Re: [PATCH 5/7] irq_work: Don't stop the tick with pending works

[Steven Rostedt <rostedt@goodmis.org>]

On Wed, 2012-11-14 at 21:37 +0100, Frederic Weisbecker wrote:
> 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 <fweisbec@gmail.com>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Ingo Molnar <mingo@kernel.org>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Steven Rostedt <rostedt@goodmis.org>
> Cc: Paul Gortmaker <paul.gortmaker@windriver.com>
> ---
>  include/linux/irq_work.h |    6 ++++++
>  kernel/irq_work.c        |   11 +++++++++++
>  kernel/time/tick-sched.c |    3 ++-
>  3 files changed, 19 insertions(+), 1 deletions(-)
> 
> diff --git a/include/linux/irq_work.h b/include/linux/irq_work.h
> index 6a9e8f5..a69704f 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 */
> diff --git a/kernel/irq_work.c b/kernel/irq_work.c
> index 64eddd5..b3c113a 100644
> --- a/kernel/irq_work.c
> +++ b/kernel/irq_work.c
> @@ -99,6 +99,17 @@ bool irq_work_queue(struct irq_work *work)
>  }
>  EXPORT_SYMBOL_GPL(irq_work_queue);
>  
> +bool irq_work_needs_cpu(void)
> +{
> +	struct llist_head *this_list;
> +
> +	this_list = &__get_cpu_var(irq_work_list);
> +	if (llist_empty(this_list))
> +		return false;
> +

I wounder if this should just be:

	return !llist_empty(&this_cpu_read(irq_work_list));

-- Steve


> +	return true;
> +}
> +
>  /*
>   * Run the irq_work entries on this cpu. Requires to be ran from hardirq
>   * context with local IRQs disabled.
> diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
> index 9e945aa..f249e8c 100644
> --- a/kernel/time/tick-sched.c
> +++ b/kernel/time/tick-sched.c
> @@ -20,6 +20,7 @@
>  #include <linux/profile.h>
>  #include <linux/sched.h>
>  #include <linux/module.h>
> +#include <linux/irq_work.h>
>  
>  #include <asm/irq_regs.h>
>  
> @@ -289,7 +290,7 @@ static ktime_t tick_nohz_stop_sched_tick(struct tick_sched *ts,
>  	} while (read_seqretry(&xtime_lock, seq));
>  
>  	if (rcu_needs_cpu(cpu, &rcu_delta_jiffies) || printk_needs_cpu(cpu) ||
> -	    arch_needs_cpu(cpu)) {
> +	    arch_needs_cpu(cpu) || irq_work_needs_cpu()) {
>  		next_jiffies = last_jiffies + 1;
>  		delta_jiffies = 1;
>  	} else {