git: 467fa302c3ae - stable/14 - clock: Add a long ticks variable, ticksl
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Date: Fri, 14 Feb 2025 19:25:29 UTC
The branch stable/14 has been updated by markj:
URL: https://cgit.FreeBSD.org/src/commit/?id=467fa302c3aeefd7ccd9fa6bd0ad0381d86cd75b
commit 467fa302c3aeefd7ccd9fa6bd0ad0381d86cd75b
Author: Mark Johnston <markj@FreeBSD.org>
AuthorDate: 2025-01-10 15:37:07 +0000
Commit: Mark Johnston <markj@FreeBSD.org>
CommitDate: 2025-02-14 19:25:18 +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
(cherry picked from commit 6b82130e6c9add4a8892ca897df5a0ec04663ea2)
---
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 b571db1e27e8..a1a919bbb3b3 100644
--- a/sys/conf/files
+++ b/sys/conf/files
@@ -3905,6 +3905,7 @@ 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 08ba6c1cc838..f29dd5708230 100644
--- a/sys/kern/kern_clock.c
+++ b/sys/kern/kern_clock.c
@@ -325,7 +325,7 @@ 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 *);
@@ -371,10 +371,9 @@ 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
@@ -482,14 +481,14 @@ 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) {
@@ -498,7 +497,7 @@ 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.
@@ -527,8 +526,10 @@ 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);
@@ -542,11 +543,12 @@ 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 cee70a842735..67dc10213a70 100644
--- a/sys/kern/subr_param.c
+++ b/sys/kern/subr_param.c
@@ -198,7 +198,7 @@ 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 e07dc7031bb8..d6b5f8ec10dc 100644
--- a/sys/sys/kernel.h
+++ b/sys/sys/kernel.h
@@ -67,7 +67,16 @@ 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 fed3284e21b5..2f72f8b2527a 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