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    SubjectRe: [patch 1/2] x86: mce Cleanup timer mess
    Hi, Tony and Thomas

    This patch has been merged, but It still have some confusion, please
    see inline comment and give me some explanation.

    于 2012/5/25 1:54, Thomas Gleixner 写道:
    > Use unsigned long for dealing with jiffies not int. Rename the
    > callback to something sensible. Use __this_cpu_read/write for
    > accessing per cpu data.
    >
    > Signed-off-by: Thomas Gleixner <tglx@linutronix.de> ---
    > arch/x86/kernel/cpu/mcheck/mce.c | 31
    > ++++++++++++++++--------------- 1 file changed, 16 insertions(+),
    > 15 deletions(-)
    >
    > Index: linux-2.6/arch/x86/kernel/cpu/mcheck/mce.c
    > ===================================================================
    >
    >
    >
    --- linux-2.6.orig/arch/x86/kernel/cpu/mcheck/mce.c
    > +++ linux-2.6/arch/x86/kernel/cpu/mcheck/mce.c @@ -1237,15
    > +1237,15 @@ void mce_log_therm_throt_event(__u64 sta * poller finds
    > an MCE, poll 2x faster. When the poller finds no more * errors,
    > poll 2x slower (up to check_interval seconds). */ -static int
    > check_interval = 5 * 60; /* 5 minutes */ +static unsigned long
    > check_interval = 5 * 60; /* 5 minutes */
    >
    > -static DEFINE_PER_CPU(int, mce_next_interval); /* in jiffies */
    > +static DEFINE_PER_CPU(unsigned long, mce_next_interval); /* in
    > jiffies */ static DEFINE_PER_CPU(struct timer_list, mce_timer);
    >
    > -static void mce_start_timer(unsigned long data) +static void
    > mce_timer_fn(unsigned long data) { - struct timer_list *t =
    > &per_cpu(mce_timer, data); - int *n; + struct timer_list *t =
    > &__get_cpu_var(mce_timer); + unsigned long iv;
    >
    > WARN_ON(smp_processor_id() != data);
    >
    > @@ -1258,13 +1258,14 @@ static void mce_start_timer(unsigned lon *
    > Alert userspace if needed. If we logged an MCE, reduce the *
    > polling interval, otherwise increase the polling interval. */ - n
    > = &__get_cpu_var(mce_next_interval); + iv =
    > __this_cpu_read(mce_next_interval); if (mce_notify_irq()) - *n =
    > max(*n/2, HZ/100); + iv = max(iv, (unsigned long) HZ/100);

    Here Thomas changed original mode from "*n = max(*n/2, HZ/100);"
    to "iv = max(iv, (unsigned long) HZ/100);", which means *iv* will not
    be decremented but only incremented in _else_ branch. If so, eventually
    the *iv will be equal to *check_interval*. I don't think it makes sense.
    Even we use new logic, the comment before these codes should be updated.

    So Thomas, would you please explain why you use this new logic?

    > else - *n = min(*n*2,
    > (int)round_jiffies_relative(check_interval*HZ)); + iv = min(iv *
    > 2, round_jiffies_relative(check_interval * HZ)); +
    > __this_cpu_write(mce_next_interval, iv);
    >
    > - t->expires = jiffies + *n; + t->expires = jiffies + iv;
    > add_timer_on(t, smp_processor_id()); }
    >
    > @@ -1542,17 +1543,17 @@ static void __mcheck_cpu_init_vendor(str
    > static void __mcheck_cpu_init_timer(void) { struct timer_list *t =
    > &__get_cpu_var(mce_timer); - int *n =
    > &__get_cpu_var(mce_next_interval); + unsigned long iv =
    > __this_cpu_read(mce_next_interval);
    >
    > - setup_timer(t, mce_start_timer, smp_processor_id()); +
    > setup_timer(t, mce_timer_fn, smp_processor_id());
    >
    > if (mce_ignore_ce) return;
    >
    > - *n = check_interval * HZ; - if (!*n) +
    > __this_cpu_write(mce_next_interval, iv); + if (!iv) return; -
    > t->expires = round_jiffies(jiffies + *n); + t->expires =
    > round_jiffies(jiffies + iv); add_timer_on(t, smp_processor_id());
    > }
    >
    > @@ -2262,7 +2263,7 @@ mce_cpu_callback(struct notifier_block *
    > case CPU_DOWN_FAILED_FROZEN: if (!mce_ignore_ce && check_interval)
    > { t->expires = round_jiffies(jiffies + -
    > __get_cpu_var(mce_next_interval)); +
    > per_cpu(mce_next_interval, cpu)); add_timer_on(t, cpu); }
    > smp_call_function_single(cpu, mce_reenable_cpu, &action, 1);
    >
    >
    >

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