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    Subject[PATCH 4/4] watchdog: configure nmi watchdog period based on watchdog_thresh
    Date
    Before the conversion of the NMI watchdog to perf event, the watchdog
    timeout was 5 seconds. Now it is 60 seconds. For my particular application,
    netbooks, 5 seconds was a better timeout. With a short timeout, we
    catch faults earlier and are able to send back a panic. With a 60 second
    timeout, the user is unlikely to wait and will instead hit the power
    button, causing us to lose the panic info.

    This change configures the NMI period to watchdog_thresh and sets
    the softlockup_thresh to watchdog_thresh * 2. In addition, watchdog_thresh
    was reduced to 10 seconds as suggested by Ingo Molnar.

    Signed-off-by: Mandeep Singh Baines <msb@chromium.org>
    LKML-Reference: <20110517071642.GF22305@elte.hu>
    Cc: Marcin Slusarz <marcin.slusarz@gmail.com>
    Cc: Don Zickus <dzickus@redhat.com>
    Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
    Cc: Frederic Weisbecker <fweisbec@gmail.com>
    Cc: Ingo Molnar <mingo@elte.hu>
    Cc: Andrew Morton <akpm@linux-foundation.org>
    ---
    arch/x86/kernel/apic/hw_nmi.c | 4 ++--
    include/linux/nmi.h | 2 +-
    kernel/watchdog.c | 19 +++++++++++++++----
    3 files changed, 18 insertions(+), 7 deletions(-)

    diff --git a/arch/x86/kernel/apic/hw_nmi.c b/arch/x86/kernel/apic/hw_nmi.c
    index 5260fe9..d5e57db0 100644
    --- a/arch/x86/kernel/apic/hw_nmi.c
    +++ b/arch/x86/kernel/apic/hw_nmi.c
    @@ -19,9 +19,9 @@
    #include <linux/delay.h>

    #ifdef CONFIG_HARDLOCKUP_DETECTOR
    -u64 hw_nmi_get_sample_period(void)
    +u64 hw_nmi_get_sample_period(int watchdog_thresh)
    {
    - return (u64)(cpu_khz) * 1000 * 60;
    + return (u64)(cpu_khz) * 1000 * watchdog_thresh;
    }
    #endif

    diff --git a/include/linux/nmi.h b/include/linux/nmi.h
    index 5317b8b..2d304ef 100644
    --- a/include/linux/nmi.h
    +++ b/include/linux/nmi.h
    @@ -45,7 +45,7 @@ static inline bool trigger_all_cpu_backtrace(void)

    #ifdef CONFIG_LOCKUP_DETECTOR
    int hw_nmi_is_cpu_stuck(struct pt_regs *);
    -u64 hw_nmi_get_sample_period(void);
    +u64 hw_nmi_get_sample_period(int watchdog_thresh);
    extern int watchdog_enabled;
    extern int watchdog_thresh;
    struct ctl_table;
    diff --git a/kernel/watchdog.c b/kernel/watchdog.c
    index 6030191..6e63097 100644
    --- a/kernel/watchdog.c
    +++ b/kernel/watchdog.c
    @@ -28,7 +28,7 @@
    #include <linux/perf_event.h>

    int watchdog_enabled = 1;
    -int __read_mostly watchdog_thresh = 60;
    +int __read_mostly watchdog_thresh = 10;

    static DEFINE_PER_CPU(unsigned long, watchdog_touch_ts);
    static DEFINE_PER_CPU(struct task_struct *, softlockup_watchdog);
    @@ -91,6 +91,17 @@ static int __init nosoftlockup_setup(char *str)
    __setup("nosoftlockup", nosoftlockup_setup);
    /* */

    +/*
    + * Hard-lockup warnings should be triggered after just a few seconds. Soft-
    + * lockups can have false positives under extreme conditions. So we generally
    + * want a higher threshold for soft lockups than for hard lockups. So we couple
    + * the thresholds with a factor: we make the soft threshold twice the amount of
    + * time the hard threshold is.
    + */
    +static int get_softlockup_thresh()
    +{
    + return watchdog_thresh * 2;
    +}

    /*
    * Returns seconds, approximately. We don't need nanosecond
    @@ -110,7 +121,7 @@ static unsigned long get_sample_period(void)
    * increment before the hardlockup detector generates
    * a warning
    */
    - return watchdog_thresh * (NSEC_PER_SEC / 5);
    + return get_softlockup_thresh() * (NSEC_PER_SEC / 5);
    }

    /* Commands for resetting the watchdog */
    @@ -182,7 +193,7 @@ static int is_softlockup(unsigned long touch_ts)
    unsigned long now = get_timestamp(smp_processor_id());

    /* Warn about unreasonable delays: */
    - if (time_after(now, touch_ts + watchdog_thresh))
    + if (time_after(now, touch_ts + get_softlockup_thresh()))
    return now - touch_ts;

    return 0;
    @@ -359,7 +370,7 @@ static int watchdog_nmi_enable(int cpu)

    /* Try to register using hardware perf events */
    wd_attr = &wd_hw_attr;
    - wd_attr->sample_period = hw_nmi_get_sample_period();
    + wd_attr->sample_period = hw_nmi_get_sample_period(watchdog_thresh);
    event = perf_event_create_kernel_counter(wd_attr, cpu, NULL, watchdog_overflow_callback);
    if (!IS_ERR(event)) {
    printk(KERN_INFO "NMI watchdog enabled, takes one hw-pmu counter.\n");
    --
    1.7.3.1


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