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    SubjectRe: PATCH: softlockup: Fix hung_task_check_count sysctl
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    On Mon, Nov 30, 2009 at 11:13 AM, Mandeep Singh Baines <msb@google.com> wrote:
    > To disable hung_task at runtime:
    >
    > # echo 0 > /proc/sys/kernel/hung_task_check_count
    >

    D'oh. Copy and paste error. I meant

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

    The nice thing about hung_task_timeout_secs=0 is that hungtaskd will
    no longer run. Implementing
    no checking done with hung_task_check_count=0 would result in the task
    getting scheduled,
    running, and then doing nothing.

    > 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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