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SubjectRe: PATCH: softlockup: Fix hung_task_check_count sysctl
To disable hung_task at runtime:

# echo 0 > /proc/sys/kernel/hung_task_check_count

33 /*
34 * Zero means infinite timeout - no checking done:
35 */
36 unsigned long __read_mostly sysctl_hung_task_timeout_secs = 120;

For hung_task_check_count, 0 means there is no maximum so all tasks
are checked.

Anton Blanchard (anton@samba.org) wrote:
>
> I'm seeing spikes of up to 0.5ms in khungtaskd on a large machine. To reduce
> this source of jitter I tried setting hung_task_check_count to 0:
>

Hmm, maybe khungtaskd should be run using SCHED_IDLE.

> # echo 0 > /proc/sys/kernel/hung_task_check_count
>
> which didn't have the intended response. Change to a post increment of
> max_count, so a value of 0 means check 0 tasks.
>
> Signed-off-by: Anton Blanchard <anton@samba.org>
> ---
>
> Index: linux.trees.git/kernel/hung_task.c
> ===================================================================
> --- linux.trees.git.orig/kernel/hung_task.c 2009-11-27 13:11:46.000000000 +1100
> +++ linux.trees.git/kernel/hung_task.c 2009-11-27 13:11:57.000000000 +1100
> @@ -144,7 +144,7 @@ static void check_hung_uninterruptible_t
>
> rcu_read_lock();
> do_each_thread(g, t) {
> - if (!--max_count)
> + if (!max_count--)
> goto unlock;
> if (!--batch_count) {
> batch_count = HUNG_TASK_BATCHING;


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