linux-kernel - [PATCH v2 21/25] timekeeping: Rework timekeeping_resume() to use shadow

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Message-Id: <20241009-devel-anna-maria-b4-timers-ptp-timekeeping-v2-21-554456a44a15@linutronix.de>
Date: Wed, 09 Oct 2024 10:29:14 +0200
From: Anna-Maria Behnsen <anna-maria@...utronix.de>
To: John Stultz <jstultz@...gle.com>, 
 Frederic Weisbecker <frederic@...nel.org>, 
 Thomas Gleixner <tglx@...utronix.de>
Cc: linux-kernel@...r.kernel.org, netdev@...r.kernel.org, 
 Miroslav Lichvar <mlichvar@...hat.com>, 
 Richard Cochran <richardcochran@...il.com>, 
 Christopher S Hall <christopher.s.hall@...el.com>, 
 Anna-Maria Behnsen <anna-maria@...utronix.de>
Subject: [PATCH v2 21/25] timekeeping: Rework timekeeping_resume() to use
 shadow_timekeeper

From: Anna-Maria Behnsen <anna-maria@...utronix.de>

Updates of the timekeeper can be done by operating on the shadow timekeeper
and afterwards copying the result into the real timekeeper. This has the
advantage, that the sequence count write protected region is kept as small
as possible.

While the sequence count held time is not relevant for the resume path as
there is no concurrency, there is no reason to have this function
different than all the other update sites.

Convert timekeeping_inject_offset() to use this scheme and cleanup the
variable declaration while at it.

Signed-off-by: Anna-Maria Behnsen <anna-maria@...utronix.de>
---
 kernel/time/timekeeping.c | 10 ++++------
 1 file changed, 4 insertions(+), 6 deletions(-)

diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index c1a2726a0d41..63b7a1379ae8 100644
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -1912,12 +1912,12 @@ void timekeeping_inject_sleeptime64(const struct timespec64 *delta)
  */
 void timekeeping_resume(void)
 {
-	struct timekeeper *tk = &tk_core.timekeeper;
+	struct timekeeper *tk = &tk_core.shadow_timekeeper;
 	struct clocksource *clock = tk->tkr_mono.clock;
-	unsigned long flags;
 	struct timespec64 ts_new, ts_delta;
-	u64 cycle_now, nsec;
 	bool inject_sleeptime = false;
+	u64 cycle_now, nsec;
+	unsigned long flags;
 
 	read_persistent_clock64(&ts_new);
 
@@ -1925,7 +1925,6 @@ void timekeeping_resume(void)
 	clocksource_resume();
 
 	raw_spin_lock_irqsave(&tk_core.lock, flags);
-	write_seqcount_begin(&tk_core.seq);
 
 	/*
 	 * After system resumes, we need to calculate the suspended time and
@@ -1960,8 +1959,7 @@ void timekeeping_resume(void)
 
 	tk->ntp_error = 0;
 	timekeeping_suspended = 0;
-	timekeeping_update(&tk_core, tk, TK_MIRROR | TK_CLOCK_WAS_SET);
-	write_seqcount_end(&tk_core.seq);
+	timekeeping_update_staged(&tk_core, TK_CLOCK_WAS_SET);
 	raw_spin_unlock_irqrestore(&tk_core.lock, flags);
 
 	touch_softlockup_watchdog();

-- 
2.39.5