From 33a5f6261a61af28f7b4c86f9f958da0f206c914 Mon Sep 17 00:00:00 2001 From: Frederic Weisbecker Date: Thu, 11 Oct 2012 17:52:56 +0200 Subject: nohz: Add API to check tick state We need some quick way to check if the CPU has stopped its tick. This will be useful to implement the printk tick using the irq work subsystem. Signed-off-by: Frederic Weisbecker Acked-by: Steven Rostedt Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: Ingo Molnar Cc: Andrew Morton Cc: Paul Gortmaker --- include/linux/tick.h | 17 ++++++++++++++++- 1 file changed, 16 insertions(+), 1 deletion(-) (limited to 'include/linux') diff --git a/include/linux/tick.h b/include/linux/tick.h index f37fceb69b73..2307dd31b966 100644 --- a/include/linux/tick.h +++ b/include/linux/tick.h @@ -8,6 +8,8 @@ #include #include +#include +#include #ifdef CONFIG_GENERIC_CLOCKEVENTS @@ -122,13 +124,26 @@ static inline int tick_oneshot_mode_active(void) { return 0; } #endif /* !CONFIG_GENERIC_CLOCKEVENTS */ # ifdef CONFIG_NO_HZ +DECLARE_PER_CPU(struct tick_sched, tick_cpu_sched); + +static inline int tick_nohz_tick_stopped(void) +{ + return __this_cpu_read(tick_cpu_sched.tick_stopped); +} + extern void tick_nohz_idle_enter(void); extern void tick_nohz_idle_exit(void); extern void tick_nohz_irq_exit(void); extern ktime_t tick_nohz_get_sleep_length(void); extern u64 get_cpu_idle_time_us(int cpu, u64 *last_update_time); extern u64 get_cpu_iowait_time_us(int cpu, u64 *last_update_time); -# else + +# else /* !CONFIG_NO_HZ */ +static inline int tick_nohz_tick_stopped(void) +{ + return 0; +} + static inline void tick_nohz_idle_enter(void) { } static inline void tick_nohz_idle_exit(void) { } -- cgit v1.2.3 From 00b42959106a9ca1c2899e591ae4e9a83ad6af05 Mon Sep 17 00:00:00 2001 From: Frederic Weisbecker Date: Wed, 7 Nov 2012 21:03:07 +0100 Subject: irq_work: Don't stop the tick with pending works Don't stop the tick if we have pending irq works on the queue, otherwise if the arch can't raise self-IPIs, we may not find an opportunity to execute the pending works for a while. Signed-off-by: Frederic Weisbecker Acked-by: Steven Rostedt Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: Ingo Molnar Cc: Andrew Morton Cc: Paul Gortmaker --- include/linux/irq_work.h | 6 ++++++ 1 file changed, 6 insertions(+) (limited to 'include/linux') diff --git a/include/linux/irq_work.h b/include/linux/irq_work.h index 6a9e8f5399e2..a69704f37204 100644 --- a/include/linux/irq_work.h +++ b/include/linux/irq_work.h @@ -20,4 +20,10 @@ bool irq_work_queue(struct irq_work *work); void irq_work_run(void); void irq_work_sync(struct irq_work *work); +#ifdef CONFIG_IRQ_WORK +bool irq_work_needs_cpu(void); +#else +static bool irq_work_needs_cpu(void) { return false; } +#endif + #endif /* _LINUX_IRQ_WORK_H */ -- cgit v1.2.3 From bc6679aef673f9dcb8f718528fc3df49ff661af9 Mon Sep 17 00:00:00 2001 From: Frederic Weisbecker Date: Fri, 19 Oct 2012 16:43:41 -0400 Subject: irq_work: Make self-IPIs optable On irq work initialization, let the user choose to define it as "lazy" or not. "Lazy" means that we don't want to send an IPI (provided the arch can anyway) when we enqueue this work but we rather prefer to wait for the next timer tick to execute our work if possible. This is going to be a benefit for non-urgent enqueuers (like printk in the future) that may prefer not to raise an IPI storm in case of frequent enqueuing on short periods of time. Signed-off-by: Frederic Weisbecker Acked-by: Steven Rostedt Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: Ingo Molnar Cc: Andrew Morton Cc: Paul Gortmaker --- include/linux/irq_work.h | 14 ++++++++++++++ 1 file changed, 14 insertions(+) (limited to 'include/linux') diff --git a/include/linux/irq_work.h b/include/linux/irq_work.h index a69704f37204..b28eb60c8bf6 100644 --- a/include/linux/irq_work.h +++ b/include/linux/irq_work.h @@ -3,6 +3,20 @@ #include +/* + * An entry can be in one of four states: + * + * free NULL, 0 -> {claimed} : free to be used + * claimed NULL, 3 -> {pending} : claimed to be enqueued + * pending next, 3 -> {busy} : queued, pending callback + * busy NULL, 2 -> {free, claimed} : callback in progress, can be claimed + */ + +#define IRQ_WORK_PENDING 1UL +#define IRQ_WORK_BUSY 2UL +#define IRQ_WORK_FLAGS 3UL +#define IRQ_WORK_LAZY 4UL /* Doesn't want IPI, wait for tick */ + struct irq_work { unsigned long flags; struct llist_node llnode; -- cgit v1.2.3 From 74876a98a87a115254b3a66a14b27320b7f0acaa Mon Sep 17 00:00:00 2001 From: Frederic Weisbecker Date: Fri, 12 Oct 2012 18:00:23 +0200 Subject: printk: Wake up klogd using irq_work klogd is woken up asynchronously from the tick in order to do it safely. However if printk is called when the tick is stopped, the reader won't be woken up until the next interrupt, which might not fire for a while. As a result, the user may miss some message. To fix this, lets implement the printk tick using a lazy irq work. This subsystem takes care of the timer tick state and can fix up accordingly. Signed-off-by: Frederic Weisbecker Acked-by: Steven Rostedt Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: Ingo Molnar Cc: Andrew Morton Cc: Paul Gortmaker --- include/linux/printk.h | 3 --- 1 file changed, 3 deletions(-) (limited to 'include/linux') diff --git a/include/linux/printk.h b/include/linux/printk.h index 9afc01e5a0a6..86c4b6294713 100644 --- a/include/linux/printk.h +++ b/include/linux/printk.h @@ -98,9 +98,6 @@ int no_printk(const char *fmt, ...) extern asmlinkage __printf(1, 2) void early_printk(const char *fmt, ...); -extern int printk_needs_cpu(int cpu); -extern void printk_tick(void); - #ifdef CONFIG_PRINTK asmlinkage __printf(5, 0) int vprintk_emit(int facility, int level, -- cgit v1.2.3