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Date:      Sun, 11 Jul 2010 16:47:46 +0000 (UTC)
From:      Alexander Motin <mav@FreeBSD.org>
To:        src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org
Subject:   svn commit: r209900 - head/sys/kern
Message-ID:  <201007111647.o6BGlk0O033551@svn.freebsd.org>
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Author: mav
Date: Sun Jul 11 16:47:45 2010
New Revision: 209900
URL: http://svn.freebsd.org/changeset/base/209900

Log:
  Remove interval validation from cpu_tick_calibrate(). As I found, check
  was needed at preliminary version of the patch, where number of CPU ticks
  was divided strictly on 16 seconds. Final code instead uses real interval
  duration, so precise interval should not be important. Same time aliasing
  issues around second boundary causes false positives, periodically logging
  useless "t_delta ... too long/short" messages when HZ set below 256.

Modified:
  head/sys/kern/kern_tc.c

Modified: head/sys/kern/kern_tc.c
==============================================================================
--- head/sys/kern/kern_tc.c	Sun Jul 11 15:32:20 2010	(r209899)
+++ head/sys/kern/kern_tc.c	Sun Jul 11 16:47:45 2010	(r209900)
@@ -864,43 +864,21 @@ cpu_tick_calibrate(int reset)
 		t_delta = t_this;
 		bintime_sub(&t_delta, &t_last);
 		/*
-		 * Validate that 16 +/- 1/256 seconds passed. 
-		 * After division by 16 this gives us a precision of
-		 * roughly 250PPM which is sufficient
+		 * Headroom:
+		 * 	2^(64-20) / 16[s] =
+		 * 	2^(44) / 16[s] =
+		 * 	17.592.186.044.416 / 16 =
+		 * 	1.099.511.627.776 [Hz]
 		 */
-		if (t_delta.sec > 16 || (
-		    t_delta.sec == 16 && t_delta.frac >= (0x01LL << 56))) {
-			/* too long */
-			if (bootverbose)
-				printf("t_delta %ju.%016jx too long\n",
-				    (uintmax_t)t_delta.sec,
-				    (uintmax_t)t_delta.frac);
-		} else if (t_delta.sec < 15 ||
-		    (t_delta.sec == 15 && t_delta.frac <= (0xffLL << 56))) {
-			/* too short */
-			if (bootverbose)
-				printf("t_delta %ju.%016jx too short\n",
-				    (uintmax_t)t_delta.sec,
-				    (uintmax_t)t_delta.frac);
-		} else {
-			/* just right */
-			/*
-			 * Headroom:
-			 * 	2^(64-20) / 16[s] =
-			 * 	2^(44) / 16[s] =
-			 * 	17.592.186.044.416 / 16 =
-			 * 	1.099.511.627.776 [Hz]
-			 */
-			divi = t_delta.sec << 20;
-			divi |= t_delta.frac >> (64 - 20);
-			c_delta <<= 20;
-			c_delta /= divi;
-			if (c_delta  > cpu_tick_frequency) {
-				if (0 && bootverbose)
-					printf("cpu_tick increased to %ju Hz\n",
-					    c_delta);
-				cpu_tick_frequency = c_delta;
-			}
+		divi = t_delta.sec << 20;
+		divi |= t_delta.frac >> (64 - 20);
+		c_delta <<= 20;
+		c_delta /= divi;
+		if (c_delta > cpu_tick_frequency) {
+			if (0 && bootverbose)
+				printf("cpu_tick increased to %ju Hz\n",
+				    c_delta);
+			cpu_tick_frequency = c_delta;
 		}
 	}
 	c_last = c_this;

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