Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757731AbaGSAog (ORCPT ); Fri, 18 Jul 2014 20:44:36 -0400 Received: from mail-wg0-f44.google.com ([74.125.82.44]:58623 "EHLO mail-wg0-f44.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754004AbaGSAo3 (ORCPT ); Fri, 18 Jul 2014 20:44:29 -0400 From: Frederic Weisbecker To: LKML Cc: Frederic Weisbecker , Ingo Molnar , "Paul E. McKenney" , Peter Zijlstra , Steven Rostedt , Thomas Gleixner , Viresh Kumar Subject: [PATCH 01/10] irq_work: Introduce void irq work Date: Sat, 19 Jul 2014 02:44:12 +0200 Message-Id: <1405730661-9355-2-git-send-email-fweisbec@gmail.com> X-Mailer: git-send-email 1.8.3.1 In-Reply-To: <1405730661-9355-1-git-send-email-fweisbec@gmail.com> References: <1405730661-9355-1-git-send-email-fweisbec@gmail.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Being able to trigger an empty IPI appears to be useless in the first place. Yet it is expected to be very useful for callers who just need to execute irq_enter() or irq_exit() to a remote target. More precisely this is going to be useful for the nohz subsystem which often needs a remote CPU to reschedule its tick when some state changed and require periodicity for any reason. Similar cases have been handled with random IPIs until now. But they surely bring unwanted overhead all along since they are all dedicated for specific tasks. Triggering an irq work/smp_call_function IPI should be enough to solve that. If competing and spurious IPIs become a problem, we can still optimize that later. Cc: Ingo Molnar Cc: Paul E. McKenney Cc: Peter Zijlstra Cc: Steven Rostedt Cc: Thomas Gleixner Cc: Viresh Kumar Signed-off-by: Frederic Weisbecker --- include/linux/irq_work.h | 1 + kernel/irq_work.c | 21 +++++++++++++++++++++ 2 files changed, 22 insertions(+) diff --git a/include/linux/irq_work.h b/include/linux/irq_work.h index bf9422c..b2ad065 100644 --- a/include/linux/irq_work.h +++ b/include/linux/irq_work.h @@ -36,6 +36,7 @@ bool irq_work_queue(struct irq_work *work); #ifdef CONFIG_SMP bool irq_work_queue_on(struct irq_work *work, int cpu); +void irq_work_void_on(int cpu); #endif void irq_work_run(void); diff --git a/kernel/irq_work.c b/kernel/irq_work.c index 4b0a890..36b7fb2 100644 --- a/kernel/irq_work.c +++ b/kernel/irq_work.c @@ -81,6 +81,27 @@ bool irq_work_queue_on(struct irq_work *work, int cpu) return true; } EXPORT_SYMBOL_GPL(irq_work_queue_on); + +/** + * irq_work_void_on(): Run a void IRQ on the target + * @cpu: The cpu to run the IRQ on + * + * Run a void IRQ for its own sake on the target. It's generally + * useful for callers which want to run irq_enter() or irq_exit() + * on a remote CPU. + */ +void irq_work_void_on(int cpu) +{ + /* + * NOTE: we could optimize that and spare some IPIs + * after checking that raised_list isn't empty before raising. + * This can't be done properly without cmpxchg() though so + * it may make things worse after all. But lets leave that + * possibility open in case people report such issue in the + * future. + */ + arch_send_call_function_single_ipi(cpu); +} #endif /* Enqueue the irq work @work on the current CPU */ -- 1.8.3.1 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/