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Date: Tue, 25 Aug 2009 11:50:39 -0300
From: Arnaldo Carvalho de Melo <acme@...hat.com>
To: Peter Zijlstra <peterz@...radead.org>
Cc: Ingo Molnar <mingo@...e.hu>, Thomas Gleixner <tglx@...utronix.de>,
linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [RFC][PATCH -rt] perf_counters: defer poll() wakeups to softirq
Em Tue, Aug 25, 2009 at 03:51:05PM +0200, Peter Zijlstra escreveu:
> Use timer softirq for wakeups on preempt_rt
>
> Normally pending work is work that cannot be done from NMI context, such
> as wakeups and disabling the counter. The pending work is a single
> linked list using atomic ops so that it functions from NMI context.
>
> Normally this is called from IRQ context through use of an self-IPI
> (x86) or upon enabling hard interrupts (powerpc). Architectures that do
> not implement perf_counter_set_pending() nor call
> perf_counter_do_pending() upon leaving NMI context will get a polling
> fallback from the timer softirq.
>
> However, in -rt we cannot do the wakeup from IRQ context because its a
> wait_queue wakup, which can be O(n), so defer all wakeups to the softirq
> fallback by creating a second pending list that's only processed from
> there.
>
> [ not tested at all... ]
Thanks a lot, no crashes, tons of samples collected, looks fine after:
[root@...1xm-2 ~]# uptime
09:49:48 up 38 min, 3 users, load average: 2.77, 18.72, 25.09
Will continue testing, but I guess I can give a:
Tested-by: Arnaldo Carvalho de Melo <acme@...hat.com>
> Signed-off-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
> ---
> include/linux/perf_counter.h | 5 +++
> kernel/perf_counter.c | 61 +++++++++++++++++++++++++++++++++--------
> kernel/timer.c | 2 +-
> 4 files changed, 65 insertions(+), 16 deletions(-)
>
> diff --git a/include/linux/perf_counter.h b/include/linux/perf_counter.h
> index 972f90d..e61eee1 100644
> --- a/include/linux/perf_counter.h
> +++ b/include/linux/perf_counter.h
> @@ -612,6 +612,9 @@ struct perf_counter {
> int pending_kill;
> int pending_disable;
> struct perf_pending_entry pending;
> +#ifdef CONFIG_PREEMPT_RT
> + struct perf_pending_entry pending_softirq;
> +#endif
>
> atomic_t event_limit;
>
> @@ -703,6 +706,7 @@ extern void perf_counter_exit_task(struct task_struct *child);
> extern void perf_counter_free_task(struct task_struct *task);
> extern void set_perf_counter_pending(void);
> extern void perf_counter_do_pending(void);
> +extern void perf_counter_do_pending_softirq(void);
> extern void perf_counter_print_debug(void);
> extern void __perf_disable(void);
> extern bool __perf_enable(void);
> @@ -787,6 +791,7 @@ static inline int perf_counter_init_task(struct task_struct *child) { return 0;
> static inline void perf_counter_exit_task(struct task_struct *child) { }
> static inline void perf_counter_free_task(struct task_struct *task) { }
> static inline void perf_counter_do_pending(void) { }
> +static inline void perf_counter_do_pending_softirq(void) { }
> static inline void perf_counter_print_debug(void) { }
> static inline void perf_disable(void) { }
> static inline void perf_enable(void) { }
> diff --git a/kernel/perf_counter.c b/kernel/perf_counter.c
> index 53abcbe..d3b065d 100644
> --- a/kernel/perf_counter.c
> +++ b/kernel/perf_counter.c
> @@ -2397,45 +2397,69 @@ static void perf_pending_counter(struct perf_pending_entry *entry)
> __perf_counter_disable(counter);
> }
>
> +#ifndef CONFIG_PREEMPT_RT
> if (counter->pending_wakeup) {
> counter->pending_wakeup = 0;
> perf_counter_wakeup(counter);
> }
> +#endif
