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Message-ID: <20250823041925.153091-1-v-singh1@ti.com>
Date: Sat, 23 Aug 2025 09:49:25 +0530
From: vishnu singh <v-singh1@...com>
To: <mark.rutland@....com>, <maz@...nel.org>, <catalin.marinas@....com>,
<will@...nel.org>, <jstultz@...gle.com>, <Ttglx@...utronix.de>,
<sboyd@...nel.org>, <akpm@...ux-foundation.org>,
<chenhuacai@...nel.org>, <pmladek@...e.com>, <agordeev@...ux.ibm.com>,
<bigeasy@...utronix.de>, <urezki@...il.com>, <Llillian@...r-ark.net>,
<francesco@...la.it>, <guoweikang.kernel@...il.com>,
<alexander.shishkin@...ux.intel.com>, <rrangel@...omium.org>,
<kpsingh@...nel.org>, <anna-maria@...utronix.de>, <mingo@...nel.org>,
<frederic@...nel.org>, <boe@...nel.org>,
<linux-kernel@...r.kernel.org>, <linux-arm-kernel@...ts.infradead.org>
Subject: [RFC PATCH] time: introduce BOOT_TIME_TRACKER and minimal boot timestamp
From: Vishnu Singh <v-singh1@...com>
Part of BOOT SIG Initiative, This patch adds a tiny,opt-in facility to
help measure kernel boot duration without full tracing:
New CONFIG_BOOT_TIME_TRACKER in kernel/time/Kconfig.
When enabled, the kernel logs two boot markers:
1. kernel entry in start_kernel()
2. first userspace start in kernel_init() before run_init_process()
These markers are intended for post-boot parsers to compute coarse
kernel boot time and to merge with bootloader/MCU/DSP records into
a unified timeline.
Core helper u64 boot_time_now() in kernel/time/boot_time_now.c,
exporting a counter‑derived timestamp via small per-arch primitives.
This series includes an initial arm64 primitive that uses CNTVCT_EL0
as the source, other architectures can wire up equivalents.
Files touched:
kernel/time/Kconfig, kernel/time/Makefile
kernel/time/boot_time_now.c (new core helper)
arch/arm64/include/asm/boot_time_primitives.h (arm64 primitive)
include/linux/boot_time_now.h (public API + IDs)
init/main.c (print two markers)
This complements U-Boot’s stashed bootstage records so a userspace tool
can build a system-wide boot timeline across SPL, U-Boot, kernel and other
subsystems.
Reference boot-time parser utility:
https://github.com/v-singh1/boot-time-parser
Sample boot time report:
+--------------------------------------------------------------------+
am62xx-evm Boot Time Report
+--------------------------------------------------------------------+
Device Power On : 0 ms
SPL Time : 843 ms
U-Boot Time : 2173 ms
Kernel handoff time : 462 ms
Kernel Time : 2522 ms
Total Boot Time : 6000 ms
+--------------------------------------------------------------------+
+--------------------------------------------------------------------+
Bootloader and Kernel Boot Records
+--------------------------------------------------------------------+
BOOTSTAGE_AWAKE = 0 ms (+ 0 ms)
BOOTSTAGE_START_UBOOT_F = 843 ms (+ 0 ms)
BOOTSTAGE_ACCUM_DM_F = 843 ms (+ 0 ms)
BOOTSTAGE_START_UBOOT_R = 1951 ms (+1108 ms)
BOOTSTAGE_ACCUM_DM_R = 1951 ms (+ 0 ms)
BOOTSTAGE_NET_ETH_START = 2032 ms (+ 81 ms)
BOOTSTAGE_NET_ETH_INIT = 2053 ms (+ 21 ms)
BOOTSTAGE_MAIN_LOOP = 2055 ms (+ 2 ms)
