[tip: sched/hrtick] x86: Inline TSC reads in timekeeping

[tip-bot2 for Thomas Gleixner]

The following commit has been merged into the sched/hrtick branch of tip:

Commit-ID:     b27801189f7fc97a960a96a63b78dcabbb67a52f
Gitweb:        https://git.kernel.org/tip/b27801189f7fc97a960a96a63b78dcabbb67a52f
Author:        Thomas Gleixner <tglx@xxxxxxxxxx>
AuthorDate:    Tue, 24 Feb 2026 17:36:24 +01:00
Committer:     Peter Zijlstra <peterz@xxxxxxxxxxxxx>
CommitterDate: Fri, 27 Feb 2026 16:40:07 +01:00

x86: Inline TSC reads in timekeeping

Avoid the overhead of the indirect call for a single instruction to read
the TSC.

Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Link: https://patch.msgid.link/20260224163429.741886362@xxxxxxxxxx
---
 arch/x86/Kconfig                     |  1 +
 arch/x86/include/asm/clock_inlined.h | 14 ++++++++++++++
 arch/x86/kernel/tsc.c                |  1 +
 3 files changed, 16 insertions(+)
 create mode 100644 arch/x86/include/asm/clock_inlined.h

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index e2df1b1..d337d8d 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -141,6 +141,7 @@ config X86
 	select ARCH_USE_SYM_ANNOTATIONS
 	select ARCH_WANT_BATCHED_UNMAP_TLB_FLUSH
 	select ARCH_WANT_DEFAULT_BPF_JIT	if X86_64
+	select ARCH_WANTS_CLOCKSOURCE_READ_INLINE	if X86_64
 	select ARCH_WANTS_DYNAMIC_TASK_STRUCT
 	select ARCH_WANTS_NO_INSTR
 	select ARCH_WANT_GENERAL_HUGETLB
diff --git a/arch/x86/include/asm/clock_inlined.h b/arch/x86/include/asm/clock_inlined.h
new file mode 100644
index 0000000..29902c5
--- /dev/null
+++ b/arch/x86/include/asm/clock_inlined.h
@@ -0,0 +1,14 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _ASM_X86_CLOCK_INLINED_H
+#define _ASM_X86_CLOCK_INLINED_H
+
+#include <asm/tsc.h>
+
+struct clocksource;
+
+static __always_inline u64 arch_inlined_clocksource_read(struct clocksource *cs)
+{
+	return (u64)rdtsc_ordered();
+}
+
+#endif
diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
index d9aa694..74a26fb 100644
--- a/arch/x86/kernel/tsc.c
+++ b/arch/x86/kernel/tsc.c
@@ -1201,6 +1201,7 @@ static struct clocksource clocksource_tsc = {
 	.mask			= CLOCKSOURCE_MASK(64),
 	.flags			= CLOCK_SOURCE_IS_CONTINUOUS |
 				  CLOCK_SOURCE_VALID_FOR_HRES |
+				  CLOCK_SOURCE_CAN_INLINE_READ |
 				  CLOCK_SOURCE_MUST_VERIFY |
 				  CLOCK_SOURCE_VERIFY_PERCPU,
 	.id			= CSID_X86_TSC,