linux-kernel - [PATCH 06/21] ntp: Read reference time only once

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Message-Id: <20240911-devel-anna-maria-b4-timers-ptp-ntp-v1-6-2d52f4e13476@linutronix.de>
Date: Wed, 11 Sep 2024 15:17:42 +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 06/21] ntp: Read reference time only once

From: Thomas Gleixner <tglx@...utronix.de>

The reference time is required twice in ntp_update_offset(). It will not
change in the meantime as the calling code holds the timekeeper lock. Read
it only once and store it into a local variable.

Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Signed-off-by: Anna-Maria Behnsen <anna-maria@...utronix.de>
---
 kernel/time/ntp.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/kernel/time/ntp.c b/kernel/time/ntp.c
index ef758aafdfd5..477cb08062bc 100644
--- a/kernel/time/ntp.c
+++ b/kernel/time/ntp.c
@@ -283,9 +283,8 @@ static inline s64 ntp_update_offset_fll(s64 offset64, long secs)
 
 static void ntp_update_offset(long offset)
 {
-	s64 freq_adj;
-	s64 offset64;
-	long secs;
+	s64 freq_adj, offset64;
+	long secs, real_secs;
 
 	if (!(time_status & STA_PLL))
 		return;
@@ -303,11 +302,12 @@ static void ntp_update_offset(long offset)
 	 * Select how the frequency is to be controlled
 	 * and in which mode (PLL or FLL).
 	 */
-	secs = (long)(__ktime_get_real_seconds() - time_reftime);
+	real_secs = __ktime_get_real_seconds();
+	secs = (long)(real_secs - time_reftime);
 	if (unlikely(time_status & STA_FREQHOLD))
 		secs = 0;
 
-	time_reftime = __ktime_get_real_seconds();
+	time_reftime = real_secs;
 
 	offset64    = offset;
 	freq_adj    = ntp_update_offset_fll(offset64, secs);

-- 
2.39.2