linux-kernel - [patch 3/8] timerfd: Provide timerfd

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Date:   Tue, 27 Apr 2021 10:25:40 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     LKML <linux-kernel@...r.kernel.org>
Cc:     Anna-Maria Behnsen <anna-maria@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Marcelo Tosatti <mtosatti@...hat.com>,
        Frederic Weisbecker <frederic@...nel.org>,
        Peter Xu <peterx@...hat.com>,
        Nitesh Narayan Lal <nitesh@...hat.com>,
        Alex Belits <abelits@...vell.com>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        John Stultz <john.stultz@...aro.org>
Subject: [patch 3/8] timerfd: Provide timerfd_resume()

Resuming timekeeping is a clock-was-set event and uses the clock-was-set
notification mechanism. This is in the way of making the clock-was-set
update for hrtimers selective so unnecessary IPIs are avoided when a CPU
base does not have timers queued which are affected by the clock setting.

Provide a seperate timerfd_resume() interface so the resume logic and the
clock-was-set mechanism can be distangled in the core code.

Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
---
 fs/timerfd.c            |   16 ++++++++++++++++
 include/linux/hrtimer.h |    2 ++
 2 files changed, 18 insertions(+)

--- a/fs/timerfd.c
+++ b/fs/timerfd.c
@@ -115,6 +115,22 @@ void timerfd_clock_was_set(void)
 	rcu_read_unlock();
 }
 
+static void timerfd_resume_work(struct work_struct *work)
+{
+	timerfd_clock_was_set();
+}
+
+static DECLARE_WORK(timerfd_work, timerfd_resume_work);
+
+/*
+ * Invoked from timekeeping_resume(). Defer the actual update to work so
+ * timerfd_clock_was_set() runs in task context.
+ */
+void timerfd_resume(void)
+{
+	schedule_work(&timerfd_work);
+}
+
 static void __timerfd_remove_cancel(struct timerfd_ctx *ctx)
 {
 	if (ctx->might_cancel) {
--- a/include/linux/hrtimer.h
+++ b/include/linux/hrtimer.h
@@ -349,8 +349,10 @@ hrtimer_expires_remaining_adjusted(const
 
 #ifdef CONFIG_TIMERFD
 extern void timerfd_clock_was_set(void);
+extern void timerfd_resume(void);
 #else
 static inline void timerfd_clock_was_set(void) { }
+static inline void timerfd_resume(void) { }
 #endif
 extern void hrtimers_resume(void);