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Date: Thu, 12 Feb 2009 21:27:08 -0800
From: Tim Hockin <thockin@...gle.com>
To: Andi Kleen <andi@...stfloor.org>
Cc: akpm@...ux-foundation.org, x86@...stfloor.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH] [4/10] x86: MCE: Switch machine check polling to per CPU
timer v3
On Thu, Feb 12, 2009 at 4:37 AM, Andi Kleen <andi@...stfloor.org> wrote:
>
> Impact: Higher priority bug fix
>
> The machine check poller runs a single timer and then broadcasted an
> IPI to all CPUs to check them. This leads to unnecessary
> synchronization between CPUs. The original CPU running the timer has
> to wait potentially a long time for all other CPUs answering. This is
> also real time unfriendly and in general inefficient.
>
> This was especially a problem on systems with a lot of events where
> the poller run with a higher frequency after processing some events.
> There could be more and more CPU time wasted with this, to
> the point of significantly slowing down machines.
>
> The machine check polling is actually fully independent per CPU, so
> there's no reason to not just do this all with per CPU timers. This
> patch implements that.
Great! W're going to patch this is an sanity check it here. We'll
send you info when we have some results. It looks good to me.
> Also switch the poller also to use standard timers instead of work
> queues. It was using work queues to be able to execute a user program
> on a event, but mce_notify_user() handles this case now with a
> separate callback. So instead always run the poll code in in a
> standard per CPU timer, which means that in the common case of not
> having to execute a trigger there will be less overhead.
>
> This allows to clean up the initialization significantly, because
> standard timers are already up when machine checks get init'ed. No
> multiple initialization functions.
>
> Thanks to Thomas Gleixner for some help.
>
> Cc: thockin@...gle.com
> v2: Use del_timer_sync() on cpu shutdown and don't try to handle
> migrated timers.
> v3: Add WARN_ON for timer running on unexpected CPU
>
> Signed-off-by: Andi Kleen <ak@...ux.intel.com>
>
> ---
> arch/x86/kernel/cpu/mcheck/mce_64.c | 68 +++++++++++++++++++++++-------------
> 1 file changed, 45 insertions(+), 23 deletions(-)
>
> Index: linux/arch/x86/kernel/cpu/mcheck/mce_64.c
> ===================================================================
> --- linux.orig/arch/x86/kernel/cpu/mcheck/mce_64.c 2009-02-12 11:30:51.000000000 +0100
> +++ linux/arch/x86/kernel/cpu/mcheck/mce_64.c 2009-02-12 12:10:21.000000000 +0100
> @@ -353,18 +353,17 @@
>
> static int check_interval = 5 * 60; /* 5 minutes */
> static int next_interval; /* in jiffies */
> -static void mcheck_timer(struct work_struct *work);
> -static DECLARE_DELAYED_WORK(mcheck_work, mcheck_timer);
> +static void mcheck_timer(unsigned long);
> +static DEFINE_PER_CPU(struct timer_list, mce_timer);
>
> -static void mcheck_check_cpu(void *info)
> +static void mcheck_timer(unsigned long data)
> {
> + struct timer_list *t = &per_cpu(mce_timer, data);
> +
> + WARN_ON(smp_processor_id() != data);
> +
> if (mce_available(¤t_cpu_data))
> do_machine_check(NULL, 0);
> -}
> -
> -static void mcheck_timer(struct work_struct *work)
> -{
> - on_each_cpu(mcheck_check_cpu, NULL, 1);
>
> /*
> * Alert userspace if needed. If we logged an MCE, reduce the
> @@ -377,7 +376,8 @@
> (int)round_jiffies_relative(check_interval*HZ));
> }
>
> - schedule_delayed_work(&mcheck_work, next_interval);
> + t->expires = jiffies + next_interval;
> + add_timer(t);
> }
>
> static void mce_do_trigger(struct work_struct *work)
> @@ -436,16 +436,11 @@
>
> static __init int periodic_mcheck_init(void)
> {
> - next_interval = check_interval * HZ;
> - if (next_interval)
> - schedule_delayed_work(&mcheck_work,
> - round_jiffies_relative(next_interval));
> - idle_notifier_register(&mce_idle_notifier);
> - return 0;
> + idle_notifier_register(&mce_idle_notifier);
> + return 0;
> }
> __initcall(periodic_mcheck_init);
>
> -
> /*
> * Initialize Machine Checks for a CPU.
> */
> @@ -515,6 +510,20 @@
> }
> }
>
> +static void mce_init_timer(void)
> +{
> + struct timer_list *t = &__get_cpu_var(mce_timer);
> +
> + /* data race harmless because everyone sets to the same value */
> + if (!next_interval)
> + next_interval = check_interval * HZ;
> + if (!next_interval)
> + return;
> + setup_timer(t, mcheck_timer, smp_processor_id());
> + t->expires = round_jiffies_relative(jiffies + next_interval);
> + add_timer(t);
> +}
> +
> /*
> * Called for each booted CPU to set up machine checks.
> * Must be called with preempt off.
> @@ -529,6 +538,7 @@
>
> mce_init(NULL);
> mce_cpu_features(c);
> + mce_init_timer();
> }
>
> /*
> @@ -735,17 +745,19 @@
> return 0;
> }
>
> +static void mce_cpu_restart(void *data)
> +{
> + del_timer_sync(&__get_cpu_var(mce_timer));
> + if (mce_available(¤t_cpu_data))
> + mce_init(NULL);
> + mce_init_timer();
> +}
> +
> /* Reinit MCEs after user configuration changes */
> static void mce_restart(void)
> {
> - if (next_interval)
> - cancel_delayed_work(&mcheck_work);
> - /* Timer race is harmless here */
> - on_each_cpu(mce_init, NULL, 1);
> next_interval = check_interval * HZ;
> - if (next_interval)
> - schedule_delayed_work(&mcheck_work,
> - round_jiffies_relative(next_interval));
> + on_each_cpu(mce_cpu_restart, NULL, 1);
> }
>
> static struct sysdev_class mce_sysclass = {
> @@ -874,6 +886,7 @@
> unsigned long action, void *hcpu)
> {
> unsigned int cpu = (unsigned long)hcpu;
> + struct timer_list *t = &per_cpu(mce_timer, cpu);
>
> switch (action) {
> case CPU_ONLINE:
> @@ -888,6 +901,15 @@
> threshold_cpu_callback(action, cpu);
> mce_remove_device(cpu);
> break;
> + case CPU_DOWN_PREPARE:
> + case CPU_DOWN_PREPARE_FROZEN:
> + del_timer_sync(t);
> + break;
> + case CPU_DOWN_FAILED:
> + case CPU_DOWN_FAILED_FROZEN:
> + t->expires = round_jiffies_relative(jiffies + next_interval);
> + add_timer_on(t, cpu);
> + break;
> }
> return NOTIFY_OK;
> }
>
--
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