 
Subject: PERFORCE change 98707 for review
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http://perforce.freebsd.org/chv.cgi?CH=98707

Change 98707 by jb@jb_freebsd2 on 2006/06/06 23:29:58

	Add a function for DTrace to get the uptime in it's high
	resolution format (nanoseconds) without calling any other
	functions (which would violate the probe context call
	rules).
	
	Note that this only works on Pentium processors and above
	where the TSC is being used. It doesn't address any issues
	with TSC differences between processors. So there is more
	work required here.
	
	rdtsc() is an inline function so it doesn't violate the
	probe context rules.

Affected files ...

.. //depot/projects/dtrace/src/sys/i386/i386/tsc.c#2 edit

Differences ...

==== //depot/projects/dtrace/src/sys/i386/i386/tsc.c#2 (text+ko) ====

@@ -28,6 +28,7 @@
 __FBSDID("$FreeBSD: src/sys/i386/i386/tsc.c,v 1.205 2006/02/11 09:33:06 phk Exp $");
 
 #include "opt_clock.h"
+#include "opt_kdtrace.h"
 
 #include <sys/param.h>
 #include <sys/systm.h>
@@ -153,3 +154,18 @@
 {
 	return (rdtsc());
 }
+
+/*
+ * DTrace needs a high resolution time function which can
+ * be called from a probe context and guaranteed not to have
+ * instrumented with probes itself.
+ *
+ * Returns nanoseconds since boot.
+ */
+#ifdef KDTRACE
+uint64_t
+dtrace_gethrtime()
+{
+	return (rdtsc() * (uint64_t) 1000000000 / tsc_freq);
+}
+#endif