[PATCH v2 1/2] x86/tsc: add a timer to make sure tsc_adjust is always checked

[Feng Tang]

Normally the tsc_sync will get checked every time system enters idle state,
but Thomas Gleixner mentioned there is still a caveat that a system won't
enter idle [1], either because it's too busy or configured purposely to not
enter idle. Setup a periodic timer to make sure the check is always on.

[1]. https://lore.kernel.org/lkml/875z286xtk.fsf@xxxxxxxxxxxxxxxxxxxxxxx/
Signed-off-by: Feng Tang <feng.tang@xxxxxxxxx>
---
Change log:
  
  v2:
     * skip timer setup when tsc_clocksource_reliabe==1 (Thomas)
     * refine comment and code format (Thomas) 

 arch/x86/kernel/tsc_sync.c | 39 +++++++++++++++++++++++++++++++++++++++
 1 file changed, 39 insertions(+)

diff --git a/arch/x86/kernel/tsc_sync.c b/arch/x86/kernel/tsc_sync.c
index 3d3c761..39f18fa 100644
--- a/arch/x86/kernel/tsc_sync.c
+++ b/arch/x86/kernel/tsc_sync.c
@@ -30,6 +30,7 @@ struct tsc_adjust {
 };
 
 static DEFINE_PER_CPU(struct tsc_adjust, tsc_adjust);
+static struct timer_list tsc_sync_check_timer;
 
 /*
  * TSC's on different sockets may be reset asynchronously.
@@ -77,6 +78,44 @@ void tsc_verify_tsc_adjust(bool resume)
 	}
 }
 
+/*
+ * Normally the tsc_sync will be checked every time system enters idle state,
+ * but there is still caveat that a system won't enter idle, either because
+ * it's too busy or configured purposely to not enter idle.
+ *
+ * So setup a periodic timer to make sure the check is always on.
+ */
+
+#define SYNC_CHECK_INTERVAL		(HZ * 600)
+
+static void tsc_sync_check_timer_fn(struct timer_list *unused)
+{
+	int next_cpu;
+
+	tsc_verify_tsc_adjust(false);
+
+	/* Run the check for all onlined CPUs in turn */
+	next_cpu = cpumask_next(raw_smp_processor_id(), cpu_online_mask);
+	if (next_cpu >= nr_cpu_ids)
+		next_cpu = cpumask_first(cpu_online_mask);
+
+	tsc_sync_check_timer.expires += SYNC_CHECK_INTERVAL;
+	add_timer_on(&tsc_sync_check_timer, next_cpu);
+}
+
+static int __init start_sync_check_timer(void)
+{
+	if (!boot_cpu_has(X86_FEATURE_TSC_ADJUST) || tsc_clocksource_reliable)
+		return 0;
+
+	timer_setup(&tsc_sync_check_timer, tsc_sync_check_timer_fn, 0);
+	tsc_sync_check_timer.expires = jiffies + SYNC_CHECK_INTERVAL;
+	add_timer(&tsc_sync_check_timer);
+
+	return 0;
+}
+late_initcall(start_sync_check_timer);
+
 static void tsc_sanitize_first_cpu(struct tsc_adjust *cur, s64 bootval,
 				   unsigned int cpu, bool bootcpu)
 {
-- 
2.7.4