linux-kernel - [PATCH v13 17/18] sched: early boot clock

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Message-Id: <20180712000419.5165-18-pasha.tatashin@oracle.com>
Date:   Wed, 11 Jul 2018 20:04:18 -0400
From:   Pavel Tatashin <pasha.tatashin@...cle.com>
To:     steven.sistare@...cle.com, daniel.m.jordan@...cle.com,
        linux@...linux.org.uk, schwidefsky@...ibm.com,
        heiko.carstens@...ibm.com, john.stultz@...aro.org,
        sboyd@...eaurora.org, x86@...nel.org, linux-kernel@...r.kernel.org,
        mingo@...hat.com, tglx@...utronix.de, hpa@...or.com,
        douly.fnst@...fujitsu.com, peterz@...radead.org, prarit@...hat.com,
        feng.tang@...el.com, pmladek@...e.com, gnomes@...rguk.ukuu.org.uk,
        linux-s390@...r.kernel.org, pasha.tatashin@...cle.com,
        boris.ostrovsky@...cle.com, jgross@...e.com
Subject: [PATCH v13 17/18] sched: early boot clock

Allow sched_clock() to be used before schec_clock_init() is called.
This provides with a way to get early boot timestamps on machines with
unstable clocks.

Signed-off-by: Pavel Tatashin <pasha.tatashin@...cle.com>
---
 init/main.c          |  2 +-
 kernel/sched/clock.c | 10 +++++++++-
 2 files changed, 10 insertions(+), 2 deletions(-)

diff --git a/init/main.c b/init/main.c
index 162d931c9511..ff0a24170b95 100644
--- a/init/main.c
+++ b/init/main.c
@@ -642,7 +642,6 @@ asmlinkage __visible void __init start_kernel(void)
 	softirq_init();
 	timekeeping_init();
 	time_init();
-	sched_clock_init();
 	printk_safe_init();
 	perf_event_init();
 	profile_init();
@@ -697,6 +696,7 @@ asmlinkage __visible void __init start_kernel(void)
 	acpi_early_init();
 	if (late_time_init)
 		late_time_init();
+	sched_clock_init();
 	calibrate_delay();
 	pid_idr_init();
 	anon_vma_init();
diff --git a/kernel/sched/clock.c b/kernel/sched/clock.c
index 3b02be1fdfda..4d07b785d566 100644
--- a/kernel/sched/clock.c
+++ b/kernel/sched/clock.c
@@ -201,7 +201,15 @@ static void __sched_clock_gtod_offset(void)
 
 void __init sched_clock_init(void)
 {
+	unsigned long flags;
+
 	sched_clock_running = 1;
+
+	/* Adjust __gtod_offset for contigious transition from early clock */
+	local_irq_save(flags);
+	sched_clock_tick();
+	local_irq_restore(flags);
+	__sched_clock_gtod_offset();
 }
 /*
  * We run this as late_initcall() such that it runs after all built-in drivers,
@@ -355,7 +363,7 @@ u64 sched_clock_cpu(int cpu)
 		return sched_clock() + __sched_clock_offset;
 
 	if (unlikely(!sched_clock_running))
-		return 0ull;
+		return sched_clock();
 
 	preempt_disable_notrace();
 	scd = cpu_sdc(cpu);
-- 
2.18.0