Re: [PATCH] [1/4] x86: MCE: Make polling timer interval per CPU

Hidetoshi Seto
2009-04-08T03:44:20Z

Andi Kleen wrote:
> Impact: bug fix
>
> The polling timer while running per CPU still uses a global next_interval
> variable, which lead to some CPUs either polling too fast or too slow.
> This was not a serious problem because all errors get picked up eventually,
> but it's still better to avoid it. Turn next_interval into a per cpu variable.
>
> Signed-off-by: Andi Kleen <ak@linux.intel.com>
>
> ---
> arch/x86/kernel/cpu/mcheck/mce_64.c | 25 +++++++++++++------------
> 1 file changed, 13 insertions(+), 12 deletions(-)
>
> Index: linux/arch/x86/kernel/cpu/mcheck/mce_64.c
> ===================================================================
> --- linux.orig/arch/x86/kernel/cpu/mcheck/mce_64.c 2009-04-07 16:09:57.000000000 +0200
> +++ linux/arch/x86/kernel/cpu/mcheck/mce_64.c 2009-04-07 16:43:16.000000000 +0200
> @@ -452,13 +452,14 @@
> */
>
> static int check_interval = 5 * 60; /* 5 minutes */
> -static int next_interval; /* in jiffies */
> +static DEFINE_PER_CPU(int, next_interval); /* in jiffies */
> static void mcheck_timer(unsigned long);
> static DEFINE_PER_CPU(struct timer_list, mce_timer);
>
> static void mcheck_timer(unsigned long data)
> {
> struct timer_list *t = &per_cpu(mce_timer, data);
> + int *n;
>
> WARN_ON(smp_processor_id() != data);
>
> @@ -470,14 +471,14 @@
> * Alert userspace if needed. If we logged an MCE, reduce the
> * polling interval, otherwise increase the polling interval.
> */
> + n = &__get_cpu_var(next_interval);
> if (mce_notify_user()) {
> - next_interval = max(next_interval/2, HZ/100);
> + *n = max(*n/2, HZ/100);
> } else {
> - next_interval = min(next_interval * 2,
> - (int)round_jiffies_relative(check_interval*HZ));
> + *n = min(*n*2, (int)round_jiffies_relative(check_interval*HZ));
> }
>
> - t->expires = jiffies + next_interval;
> + t->expires = jiffies + *n;
> add_timer(t);
> }
>
> @@ -632,14 +633,14 @@
> static void mce_init_timer(void)
> {
> struct timer_list *t = &__get_cpu_var(mce_timer);
> + int *n = &__get_cpu_var(next_interval);
>
> - /* data race harmless because everyone sets to the same value */
> - if (!next_interval)
> - next_interval = check_interval * HZ;
> - if (!next_interval)

[plan A]
Add
if (!check_interval)
return;

Or...

> + if (!*n)
> + *n = check_interval * HZ;
> + if (!*n)
> return;
> setup_timer(t, mcheck_timer, smp_processor_id());
> - t->expires = round_jiffies(jiffies + next_interval);
> + t->expires = round_jiffies(jiffies + *n);
> add_timer(t);
> }
>
> @@ -907,7 +908,6 @@
> /* Reinit MCEs after user configuration changes */
> static void mce_restart(void)
> {
> - next_interval = check_interval * HZ;
> on_each_cpu(mce_cpu_restart, NULL, 1);
> }
>

[plan B]
Don't remove this line.

Take A or B, or we cannot stop polling timer by setting check_interval
to 0 via sysfs and then the timer will spin with 0 interval.

Thanks,
H.Seto

> @@ -1110,7 +1110,8 @@
> break;
> case CPU_DOWN_FAILED:
> case CPU_DOWN_FAILED_FROZEN:
> - t->expires = round_jiffies(jiffies + next_interval);
> + t->expires = round_jiffies(jiffies +
> + __get_cpu_var(next_interval));
> add_timer_on(t, cpu);
> smp_call_function_single(cpu, mce_reenable_cpu, &action, 1);
> break;
> --
> To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at http://vger.kernel.org/majordomo-info.html
> Please read the FAQ at http://www.tux.org/lkml/
>