BOOTSTAGE_START_MCU = 2661 ms (+606 ms)
BOOTSTAGE_BOOTM_START = 2959 ms (+298 ms)
BOOTSTAGE_RUN_OS = 3016 ms (+ 57 ms)
BOOTSTAGE_BOOTM_HANDOFF = 3016 ms (+ 0 ms)
BOOTSTAGE_KERNEL_START = 3478 ms (+462 ms)
BOOTSTAGE_KERNEL_END = 6000 ms (+2522 ms)
+--------------------------------------------------------------------+
+--------------------------------------------------------------------+
MCU Boot Records
+--------------------------------------------------------------------+
MCU_AWAKE = 2661 ms (+ 0 ms)
BOARD_PERIPHERALS_INIT = 2661 ms (+ 0 ms)
MAIN_TASK_CREATE = 2661 ms (+ 0 ms)
FIRST_TASK = 2662 ms (+ 1 ms)
DRIVERS_OPEN = 2662 ms (+ 0 ms)
BOARD_DRIVERS_OPEN = 2662 ms (+ 0 ms)
IPC_SYNC_FOR_LINUX = 6636 ms (+3974 ms)
IPC_REGISTER_CLIENT = 6636 ms (+ 0 ms)
IPC_SUSPEND_TASK = 6636 ms (+ 0 ms)
IPC_RECEIVE_TASK = 6636 ms (+ 0 ms)
IPC_SYNC_ALL = 6787 ms (+151 ms)
+--------------------------------------------------------------------+
Signed-off-by: Vishnu Singh <v-singh1@...com>
---
MAINTAINERS | 3 +++
arch/arm64/include/asm/boot_time_primitives.h | 14 ++++++++++++++
include/linux/boot_time_now.h | 16 ++++++++++++++++
init/main.c | 13 +++++++++++++
kernel/time/Kconfig | 10 ++++++++++
kernel/time/Makefile | 1 +
kernel/time/boot_time_now.c | 13 +++++++++++++
7 files changed, 70 insertions(+)
create mode 100644 arch/arm64/include/asm/boot_time_primitives.h
create mode 100644 include/linux/boot_time_now.h
create mode 100644 kernel/time/boot_time_now.c
diff --git a/MAINTAINERS b/MAINTAINERS
index e913c1edd1fd..e5273b338814 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -1994,6 +1994,7 @@ L: linux-arm-kernel@...ts.infradead.org (moderated for non-subscribers)
S: Maintained
F: arch/arm/include/asm/arch_timer.h
F: arch/arm64/include/asm/arch_timer.h
+F: arch/arm64/include/asm/boot_time_primitives.h
F: drivers/clocksource/arm_arch_timer.c
F: drivers/clocksource/arm_arch_timer_mmio.c
@@ -25466,6 +25467,7 @@ R: Stephen Boyd <sboyd@...nel.org>
L: linux-kernel@...r.kernel.org
S: Supported
T: git git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git timers/core
+F: include/linux/boot_time_now.h
F: include/linux/clocksource.h
F: include/linux/time.h
F: include/linux/timekeeper_internal.h
@@ -25474,6 +25476,7 @@ F: include/linux/timex.h
F: include/uapi/linux/time.h
F: include/uapi/linux/timex.h
F: kernel/time/alarmtimer.c
+F: kernel/time/boot_time_now.c
F: kernel/time/clocksource*
F: kernel/time/ntp*
F: kernel/time/time.c
diff --git a/arch/arm64/include/asm/boot_time_primitives.h b/arch/arm64/include/asm/boot_time_primitives.h
new file mode 100644
index 000000000000..9bbbd500a95d
--- /dev/null
+++ b/arch/arm64/include/asm/boot_time_primitives.h
@@ -0,0 +1,14 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+#ifndef __ASM_BOOT_TIME_PRIMITIVES_H
+#define __ASM_BOOT_TIME_PRIMITIVES_H
+
+#include <asm/arch_timer.h>
+#include <linux/math64.h>
+
+static inline u64 arch_boot_counter_now(void)
+{
+ return ((arch_timer_read_cntvct_el0() * 1000000) / arch_timer_get_cntfrq());
+}
+
+#endif
