linux-kernel - [PATCH v8 11/12] sched: add need-resched timed wait interface

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Message-Id: <20251215044919.460086-12-ankur.a.arora@oracle.com>
Date: Sun, 14 Dec 2025 20:49:18 -0800
From: Ankur Arora <ankur.a.arora@...cle.com>
To: linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-pm@...r.kernel.org,
        bpf@...r.kernel.org
Cc: arnd@...db.de, catalin.marinas@....com, will@...nel.org,
        peterz@...radead.org, akpm@...ux-foundation.org, mark.rutland@....com,
        harisokn@...zon.com, cl@...two.org, ast@...nel.org, rafael@...nel.org,
        daniel.lezcano@...aro.org, memxor@...il.com, zhenglifeng1@...wei.com,
        xueshuai@...ux.alibaba.com, joao.m.martins@...cle.com,
        boris.ostrovsky@...cle.com, konrad.wilk@...cle.com,
        Ankur Arora <ankur.a.arora@...cle.com>, Ingo Molnar <mingo@...nel.org>
Subject: [PATCH v8 11/12] sched: add need-resched timed wait interface

Add tif_bitset_relaxed_wait() (and tif_need_resched_relaxed_wait()
which wraps it) which takes the thread_info bit and timeout duration
as parameters and waits until the bit is set or for the expiration
of the timeout.

The wait is implemented via smp_cond_load_relaxed_timeout().

smp_cond_load_acquire_timeout() essentially provides the pattern used
in poll_idle() where we spin in a loop waiting for the flag to change
until a timeout occurs.

tif_need_resched_relaxed_wait() allows us to abstract out the internals
of waiting, scheduler specific details etc.

Placed in linux/sched/idle.h instead of linux/thread_info.h to work
around recursive include hell.

Cc: Ingo Molnar <mingo@...nel.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: "Rafael J. Wysocki" <rafael@...nel.org>
Cc: Daniel Lezcano <daniel.lezcano@...aro.org>
Cc: linux-pm@...r.kernel.org
Signed-off-by: Ankur Arora <ankur.a.arora@...cle.com>
---
 include/linux/sched/idle.h | 29 +++++++++++++++++++++++++++++
 1 file changed, 29 insertions(+)

diff --git a/include/linux/sched/idle.h b/include/linux/sched/idle.h
index 8465ff1f20d1..6780ad760abb 100644
--- a/include/linux/sched/idle.h
+++ b/include/linux/sched/idle.h
@@ -3,6 +3,7 @@
 #define _LINUX_SCHED_IDLE_H
 
 #include <linux/sched.h>
+#include <linux/sched/clock.h>
 
 enum cpu_idle_type {
 	__CPU_NOT_IDLE = 0,
@@ -113,4 +114,32 @@ static __always_inline void current_clr_polling(void)
 }
 #endif
 
+/*
+ * Caller needs to make sure that the thread context cannot be preempted
+ * or migrated, so current_thread_info() cannot change from under us.
+ *
+ * This also allows us to safely stay in the local_clock domain.
+ */
+static inline bool tif_bitset_relaxed_wait(int bit, s64 timeout_ns)
+{
+	unsigned int flags;
+
+	flags = smp_cond_load_relaxed_timeout(&current_thread_info()->flags,
+					      (VAL & bit),
+					      (s64)local_clock_noinstr(),
+					      timeout_ns);
+	return flags & bit;
+}
+
+/**
+ * tif_need_resched_relaxed_wait() - Wait for need-resched being set with
+ * no ordering guarantees until a timeout expires.
+ *
+ * @timeout_ns: timeout value.
+ */
+static inline bool tif_need_resched_relaxed_wait(s64 timeout_ns)
+{
+	return tif_bitset_relaxed_wait(TIF_NEED_RESCHED, timeout_ns);
+}
+
 #endif /* _LINUX_SCHED_IDLE_H */
-- 
2.31.1