+ fweisbec, who did the remote bits
On Sat, Mar 30, 2019 at 01:10:28PM +1000, Nicholas Piggin wrote:
> Something like this?
>
> kernel/irq_work: Do not raise an IPI when queueing work on the local CPU
>
> The QEMU powerpc/pseries machine model was not expecting a self-IPI,
> and it may be a bit surprising thing to do, so have irq_work_queue_on
> do local queueing when target is current CPU.
This seems OK to me.
> Suggested-by: Steven Rostedt <rost...@goodmis.org>
> Signed-off-by: Nicholas Piggin <npig...@gmail.com>
Acked-by: Peter Zijlstra (Intel) <pet...@infradead.org>
> ---
> kernel/irq_work.c | 78 ++++++++++++++++++++++++++---------------------
> 1 file changed, 43 insertions(+), 35 deletions(-)
>
> diff --git a/kernel/irq_work.c b/kernel/irq_work.c
> index 6b7cdf17ccf8..f0e539d0f879 100644
> --- a/kernel/irq_work.c
> +++ b/kernel/irq_work.c
> @@ -56,61 +56,69 @@ void __weak arch_irq_work_raise(void)
> */
> }
>
> -/*
> - * Enqueue the irq_work @work on @cpu unless it's already pending
> - * somewhere.
> - *
> - * Can be re-enqueued while the callback is still in progress.
> - */
> -bool irq_work_queue_on(struct irq_work *work, int cpu)
> +/* Enqueue on current CPU, work must already be claimed and preempt disabled
> */
> +static void __irq_work_queue(struct irq_work *work)
> {
> - /* All work should have been flushed before going offline */
> - WARN_ON_ONCE(cpu_is_offline(cpu));
> -
> -#ifdef CONFIG_SMP
> -
> - /* Arch remote IPI send/receive backend aren't NMI safe */
> - WARN_ON_ONCE(in_nmi());
> + /* If the work is "lazy", handle it from next tick if any */
> + if (work->flags & IRQ_WORK_LAZY) {
> + if (llist_add(&work->llnode, this_cpu_ptr(&lazy_list)) &&
> + tick_nohz_tick_stopped())
> + arch_irq_work_raise();
> + } else {
> + if (llist_add(&work->llnode, this_cpu_ptr(&raised_list)))
> + arch_irq_work_raise();
> + }
> +}
>
> +/* Enqueue the irq work @work on the current CPU */
> +bool irq_work_queue(struct irq_work *work)
> +{
> /* Only queue if not already pending */
> if (!irq_work_claim(work))
> return false;
>
> - if (llist_add(&work->llnode, &per_cpu(raised_list, cpu)))
> - arch_send_call_function_single_ipi(cpu);
> -
> -#else /* #ifdef CONFIG_SMP */
> - irq_work_queue(work);
> -#endif /* #else #ifdef CONFIG_SMP */
> + /* Queue the entry and raise the IPI if needed. */
> + preempt_disable();
> + __irq_work_queue(work);
> + preempt_enable();
>
> return true;
> }
> +EXPORT_SYMBOL_GPL(irq_work_queue);
>
> -/* Enqueue the irq work @work on the current CPU */
> -bool irq_work_queue(struct irq_work *work)
> +/*
> + * Enqueue the irq_work @work on @cpu unless it's already pending
> + * somewhere.
> + *
> + * Can be re-enqueued while the callback is still in progress.
> + */
> +bool irq_work_queue_on(struct irq_work *work, int cpu)
> {
> +#ifndef CONFIG_SMP
> + return irq_work_queue(work);
> +
> +#else /* #ifndef CONFIG_SMP */
> + /* All work should have been flushed before going offline */
> + WARN_ON_ONCE(cpu_is_offline(cpu));
> +
> /* Only queue if not already pending */
> if (!irq_work_claim(work))
> return false;
>
> - /* Queue the entry and raise the IPI if needed. */
> preempt_disable();
> -
> - /* If the work is "lazy", handle it from next tick if any */
> - if (work->flags & IRQ_WORK_LAZY) {
> - if (llist_add(&work->llnode, this_cpu_ptr(&lazy_list)) &&
> - tick_nohz_tick_stopped())
> - arch_irq_work_raise();
> - } else {
> - if (llist_add(&work->llnode, this_cpu_ptr(&raised_list)))
> - arch_irq_work_raise();
> - }
> -
> + if (cpu != smp_processor_id()) {
> + /* Arch remote IPI send/receive backend aren't NMI safe */
> + WARN_ON_ONCE(in_nmi());
> + if (llist_add(&work->llnode, &per_cpu(raised_list, cpu)))
> + arch_send_call_function_single_ipi(cpu);
> + } else
> + __irq_work_queue(work);
> preempt_enable();
>
> return true;
> +#endif /* #else #ifndef CONFIG_SMP */
> }
> -EXPORT_SYMBOL_GPL(irq_work_queue);
> +
>
> bool irq_work_needs_cpu(void)
> {
> --
> 2.20.1
>
