[patch 3/8] timerfd: Provide timerfd_resume()

Thomas Gleixner
2021-04-27T08:38:03Z

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@linutronix.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);