[PATCH] Time: Delay clocksource selection until later in boot

[PATCH] Time: Delay clocksource selection until later in boot

[john stultz]

	Delay installing new clocksources until later in boot. This avoids some
of the clocksource churn that can occur at boot, possibly allowing the
system to run for a brief time with a bad clocksource.

This patch resolves the boot time stalls seen by Mattia Dongili.

thanks
-john

Signed-off-by: John Stultz <johnstul@us.ibm.com>


diff --git a/kernel/time/clocksource.c b/kernel/time/clocksource.c
--- a/kernel/time/clocksource.c
+++ b/kernel/time/clocksource.c
@@ -51,13 +51,27 @@ static LIST_HEAD(clocksource_list);
 static DEFINE_SPINLOCK(clocksource_lock);
 static char override_name[32];
 
+static int finished_booting;
+
+/* clocksource_done_booting - Called near the end of bootup
+ *
+ * Hack to avoid lots of clocksource churn at boot time 
+ */
+static int clocksource_done_booting(void)
+{
+	finished_booting = 1;
+	return 0;
+}
+
+late_initcall(clocksource_done_booting);
+
 /**
  * get_next_clocksource - Returns the selected clocksource
  */
 struct clocksource *get_next_clocksource(void)
 {
 	spin_lock(&clocksource_lock);
-	if (next_clocksource) {
+	if (next_clocksource && finished_booting) {
 		curr_clocksource = next_clocksource;
 		next_clocksource = NULL;
 	}

Re: [PATCH] Time: Delay clocksource selection until later in boot

[Andrew Morton]

john stultz <johnstul@us.ibm.com> wrote:
>
> 	Delay installing new clocksources until later in boot. This avoids some
> of the clocksource churn that can occur at boot, possibly allowing the
> system to run for a brief time with a bad clocksource.
> 
> This patch resolves the boot time stalls seen by Mattia Dongili.
> 

Except he now thinks that it doesn't.  Do you think the patch is good anyway?

Re: [PATCH] Time: Delay clocksource selection until later in boot

[john stultz]

On Tue, 2006-01-17 at 15:43 -0800, Andrew Morton wrote:
> john stultz <johnstul@us.ibm.com> wrote:
> >
> > 	Delay installing new clocksources until later in boot. This avoids some
> > of the clocksource churn that can occur at boot, possibly allowing the
> > system to run for a brief time with a bad clocksource.
> > 
> > This patch resolves the boot time stalls seen by Mattia Dongili.
> > 
> 
> Except he now thinks that it doesn't.  Do you think the patch is good anyway?

I actually do still think its a good idea to avoid the bootup
clocksource churn. I've still got a few ideas for further improving the
TSC registration so I'll probably have another patch or two to try later
this week.

thanks
-john