git: 6b82130e6c9a - main - clock: Add a long ticks variable, ticksl

The branch main has been updated by markj:

URL: https://cgit.FreeBSD.org/src/commit/?id=6b82130e6c9add4a8892ca897df5a0ec04663ea2

commit 6b82130e6c9add4a8892ca897df5a0ec04663ea2
Author:     Mark Johnston <markj@FreeBSD.org>
AuthorDate: 2025-01-10 15:37:07 +0000
Commit:     Mark Johnston <markj@FreeBSD.org>
CommitDate: 2025-01-10 15:42:59 +0000

    clock: Add a long ticks variable, ticksl
    
    For compatibility with Linux, it's useful to have a tick counter of
    width sizeof(long), but our tick counter is an int.  Currently the
    linuxkpi tries paper over this difference, but this cannot really be
    done reliably, so it's desirable to have a wider tick counter.  This
    change introduces ticksl, keeping the existing ticks variable.
    
    Follow a suggestion from kib to avoid having to maintain two separate
    counters and to avoid converting existing code to use ticksl: change
    hardclock() to update ticksl instead of ticks, and then use assembler
    directives to make ticks and ticksl overlap such that loading ticks
    gives the bottom 32 bits.  This makes it possible to use ticksl in the
    linuxkpi without having to convert any native code, and without making
    hardclock() more complicated or expensive.  Then, the linuxkpi can be
    modified to use ticksl instead of ticks.
    
    Reviewed by:    olce, kib, emaste
    MFC after:      1 month
    Differential Revision:  https://reviews.freebsd.org/D48383
---
 sys/conf/files        |  1 +
 sys/kern/kern_clock.c | 26 ++++++++++++++------------
 sys/kern/kern_tc.c    |  4 ++--
 sys/kern/subr_param.c |  2 +-
 sys/kern/subr_ticks.s | 44 ++++++++++++++++++++++++++++++++++++++++++++
 sys/sys/kernel.h      |  9 +++++++++
 sys/sys/timetc.h      |  2 +-
 7 files changed, 72 insertions(+), 16 deletions(-)

diff --git a/sys/conf/files b/sys/conf/files
index d358737c5613..a630d9dd72bc 100644
--- a/sys/conf/files
+++ b/sys/conf/files
@@ -3932,6 +3932,7 @@ kern/subr_stack.c		optional ddb | stack | ktr
 kern/subr_stats.c		optional stats
 kern/subr_taskqueue.c		standard
 kern/subr_terminal.c		optional vt
+kern/subr_ticks.s		standard
 kern/subr_trap.c		standard
 kern/subr_turnstile.c		standard
 kern/subr_uio.c			standard
diff --git a/sys/kern/kern_clock.c b/sys/kern/kern_clock.c
index 6fa2272ed54a..b11c0d235139 100644
--- a/sys/kern/kern_clock.c
+++ b/sys/kern/kern_clock.c
@@ -323,7 +323,7 @@ read_cpu_time(long *cp_time)
 
 #include <sys/watchdog.h>
 
-static int watchdog_ticks;
+static long watchdog_ticks;
 static int watchdog_enabled;
 static void watchdog_fire(void);
 static void watchdog_config(void *, u_int, int *);
@@ -369,10 +369,9 @@ watchdog_attach(void)
 int	stathz;
 int	profhz;
 int	profprocs;
-volatile int	ticks;
 int	psratio;
 
-DPCPU_DEFINE_STATIC(int, pcputicks);	/* Per-CPU version of ticks. */
+DPCPU_DEFINE_STATIC(long, pcputicks);	/* Per-CPU version of ticks. */
 #ifdef DEVICE_POLLING
 static int devpoll_run = 0;
 #endif
@@ -480,14 +479,14 @@ hardclock(int cnt, int usermode)
 	struct pstats *pstats;
 	struct thread *td = curthread;
 	struct proc *p = td->td_proc;
-	int *t = DPCPU_PTR(pcputicks);
-	int global, i, newticks;
+	long global, newticks, *t;
 
 	/*
 	 * Update per-CPU and possibly global ticks values.
 	 */
+	t = DPCPU_PTR(pcputicks);
 	*t += cnt;
-	global = ticks;
+	global = atomic_load_long(&ticksl);
 	do {
 		newticks = *t - global;
 		if (newticks <= 0) {
@@ -496,7 +495,7 @@ hardclock(int cnt, int usermode)
 			newticks = 0;
 			break;
 		}
-	} while (!atomic_fcmpset_int(&ticks, &global, *t));
+	} while (!atomic_fcmpset_long(&ticksl, &global, *t));
 
 	/*
 	 * Run current process's virtual and profile time, as needed.
@@ -525,8 +524,10 @@ hardclock(int cnt, int usermode)
 		}
 #endif /* DEVICE_POLLING */
 		if (watchdog_enabled > 0) {
-			i = atomic_fetchadd_int(&watchdog_ticks, -newticks);
-			if (i > 0 && i <= newticks)
+			long left;
+
+			left = atomic_fetchadd_long(&watchdog_ticks, -newticks);
+			if (left > 0 && left <= newticks)
 				watchdog_fire();
 		}
 		intr_event_handle(clk_intr_event, NULL);
@@ -540,11 +541,12 @@ hardclock(int cnt, int usermode)
 void
 hardclock_sync(int cpu)
 {
-	int *t;
+	long *t;
+
 	KASSERT(!CPU_ABSENT(cpu), ("Absent CPU %d", cpu));
-	t = DPCPU_ID_PTR(cpu, pcputicks);
 
