[PATCH] [PATCH]: Reset clocksource watchdog after sysrq-t

[PATCH] [PATCH]: Reset clocksource watchdog after sysrq-t

[Prarit Bhargava]

When doing a sysrq-t other processes are starved out because the task_list
lock is held.  On a large enough system this means that the clocksource
watchdog does not fire for a long time and when system operation resumes the
watchdog erroneously marks the current clocksource as unstable.

Reset the clocksource watchdog after show_state_filter() has dumped the
task states.

Cc: tglx@linutronix.de
Cc: johnstul@us.ibm.com
---
 kernel/sched.c |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)

diff --git a/kernel/sched.c b/kernel/sched.c
index d87c6e5..b09c053 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -71,6 +71,7 @@
 #include <linux/ctype.h>
 #include <linux/ftrace.h>
 #include <linux/slab.h>
+#include <linux/clocksource.h>
 
 #include <asm/tlb.h>
 #include <asm/irq_regs.h>
@@ -6034,6 +6035,7 @@ void show_state_filter(unsigned long state_filter)
 	} while_each_thread(g, p);
 
 	touch_all_softlockup_watchdogs();
+	clocksource_touch_watchdog();
 
 #ifdef CONFIG_SCHED_DEBUG
 	sysrq_sched_debug_show();
-- 
1.7.1

Re: [PATCH] [PATCH]: Reset clocksource watchdog after sysrq-t

[Xiaochen Wang]

Hi Prarit,
    I'm reading the clocksource watchdog code, in which case I see your patch.
But i cannot understand the patch very well.

On Wed, Nov 2, 2011 at 9:46 PM, Prarit Bhargava <prarit@redhat.com> wrote:
> When doing a sysrq-t other processes are starved out because the task_list
> lock is held.  On a large enough system this means that the clocksource
> watchdog does not fire for a long time and when system operation resumes the
> watchdog erroneously marks the current clocksource as unstable.
Do you mean that a sysrq-t will enlarge the deviation between watchdog and the
 watched clocksource(in watchdog_list) ?
>
> Reset the clocksource watchdog after show_state_filter() has dumped the
> task states.
>
> Cc: tglx@linutronix.de
> Cc: johnstul@us.ibm.com
> ---
>  kernel/sched.c |    2 ++
>  1 files changed, 2 insertions(+), 0 deletions(-)
>
> diff --git a/kernel/sched.c b/kernel/sched.c
> index d87c6e5..b09c053 100644
> --- a/kernel/sched.c
> +++ b/kernel/sched.c
> @@ -71,6 +71,7 @@
>  #include <linux/ctype.h>
>  #include <linux/ftrace.h>
>  #include <linux/slab.h>
> +#include <linux/clocksource.h>
>
>  #include <asm/tlb.h>
>  #include <asm/irq_regs.h>
> @@ -6034,6 +6035,7 @@ void show_state_filter(unsigned long state_filter)
>        } while_each_thread(g, p);
>
>        touch_all_softlockup_watchdogs();
> +       clocksource_touch_watchdog();
>
>  #ifdef CONFIG_SCHED_DEBUG
>        sysrq_sched_debug_show();
> --
> 1.7.1
>
> --
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Thanks,
Xiaochen