linux-kernel - Re: [RFC][PATCH -rt] Handling delayed clocksource watchdog timer

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Date:	Thu, 22 Jul 2010 20:34:14 -0700
From:	john stultz <johnstul@...ibm.com>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	lkml <linux-kernel@...r.kernel.org>,
	Darren Hart <dvhltc@...ibm.com>,
	Paul Clarke <pacman@...ibm.com>
Subject: Re: [RFC][PATCH -rt] Handling delayed clocksource watchdog timer

On Thu, 2010-07-22 at 20:13 -0700, john stultz wrote:
> diff --git a/kernel/time/clocksource.c b/kernel/time/clocksource.c
> index 0e98497..a91e7ba 100644
> --- a/kernel/time/clocksource.c
> +++ b/kernel/time/clocksource.c
> @@ -280,7 +280,8 @@ static void clocksource_watchdog(unsigned long data)
>  		cs_nsec = clocksource_cyc2ns((csnow - cs->wd_last) &
>  					     cs->mask, cs->mult, cs->shift);
>  		cs->wd_last = csnow;
> -		if (abs(cs_nsec - wd_nsec) > WATCHDOG_THRESHOLD) {
> +		if (jiffies - watchdog_timer.expires > 4*WATCHDOG_INTERVAL) &&
> +				(abs(cs_nsec - wd_nsec) > WATCHDOG_THRESHOLD) {
>  			clocksource_unstable(cs, cs_nsec - wd_nsec);
>  			continue;
>  		}


Bah. 

Was testing with this patch and just realized it has a thinko
(greater-than instead of less-than).

Should be:

diff --git a/kernel/time/clocksource.c b/kernel/time/clocksource.c
index 0e98497..a91e7ba 100644
--- a/kernel/time/clocksource.c
+++ b/kernel/time/clocksource.c
@@ -280,7 +280,8 @@ static void clocksource_watchdog(unsigned long data)
 		cs_nsec = clocksource_cyc2ns((csnow - cs->wd_last) &
 					     cs->mask, cs->mult, cs->shift);
 		cs->wd_last = csnow;
-		if (abs(cs_nsec - wd_nsec) > WATCHDOG_THRESHOLD) {
+		if (jiffies - watchdog_timer.expires < 4*WATCHDOG_INTERVAL) &&
+				(abs(cs_nsec - wd_nsec) > WATCHDOG_THRESHOLD) {
 			clocksource_unstable(cs, cs_nsec - wd_nsec);
 			continue;
 		}


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