> }
>
> +#ifdef CONFIG_PREEMPT_RT
> +static void perf_pending_counter_softirq(struct perf_pending_entry *entry)
> +{
> + struct perf_counter *counter = container_of(entry,
> + struct perf_counter, pending_softirq);
> +
> + if (counter->pending_wakeup) {
> + counter->pending_wakeup = 0;
> + perf_counter_wakeup(counter);
> + }
> +}
> +#endif
> +
> #define PENDING_TAIL ((struct perf_pending_entry *)-1UL)
>
> static DEFINE_PER_CPU(struct perf_pending_entry *, perf_pending_head) = {
> PENDING_TAIL,
> };
>
> -static void perf_pending_queue(struct perf_pending_entry *entry,
> - void (*func)(struct perf_pending_entry *))
> -{
> - struct perf_pending_entry **head;
> +static DEFINE_PER_CPU(struct perf_pending_entry *, perf_pending_softirq_head) = {
> + PENDING_TAIL,
> +};
>
> +static void __perf_pending_queue(struct perf_pending_entry **head,
> + struct perf_pending_entry *entry,
> + void (*func)(struct perf_pending_entry *))
> +{
> if (cmpxchg(&entry->next, NULL, PENDING_TAIL) != NULL)
> return;
>
> entry->func = func;
>
> - head = &get_cpu_var(perf_pending_head);
> -
> do {
> entry->next = *head;
> } while (cmpxchg(head, entry->next, entry) != entry->next);
> +}
>
> - set_perf_counter_pending();
> +static void perf_pending_queue(struct perf_pending_entry *entry,
> + void (*func)(struct perf_pending_entry *))
> +{
> + struct perf_pending_entry **head;
> +
> + head = &get_cpu_var(perf_pending_head);
> + __perf_pending_queue(head, entry, func);
> + put_cpu_var(perf_pending_head);
>
> - put_cpu_var(perf_pending_head);
> + set_perf_counter_pending();
> }
>
> -static int __perf_pending_run(void)
> +static int __perf_pending_run(struct perf_pending_entry **head)
> {
> struct perf_pending_entry *list;
> int nr = 0;
>
> - list = xchg(&__get_cpu_var(perf_pending_head), PENDING_TAIL);
> + list = xchg(head, PENDING_TAIL);
> while (list != PENDING_TAIL) {
> void (*func)(struct perf_pending_entry *);
> struct perf_pending_entry *entry = list;
> @@ -2465,7 +2489,8 @@ static inline int perf_not_pending(struct perf_counter *counter)
> * need to wait.
> */
> get_cpu();
> - __perf_pending_run();
> + __perf_pending_run(&__get_cpu_var(perf_pending_head));
> + __perf_pending_run(&__get_cpu_var(perf_pending_softirq_head));
> put_cpu();
>
> /*
> @@ -2483,7 +2508,13 @@ static void perf_pending_sync(struct perf_counter *counter)
>
> void perf_counter_do_pending(void)
> {
> - __perf_pending_run();
> + __perf_pending_run(&__get_cpu_var(perf_pending_head));
> +}
> +
> +void perf_counter_do_pending_softirq(void)
> +{
> + __perf_pending_run(&__get_cpu_var(perf_pending_head));
> + __perf_pending_run(&__get_cpu_var(perf_pending_softirq_head));
> }
>
> /*
> @@ -2543,8 +2574,14 @@ static void perf_output_wakeup(struct perf_output_handle *handle)
>
> if (handle->nmi) {
> handle->counter->pending_wakeup = 1;
> +#ifndef CONFIG_PREEMPT_RT
> perf_pending_queue(&handle->counter->pending,
> perf_pending_counter);
> +#else
> + __perf_pending_queue(&__get_cpu_var(perf_pending_softirq_head),
> + &handle->counter->pending_softirq,
> + perf_pending_counter_softirq);
> +#endif
> } else
> perf_counter_wakeup(handle->counter);
> }
> diff --git a/kernel/timer.c b/kernel/timer.c
> index 33fc9d1..1dd1456 100644
> --- a/kernel/timer.c
> +++ b/kernel/timer.c
> @@ -1188,7 +1188,7 @@ static void run_timer_softirq(struct softirq_action *h)
> {
> struct tvec_base *base = __get_cpu_var(tvec_bases);
>
> - perf_counter_do_pending();
> + perf_counter_do_pending_softirq();
>
> hrtimer_run_pending();
>
--
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