On Wed, May 14, 2014 at 12:25:54AM +0200, Frederic Weisbecker wrote: > irq work currently only supports local callbacks. However its code > is mostly ready to run remote callbacks and we have some potential user. > > The full nohz subsystem currently open codes its own remote irq work > on top of the scheduler ipi when it wants a CPU to reevaluate its next > tick. However this ad hoc solution bloats the scheduler IPI. > > Lets just extend the irq work subsystem to support remote queuing on top > of the generic SMP IPI to handle this kind of user. This shouldn't add > noticeable overhead. > > Suggested-by: Peter Zijlstra <[email protected]> > Cc: Andrew Morton <[email protected]> > Cc: Ingo Molnar <[email protected]> > Cc: Kevin Hilman <[email protected]> > Cc: Paul E. McKenney <[email protected]> > Cc: Peter Zijlstra <[email protected]> > Cc: Thomas Gleixner <[email protected]> > Cc: Viresh Kumar <[email protected]> > Signed-off-by: Frederic Weisbecker <[email protected]> > --- > include/linux/irq_work.h | 2 ++ > kernel/irq_work.c | 19 ++++++++++++++++++- > kernel/smp.c | 4 ++++ > 3 files changed, 24 insertions(+), 1 deletion(-) > > diff --git a/include/linux/irq_work.h b/include/linux/irq_work.h > index 19ae05d..ae44aa2 100644 > --- a/include/linux/irq_work.h > +++ b/include/linux/irq_work.h > @@ -33,6 +33,8 @@ void init_irq_work(struct irq_work *work, void > (*func)(struct irq_work *)) > #define DEFINE_IRQ_WORK(name, _f) struct irq_work name = { .func = (_f), } > > bool irq_work_queue(struct irq_work *work); > +bool irq_work_queue_on(struct irq_work *work, int cpu); > + > void irq_work_run(void); > void irq_work_sync(struct irq_work *work); > > diff --git a/kernel/irq_work.c b/kernel/irq_work.c > index a82170e..9f9be55 100644 > --- a/kernel/irq_work.c > +++ b/kernel/irq_work.c > @@ -56,11 +56,28 @@ void __weak arch_irq_work_raise(void) > } > > /* > - * Enqueue the irq_work @entry unless it's already pending > + * 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) > +{ > + /* Only queue if not already pending */ > + if (!irq_work_claim(work)) > + return false; > + > + /* All work should have been flushed before going offline */ > + WARN_ON_ONCE(cpu_is_offline(cpu));
WARN_ON_ONCE(in_nmi());
> +
> + llist_add(&work->llnode, &per_cpu(irq_work_list, cpu));
> + native_send_call_func_single_ipi(cpu);
At the very leastestest make that:
if (llist_add(&work->llnode, &per_cpu(irq_work_list, cpu)))
native_send_call_func_single_ipi(cpu);
But ideally, also test the IRQ_WORK_LAZY support, its weird to have that
only be supported for the other queue.
Hmm, why do we need that LAZY crap, that completely wrecks a perfectly
simple thing.
The changelog (bc6679aef673f), not the printk() usage make much sense,
printk() can't cause an IPI storm... printk() isn't fast enough to storm
anything.
> +
> + return true;
> +}
> +EXPORT_SYMBOL_GPL(irq_work_queue_on);
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