From: Jim Houston <jim.houston@attbi.com>
To: linux-kernel@vger.kernel.org,
high-res-timers-discourse@lists.sourceforge.net,
jim.houston@ccur.com
Subject: [PATCH] calibrate_tsc should not use HZ
Date: Thu, 31 Oct 2002 14:28:50 -0500 [thread overview]
Message-ID: <200210311928.g9VJSoY03708@linux.local> (raw)
Hi Everyone,
I noticed that the calibration time for calibrate_tsc() is 5 jiffies.
This means the result with 1000 Hz jiffies may be less accurate
then it was at 100 Hz. The attached patch removes this dependency.
Jim Houston - Concurrent Computer Corp.
diff -X /usr1/jhouston/dontdiff -ur linux.orig/arch/i386/kernel/timers/timer_tsc.c linux.kdb/arch/i386/kernel/timers/timer_tsc.c
--- linux.orig/arch/i386/kernel/timers/timer_tsc.c Wed Oct 23 00:54:19 2002
+++ linux.kdb/arch/i386/kernel/timers/timer_tsc.c Thu Oct 31 14:18:21 2002
@@ -97,8 +97,13 @@
* device.
*/
-#define CALIBRATE_LATCH (5 * LATCH)
-#define CALIBRATE_TIME (5 * 1000020/HZ)
+/*
+ * Pick the largest possible latch value (it is a 16 bit counter)
+ * and calculate the corresponding time.
+ */
+#define CALIBRATE_LATCH (0xffff)
+#define CALIBRATE_TIME ((int)((1000000LL*CALIBRATE_LATCH + \
+ CLOCK_TICK_RATE/2)/CLOCK_TICK_RATE)
static unsigned long __init calibrate_tsc(void)
{
next reply other threads:[~2002-10-31 19:22 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2002-10-31 19:28 Jim Houston [this message]
2002-10-31 19:52 ` [PATCH] calibrate_tsc should not use HZ george anzinger
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