Module Name: src
Committed By: jruoho
Date: Wed Nov 20 18:13:16 UTC 2013
Modified Files:
src/share/man/man9/man9.x86: tsc.9
Log Message:
Don't be so pessimistic.
To generate a diff of this commit:
cvs rdiff -u -r1.4 -r1.5 src/share/man/man9/man9.x86/tsc.9
Please note that diffs are not public domain; they are subject to the
copyright notices on the relevant files.
Modified files:
Index: src/share/man/man9/man9.x86/tsc.9
diff -u src/share/man/man9/man9.x86/tsc.9:1.4 src/share/man/man9/man9.x86/tsc.9:1.5
--- src/share/man/man9/man9.x86/tsc.9:1.4 Tue Oct 25 05:41:35 2011
+++ src/share/man/man9/man9.x86/tsc.9 Wed Nov 20 18:13:16 2013
@@ -1,4 +1,4 @@
-.\" $NetBSD: tsc.9,v 1.4 2011/10/25 05:41:35 jruoho Exp $
+.\" $NetBSD: tsc.9,v 1.5 2013/11/20 18:13:16 jruoho Exp $
.\"
.\" Copyright (c) 2011 The NetBSD Foundation, Inc.
.\" All rights reserved.
@@ -27,7 +27,7 @@
.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
.\" POSSIBILITY OF SUCH DAMAGE.
.\"
-.Dd October 25, 2011
+.Dd November 20, 2013
.Dt TSC 9 x86
.Os
.Sh NAME
@@ -59,32 +59,25 @@ register has been present since the orig
.Pp
Already because of the access method,
.Tn TSC
-has traditionally provided a low-overhead and high-resolution
+provides a low-overhead and high-resolution
way to obtain
.Tn CPU
timing information.
-Recently, however, this reliability has been undermined by
-such factors as system sleep states,
+This traditional premise was violated when such factors as
+system sleep states,
.Tn CPU
.Dq hotplugging ,
.Dq hibernation ,
and
.Tn CPU
-frequency scaling.
-.Pp
-These potential new sources of unreliability are easily understandable
-when one recalls that the counter measures cycles and not
-.Dq time .
-Comparing the cycle counts only makes sense when the clock frequency
-is stable; to convert the cycle counts to time units, a general equation
-would be:
-.Dq seconds = cycles / frequency in Hz .
-The use of
-.Tn TSC
-as a source of high-resolution timing can be thus discouraged.
-But the basic premise is still guaranteed:
-.Tn TSC
-is a monotonically increasing counter.
+frequency scaling
+were introduced to the x86 lineage.
+This was however mainly a short abruption:
+in many new x86
+.Tn CPUs
+the time stamp counter is again invariant with
+respect to the stability of the clock frequency.
+Care should be however taken in implementations that rely on this assumption.
.Sh FUNCTIONS
.Bl -tag -width abcd
.It Fn rdtsc ""
