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Date:      Mon, 16 Sep 2019 06:15:23 +0000 (UTC)
From:      Konstantin Belousov <kib@FreeBSD.org>
To:        src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-stable@freebsd.org, svn-src-stable-12@freebsd.org
Subject:   svn commit: r352380 - stable/12/sys/kern
Message-ID:  <201909160615.x8G6FN1U096263@repo.freebsd.org>
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Author: kib
Date: Mon Sep 16 06:15:22 2019
New Revision: 352380
URL: https://svnweb.freebsd.org/changeset/base/352380

Log:
  MFC r352059, r352060:
  Make timehands count selectable at boottime.

Modified:
  stable/12/sys/kern/kern_tc.c
Directory Properties:
  stable/12/   (props changed)

Modified: stable/12/sys/kern/kern_tc.c
==============================================================================
--- stable/12/sys/kern/kern_tc.c	Mon Sep 16 06:13:29 2019	(r352379)
+++ stable/12/sys/kern/kern_tc.c	Mon Sep 16 06:15:22 2019	(r352380)
@@ -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 +112,11 @@ 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 | CTLFLAG_NOFETCH,
+    &timehands_count, 0, "Count of timehands in rotation");
+
 struct bintime bt_timethreshold;
 struct bintime bt_tickthreshold;
 sbintime_t sbt_timethreshold;
@@ -1956,7 +1958,26 @@ done:
 	return (0);
 }
 
+/* Set up the requested number of timehands. */
 static void
+inittimehands(void *dummy)
+{
+	struct timehands *thp;
+	int i;
+
+	TUNABLE_INT_FETCH("kern.timecounter.timehands_count",
+	    &timehands_count);
+	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];
+}
+SYSINIT(timehands, SI_SUB_TUNABLES, SI_ORDER_ANY, inittimehands, NULL);
+
+static void
 inittimecounter(void *dummy)
 {
 	u_int p;
@@ -1986,6 +2007,7 @@ inittimecounter(void *dummy)
 #ifdef FFCLOCK
 	ffclock_init();
 #endif
+
 	/* warm up new timecounter (again) and get rolling. */
 	(void)timecounter->tc_get_timecount(timecounter);
 	(void)timecounter->tc_get_timecount(timecounter);

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