From owner-freebsd-arch  Thu Nov 16 22:55:26 2000
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To: arch@freebsd.org
Subject: new monotime() call for all architectures.
Date: Fri, 17 Nov 2000 08:55:04 +0200
From: Mark Murray <mark@grondar.za>
Sender: owner-freebsd-arch@FreeBSD.ORG
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Hi all

I need a fast-as-possible "time" inside the kernel to help
speed up the /dev/random device. I say "time", because although
it needs to be a function of time (preferably accurate and linear),
it has no need whatsoever to be "real time", so a simple counter
is quite OK.

Pentiums, Alphas and IA64's all have a suitable register on chip,
while I have to make do with nanotime(9) on i386 and i486.

I have prepared a monotime(9) call for the i386, alpha and ia64
architectures (patch enclosed). I have been running this for a
week or two now with promising results (on a Pentium). With
the exception of the minimum of "glue" (and nanotime on older
architectures), these functions reduce to one instruction.

Comments? Suggestions? Nobel Prize nominations? I'd like to
commit this soonish if possible.

M

Index: alpha/include/clock.h
===================================================================
RCS file: /home/ncvs/src/sys/alpha/include/clock.h,v
retrieving revision 1.6
diff -u -d -r1.6 clock.h
--- alpha/include/clock.h	2000/10/15 09:51:44	1.6
+++ alpha/include/clock.h	2000/11/08 06:02:24
@@ -19,6 +19,18 @@
 int	acquire_timer2 __P((int mode));
 int	release_timer2 __P((void));
 
+/*
+ * Standardised monotonic counter interface
+ */
+static __inline u_int64_t
+monotime(void)
+{
+	u_int64_t retval;
+
+	__asm__ __volatile__ ("rpcc %0" : "=r" (retval));
+	return retval;
+}
+
 #endif
 
 #endif /* !_MACHINE_CLOCK_H_ */
Index: i386/include/clock.h
===================================================================
RCS file: /home/ncvs/src/sys/i386/include/clock.h,v
retrieving revision 1.39
diff -u -d -r1.39 clock.h
--- i386/include/clock.h	2000/10/15 09:51:48	1.39
+++ i386/include/clock.h	2000/11/08 06:47:24
@@ -45,6 +45,23 @@
 int	sysbeep __P((int pitch, int period));
 void	i8254_restore __P((void));
 
+/*
+ * Standardised monotonic counter interface
+ */
+static __inline u_int64_t
+monotime(void)
+{
+	u_int64_t retval;
+
+#if defined(I386_CPU) || defined(I486_CPU)
+	if (!tsc_present)
+		retval = nanotime();
+	else
+#endif
+		__asm __volatile("rdtsc" : "=A" (retval));
+	return retval;
+}
+
 #endif /* _KERNEL */
 
 #endif /* !_MACHINE_CLOCK_H_ */
Index: ia64/include/clock.h
===================================================================
RCS file: /home/ncvs/src/sys/ia64/include/clock.h,v
retrieving revision 1.2
diff -u -d -r1.2 clock.h
--- ia64/include/clock.h	2000/10/15 09:51:48	1.2
+++ ia64/include/clock.h	2000/11/08 06:02:47
@@ -19,6 +19,18 @@
 int	acquire_timer2 __P((int mode));
 int	release_timer2 __P((void));
 
+/*
+ * Standardised monotonic counter interface
+ */
+static __inline u_int64_t
+monotime(void)
+{
+	u_int64_t retval;
+
+	__asm __volatile("mov %0=ar.itc" : "=r" (retval));
+	return retval;
+}
+
 #endif
 
 #endif /* !_MACHINE_CLOCK_H_ */


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