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From:   Feng Tang <feng.tang@intel.com>
To:     John Stultz <jstultz@google.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Stephen Boyd <sboyd@kernel.org>, linux-kernel@vger.kernel.org
Cc:     paulmck@kernel.org, Feng Tang <feng.tang@intel.com>
Subject: [PATCH] clocksource: Add a helper fucntion to reduce code duplication
Date:   Wed, 24 May 2023 12:07:33 +0800
Message-Id: <20230524040733.66946-1-feng.tang@intel.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

Several places use the same pattern of 'clocksource_delta() +
clocksource_cyc2ns()' for calcualating the time delta in nanoseconds
from 2 counters read from a clocksource. Add a helper function to
simplify the code.

signe-off-by: Feng Tang <feng.tang@intel.com>
---
 kernel/time/clocksource.c | 36 +++++++++++++++++++++---------------
 1 file changed, 21 insertions(+), 15 deletions(-)

diff --git a/kernel/time/clocksource.c b/kernel/time/clocksource.c
index 91836b727cef..9f9e25cf5b44 100644
--- a/kernel/time/clocksource.c
+++ b/kernel/time/clocksource.c
@@ -145,6 +145,18 @@ static inline void clocksource_watchdog_unlock(unsigned long *flags)
 	spin_unlock_irqrestore(&watchdog_lock, *flags);
 }
 
+
+/*
+ * Calculate the delta of 2 counters read from a clocksource, and convert
+ * it to nanoseconds. Intended only for short time interval calculation.
+ */
+static inline u64 calc_counters_to_delta_ns(u64 new, u64 old, struct clocksource *cs)
+{
+	u64 delta = clocksource_delta(new, old, cs->mask);
+
+	return clocksource_cyc2ns(delta, cs->mult, cs->shift);
+}
+
 static int clocksource_watchdog_kthread(void *data);
 static void __clocksource_change_rating(struct clocksource *cs, int rating);
 
@@ -223,7 +235,7 @@ enum wd_read_status {
 static enum wd_read_status cs_watchdog_read(struct clocksource *cs, u64 *csnow, u64 *wdnow)
 {
 	unsigned int nretries;
-	u64 wd_end, wd_end2, wd_delta;
+	u64 wd_end, wd_end2;
 	int64_t wd_delay, wd_seq_delay;
 
 	for (nretries = 0; nretries <= max_cswd_read_retries; nretries++) {
@@ -234,9 +246,7 @@ static enum wd_read_status cs_watchdog_read(struct clocksource *cs, u64 *csnow,
 		wd_end2 = watchdog->read(watchdog);
 		local_irq_enable();
 
-		wd_delta = clocksource_delta(wd_end, *wdnow, watchdog->mask);
-		wd_delay = clocksource_cyc2ns(wd_delta, watchdog->mult,
-					      watchdog->shift);
+		wd_delay = calc_counters_to_delta_ns(wd_end, *wdnow, watchdog);
 		if (wd_delay <= WATCHDOG_MAX_SKEW) {
 			if (nretries > 1 || nretries >= max_cswd_read_retries) {
 				pr_warn("timekeeping watchdog on CPU%d: %s retried %d times before success\n",
@@ -254,8 +264,8 @@ static enum wd_read_status cs_watchdog_read(struct clocksource *cs, u64 *csnow,
 		 * report system busy, reinit the watchdog and skip the current
 		 * watchdog test.
 		 */
-		wd_delta = clocksource_delta(wd_end2, wd_end, watchdog->mask);
-		wd_seq_delay = clocksource_cyc2ns(wd_delta, watchdog->mult, watchdog->shift);
+
+		wd_seq_delay = calc_counters_to_delta_ns(wd_end2, wd_end, watchdog);
 		if (wd_seq_delay > WATCHDOG_MAX_SKEW/2)
 			goto skip_test;
 	}
@@ -366,8 +376,8 @@ void clocksource_verify_percpu(struct clocksource *cs)
 		delta = (csnow_end - csnow_mid) & cs->mask;
 		if (delta < 0)
 			cpumask_set_cpu(cpu, &cpus_ahead);
-		delta = clocksource_delta(csnow_end, csnow_begin, cs->mask);
-		cs_nsec = clocksource_cyc2ns(delta, cs->mult, cs->shift);
+
+		cs_nsec = calc_counters_to_delta_ns(csnow_end, csnow_begin, cs);
 		if (cs_nsec > cs_nsec_max)
 			cs_nsec_max = cs_nsec;
 		if (cs_nsec < cs_nsec_min)
@@ -398,7 +408,7 @@ static inline void clocksource_reset_watchdog(void)
 
 static void clocksource_watchdog(struct timer_list *unused)
 {
-	u64 csnow, wdnow, cslast, wdlast, delta;
+	u64 csnow, wdnow, cslast, wdlast;
 	int next_cpu, reset_pending;
 	int64_t wd_nsec, cs_nsec;
 	struct clocksource *cs;
@@ -456,14 +466,10 @@ static void clocksource_watchdog(struct timer_list *unused)
 			continue;
 		}
 
-		delta = clocksource_delta(wdnow, cs->wd_last, watchdog->mask);
-		wd_nsec = clocksource_cyc2ns(delta, watchdog->mult,
-					     watchdog->shift);
-
-		delta = clocksource_delta(csnow, cs->cs_last, cs->mask);
-		cs_nsec = clocksource_cyc2ns(delta, cs->mult, cs->shift);
 		wdlast = cs->wd_last; /* save these in case we print them */
 		cslast = cs->cs_last;
+		wd_nsec = calc_counters_to_delta_ns(wdnow, wdlast, watchdog);
+		cs_nsec = calc_counters_to_delta_ns(csnow, cslast, cs);
 		cs->cs_last = csnow;
 		cs->wd_last = wdnow;
 
-- 
2.27.0