linux-kernel - [PATCH x86] [1/16] Make clocksource watchdog cycle through online CPUs

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Date:	Thu,  3 Jan 2008 16:42:14 +0100 (CET)
From:	Andi Kleen <ak@...e.de>
To:	tglx@...utronix.de, linux-kernel@...r.kernel.org
Subject: [PATCH x86] [1/16] Make clocksource watchdog cycle through online CPUs


This way it checks if the clocks are synchronized between CPUs too.
This might be able to detect slowly drifting TSCs which only
go wrong over longer time.

Cc: tglx@...utronix.de

Signed-off-by: Andi Kleen <ak@...e.de>

---
 kernel/time/clocksource.c |   14 ++++++++++----
 1 file changed, 10 insertions(+), 4 deletions(-)

Index: linux/kernel/time/clocksource.c
===================================================================
--- linux.orig/kernel/time/clocksource.c
+++ linux/kernel/time/clocksource.c
@@ -142,8 +142,13 @@ static void clocksource_watchdog(unsigne
 	}
 
 	if (!list_empty(&watchdog_list)) {
-		__mod_timer(&watchdog_timer,
-			    watchdog_timer.expires + WATCHDOG_INTERVAL);
+		/* Cycle through CPUs to check if the CPUs stay synchronized to
+		 * each other. */
+		int next_cpu = next_cpu(raw_smp_processor_id(), cpu_online_map);
+		if (next_cpu >= NR_CPUS)
+			next_cpu = first_cpu(cpu_online_map);
+		watchdog_timer.expires += WATCHDOG_INTERVAL;
+		add_timer_on(&watchdog_timer, next_cpu);
 	}
 	spin_unlock(&watchdog_lock);
 }
@@ -165,7 +170,7 @@ static void clocksource_check_watchdog(s
 		if (!started && watchdog) {
 			watchdog_last = watchdog->read();
 			watchdog_timer.expires = jiffies + WATCHDOG_INTERVAL;
-			add_timer(&watchdog_timer);
+			add_timer_on(&watchdog_timer, first_cpu(cpu_online_map));
 		}
 	} else {
 		if (cs->flags & CLOCK_SOURCE_IS_CONTINUOUS)
@@ -186,7 +191,8 @@ static void clocksource_check_watchdog(s
 				watchdog_last = watchdog->read();
 				watchdog_timer.expires =
 					jiffies + WATCHDOG_INTERVAL;
-				add_timer(&watchdog_timer);
+				add_timer_on(&watchdog_timer,
+						first_cpu(cpu_online_map));
 			}
 		}
 	}
--
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