Add a consistent API to a feature that most modern CPUs have; a fast

counter register in-CPU.

This is to be used as a fast "timer", where linearity is more important
than time, and multiple lines in the linearity caused by multiple CPUs
in an SMP machine is not a problem.

This adds no code whatsoever to the FreeBSD kernel until it is actually
used, and then as a single-instruction inline routine (except for the
80386 and 80486 where it is some more inline code around nanotime(9).

Reviewed by:	bde, kris, jhb

1 files changed, 10 insertions, 0 deletions

diff --git a/sys/alpha/include/cpu.h b/sys/alpha/include/cpu.h
index a45b4d1..a0be38f 100644
--- a/sys/alpha/include/cpu.h
+++ b/sys/alpha/include/cpu.h
@@ -173,6 +173,16 @@ void	syscall __P((u_int64_t, struct trapframe *));
 void	trap __P((unsigned long, unsigned long, unsigned long, unsigned long,
 	    struct trapframe *));
 
+/*
+ * Return contents of in-cpu fast counter as a sort of "bogo-time"
+ * for non-critical timing.
+ */
+static __inline u_int64_t
+get_cyclecount(void)
+{
+	return (alpha_rpcc());
+}
+
 #endif /* _KERNEL */
 
 #endif /* _ALPHA_CPU_H_ */