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Date:      Mon, 9 Sep 2019 11:29:59 +0000 (UTC)
From:      Konstantin Belousov <kib@FreeBSD.org>
To:        src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org
Subject:   svn commit: r352059 - head/sys/kern
Message-ID:  <201909091129.x89BTxvw061871@repo.freebsd.org>
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Author: kib
Date: Mon Sep  9 11:29:58 2019
New Revision: 352059
URL: https://svnweb.freebsd.org/changeset/base/352059

Log:
  Make timehands count selectable at boottime.
  
  Tested by:	O'Connor, Daniel <darius@dons.net.au>
  Sponsored by:	The FreeBSD Foundation
  MFC after:	1 week
  Differential revision:	https://reviews.freebsd.org/D21563

Modified:
  head/sys/kern/kern_tc.c

Modified: head/sys/kern/kern_tc.c
==============================================================================
--- head/sys/kern/kern_tc.c	Mon Sep  9 11:22:38 2019	(r352058)
+++ head/sys/kern/kern_tc.c	Mon Sep  9 11:29:58 2019	(r352059)
@@ -83,19 +83,16 @@ struct timehands {
 	struct timehands	*th_next;
 };
 
-static struct timehands th0;
-static struct timehands th1 = {
-	.th_next = &th0
-};
-static struct timehands th0 = {
+static struct timehands ths[16] = {
+    [0] =  {
 	.th_counter = &dummy_timecounter,
 	.th_scale = (uint64_t)-1 / 1000000,
 	.th_offset = { .sec = 1 },
 	.th_generation = 1,
-	.th_next = &th1
+    },
 };
 
-static struct timehands *volatile timehands = &th0;
+static struct timehands *volatile timehands = &ths[0];
 struct timecounter *timecounter = &dummy_timecounter;
 static struct timecounter *timecounters = &dummy_timecounter;
 
@@ -115,6 +112,10 @@ static int timestepwarnings;
 SYSCTL_INT(_kern_timecounter, OID_AUTO, stepwarnings, CTLFLAG_RW,
     &timestepwarnings, 0, "Log time steps");
 
+static int timehands_count = 2;
+SYSCTL_INT(_kern_timecounter, OID_AUTO, timehands_count, CTLFLAG_RDTUN,
+    &timehands_count, 0, "Count of timehands in rotation");
+
 struct bintime bt_timethreshold;
 struct bintime bt_tickthreshold;
 sbintime_t sbt_timethreshold;
@@ -1960,8 +1961,9 @@ done:
 static void
 inittimecounter(void *dummy)
 {
+	struct timehands *thp;
 	u_int p;
-	int tick_rate;
+	int i, tick_rate;
 
 	/*
 	 * Set the initial timeout to
@@ -1987,6 +1989,16 @@ inittimecounter(void *dummy)
 #ifdef FFCLOCK
 	ffclock_init();
 #endif
+
+	/* Set up the requested number of timehands. */
+	if (timehands_count < 1)
+		timehands_count = 1;
+	if (timehands_count > nitems(ths))
+		timehands_count = nitems(ths);
+	for (i = 1, thp = &ths[0]; i < timehands_count;  thp = &ths[i++])
+		thp->th_next = &ths[i];
+	thp->th_next = &ths[0];
+
 	/* warm up new timecounter (again) and get rolling. */
 	(void)timecounter->tc_get_timecount(timecounter);
 	(void)timecounter->tc_get_timecount(timecounter);

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