-	*t = ticks;
+	t = DPCPU_ID_PTR(cpu, pcputicks);
+	*t = ticksl;
 }
 
 /*
diff --git a/sys/kern/kern_tc.c b/sys/kern/kern_tc.c
index 26f09cb60260..a797a101bf6f 100644
--- a/sys/kern/kern_tc.c
+++ b/sys/kern/kern_tc.c
@@ -1916,9 +1916,9 @@ SYSCTL_INT(_kern_timecounter, OID_AUTO, tick, CTLFLAG_RD, &tc_tick, 0,
     "Approximate number of hardclock ticks in a millisecond");
 
 void
-tc_ticktock(int cnt)
+tc_ticktock(long cnt)
 {
-	static int count;
+	static long count;
 
 	if (mtx_trylock_spin(&tc_setclock_mtx)) {
 		count += cnt;
diff --git a/sys/kern/subr_param.c b/sys/kern/subr_param.c
index 19169ba63061..f4359efec466 100644
--- a/sys/kern/subr_param.c
+++ b/sys/kern/subr_param.c
@@ -197,7 +197,7 @@ init_param1(void)
 	 * Arrange for ticks to wrap 10 minutes after boot to help catch
 	 * sign problems sooner.
 	 */
-	ticks = INT_MAX - (hz * 10 * 60);
+	ticksl = INT_MAX - (hz * 10 * 60);
 
 	vn_lock_pair_pause_max = hz / 100;
 	if (vn_lock_pair_pause_max == 0)
diff --git a/sys/kern/subr_ticks.s b/sys/kern/subr_ticks.s
new file mode 100644
index 000000000000..6565ba424137
--- /dev/null
+++ b/sys/kern/subr_ticks.s
@@ -0,0 +1,44 @@
+/*-
+ * SPDX-License-Identifier: BSD-2-Clause
+ *
+ * Copyright (c) 2025 Mark Johnston <markj@FreeBSD.org>
+ */
+
+/*
+ * Define the "ticks" and "ticksl" variables.  The former is overlaid onto the
+ * low bits of the latter.
+ */
+
+#if defined(__aarch64__)
+#include <sys/elf_common.h>
+#include <machine/asm.h>
+
+GNU_PROPERTY_AARCH64_FEATURE_1_NOTE(GNU_PROPERTY_AARCH64_FEATURE_1_VAL)
+#endif
+
+#ifdef _ILP32
+#define	SIZEOF_TICKSL	4
+#define	TICKSL_INIT	.long 0
+#else
+#define	SIZEOF_TICKSL	8
+#define	TICKSL_INIT	.quad 0
+#endif
+
+#if defined(_ILP32) || __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
+#define	TICKS_OFFSET	0
+#else
+#define	TICKS_OFFSET	4
+#endif
+
+	.data
+
+	.global ticksl
+	.type ticksl, %object
+	.align SIZEOF_TICKSL
+ticksl:	TICKSL_INIT
+	.size ticksl, SIZEOF_TICKSL
+
+	.global ticks
+	.type ticks, %object
+ticks	=ticksl + TICKS_OFFSET
+	.size ticks, 4
diff --git a/sys/sys/kernel.h b/sys/sys/kernel.h
index 3144b5a50c98..380099092107 100644
--- a/sys/sys/kernel.h
+++ b/sys/sys/kernel.h
@@ -65,7 +65,16 @@ extern int psratio;			/* ratio: prof / stat */
 extern int stathz;			/* statistics clock's frequency */
 extern int profhz;			/* profiling clock's frequency */
 extern int profprocs;			/* number of process's profiling */
+
+/*
+ * The ticks and ticksl symbols overlap, giving a 64-bit tick counter on 64-bit
+ * platforms while still maintaining compatibility with the legacy 32-bit
+ * counter.  Either value can be used, but rollover must be handled; at 1000Hz,
+ * ticks (and ticksl on 32-bit platforms) roll over roughly every 25 days.  On
+ * 64-bit platforms, ticksl will not roll over in the foreseeable future.
+ */
 extern volatile int ticks;
+extern volatile long ticksl;
 
 #endif /* _KERNEL */
 
diff --git a/sys/sys/timetc.h b/sys/sys/timetc.h
index 1d9b18620e96..522770868425 100644
--- a/sys/sys/timetc.h
+++ b/sys/sys/timetc.h
@@ -87,7 +87,7 @@ extern int tc_min_ticktock_freq; /*
 u_int64_t tc_getfrequency(void);
 void	tc_init(struct timecounter *tc);
 void	tc_setclock(struct timespec *ts);
-void	tc_ticktock(int cnt);
+void	tc_ticktock(long cnt);
 void	cpu_tick_calibration(void);
 
 #ifdef SYSCTL_DECL