diff --git a/include/linux/boot_time_now.h b/include/linux/boot_time_now.h
new file mode 100644
index 000000000000..a18a1809057f
--- /dev/null
+++ b/include/linux/boot_time_now.h
@@ -0,0 +1,16 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+#ifndef _LINUX_BOOT_TRACKER_H
+#define _LINUX_BOOT_TRACKER_H
+
+#include <linux/types.h>
+
+enum kernel_bootstage_id {
+ BOOTSTAGE_ID_KERNEL_START = 300,
+ BOOTSTAGE_ID_KERNEL_END = 301,
+};
+
+/* Return boot time in nanoseconds using hardware counter */
+u64 boot_time_now(void);
+
+#endif
diff --git a/init/main.c b/init/main.c
index 9b5150166bcf..76eb8098ab20 100644
--- a/init/main.c
+++ b/init/main.c
@@ -115,6 +115,10 @@
#include <kunit/test.h>
+#ifdef CONFIG_BOOT_TIME_TRACKER
+#include <linux/boot_time_now.h>
+#endif
+
static int kernel_init(void *);
/*
@@ -929,6 +933,11 @@ void start_kernel(void)
page_address_init();
pr_notice("%s", linux_banner);
setup_arch(&command_line);
+
+#ifdef CONFIG_BOOT_TIME_TRACKER
+ pr_info("[BOOT TRACKER] - ID:%d, %s = %llu\n",
+ BOOTSTAGE_ID_KERNEL_START, __func__, boot_time_now());
+#endif
/* Static keys and static calls are needed by LSMs */
jump_label_init();
static_call_init();
@@ -1503,6 +1512,10 @@ static int __ref kernel_init(void *unused)
do_sysctl_args();
+#ifdef CONFIG_BOOT_TIME_TRACKER
+ pr_info("[BOOT TRACKER] - ID:%d, %s = %llu\n",
+ BOOTSTAGE_ID_KERNEL_END, __func__, boot_time_now());
+#endif
if (ramdisk_execute_command) {
ret = run_init_process(ramdisk_execute_command);
if (!ret)
diff --git a/kernel/time/Kconfig b/kernel/time/Kconfig
index 7c6a52f7836c..aadfd66d5d69 100644
--- a/kernel/time/Kconfig
+++ b/kernel/time/Kconfig
@@ -221,4 +221,14 @@ config POSIX_AUX_CLOCKS
and other clock domains, which are not correlated to the TAI/NTP
notion of time.
+config BOOT_TIME_TRACKER
+ bool "boot time tracking support"
+ help
+ Prints boot timestamps at the beginning of the kernel and when the
+ first user-space process is launched. This helps measure basic
+ boot latency for embedded and multi-core systems.
+
+ The messages appear using printk and can be parsed by boot
+ instrumentation tools or console logs.
+
endmenu
diff --git a/kernel/time/Makefile b/kernel/time/Makefile
index e6e9b85d4db5..f7c115a385bb 100644
--- a/kernel/time/Makefile
+++ b/kernel/time/Makefile
@@ -32,3 +32,4 @@ obj-$(CONFIG_TEST_UDELAY) += test_udelay.o
obj-$(CONFIG_TIME_NS) += namespace.o
obj-$(CONFIG_TEST_CLOCKSOURCE_WATCHDOG) += clocksource-wdtest.o
obj-$(CONFIG_TIME_KUNIT_TEST) += time_test.o
+obj-$(CONFIG_BOOT_TIME_TRACKER) += boot_time_now.o
diff --git a/kernel/time/boot_time_now.c b/kernel/time/boot_time_now.c
new file mode 100644
index 000000000000..6dc12d454be0
--- /dev/null
+++ b/kernel/time/boot_time_now.c
@@ -0,0 +1,13 @@
+// SPDX-License-Identifier: LGPL-2.0
+
+#include <linux/boot_time_now.h>
+#include <asm/boot_time_primitives.h>
+
+u64 boot_time_now(void)
+{
+ return arch_boot_counter_now();
+}
+EXPORT_SYMBOL_GPL(boot_time_now);
+
+MODULE_DESCRIPTION("boot time tracker");
+MODULE_LICENSE("GPL");
--
2.50.1
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