Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758873Ab2J2N2j (ORCPT ); Mon, 29 Oct 2012 09:28:39 -0400 Received: from mail-bk0-f46.google.com ([209.85.214.46]:42297 "EHLO mail-bk0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756758Ab2J2N2g (ORCPT ); Mon, 29 Oct 2012 09:28:36 -0400 From: Frederic Weisbecker To: LKML Cc: Frederic Weisbecker , Peter Zijlstra , Thomas Gleixner , Ingo Molnar , Andrew Morton , Steven Rostedt , Paul Gortmaker Subject: [RFC PATCH 7/9] irq_work: Make self-IPIs optable Date: Mon, 29 Oct 2012 14:28:14 +0100 Message-Id: <1351517296-9173-8-git-send-email-fweisbec@gmail.com> X-Mailer: git-send-email 1.7.5.4 In-Reply-To: <1351517296-9173-1-git-send-email-fweisbec@gmail.com> References: <1351517296-9173-1-git-send-email-fweisbec@gmail.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 6101 Lines: 204 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 Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: Ingo Molnar Cc: Andrew Morton Cc: Steven Rostedt Cc: Paul Gortmaker --- include/linux/irq_work.h | 31 ++++++++++++++++++++++++++ kernel/irq_work.c | 53 ++++++++++++++++++++++++++++++++------------- kernel/time/tick-sched.c | 3 +- 3 files changed, 70 insertions(+), 17 deletions(-) diff --git a/include/linux/irq_work.h b/include/linux/irq_work.h index b39ea0b..7b60c87 100644 --- a/include/linux/irq_work.h +++ b/include/linux/irq_work.h @@ -4,6 +4,20 @@ #include #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; @@ -17,8 +31,25 @@ void init_irq_work(struct irq_work *work, void (*func)(struct irq_work *)) work->func = func; } +#define DEFINE_IRQ_WORK(w, f) \ + struct irq_work w = { \ + .func = f, \ + } + +#define DEFINE_IRQ_WORK_LAZY(w, f) \ + struct irq_work w = { \ + .flags = IRQ_WORK_LAZY, \ + .func = f, \ + } + 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 d00011c..ce72b20 100644 --- a/kernel/irq_work.c +++ b/kernel/irq_work.c @@ -12,20 +12,10 @@ #include #include #include +#include +#include #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 static DEFINE_PER_CPU(struct llist_head, irq_work_list); @@ -66,10 +56,28 @@ static void __irq_work_queue(struct irq_work *work) preempt_disable(); empty = llist_add(&work->llnode, &__get_cpu_var(irq_work_list)); - /* The list was empty, raise self-interrupt to start processing. */ - if (empty) + + /* + * In any case, raise an IPI if requested and possible in case + * the queue is empty or it's filled with lazy works. + */ + if (!(work->flags & IRQ_WORK_LAZY) && arch_irq_work_has_ipi()) { arch_irq_work_raise(); + goto out; + } + if (empty) { + /* + * If the arch uses some other obscure way than IPI to raise + * an irq work, just raise and don't think further. + * Now if it can send an IPI, although not requested, and the tick + * is stopped, send it nonetheless otherwise we may wait a long while + * before that lazy work can run. + */ + if (!arch_irq_work_has_ipi() || tick_nohz_tick_stopped()) + arch_irq_work_raise(); + } +out: preempt_enable(); } @@ -93,12 +101,24 @@ 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; + + return true; +} + /* * Run the irq_work entries on this cpu. Requires to be ran from hardirq * context with local IRQs disabled. */ void irq_work_run(void) { + unsigned long flags; struct irq_work *work; struct llist_head *this_list; struct llist_node *llnode; @@ -120,13 +140,14 @@ void irq_work_run(void) * Clear the PENDING bit, after this point the @work * can be re-used. */ - work->flags = IRQ_WORK_BUSY; + flags = work->flags & ~IRQ_WORK_PENDING; + work->flags = flags; work->func(work); /* * Clear the BUSY bit and return to the free state if * no-one else claimed it meanwhile. */ - (void)cmpxchg(&work->flags, IRQ_WORK_BUSY, 0); + (void)cmpxchg(&work->flags, flags, flags & ~IRQ_WORK_BUSY); } } EXPORT_SYMBOL_GPL(irq_work_run); diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c index ccc1971..7ac2fd8 100644 --- a/kernel/time/tick-sched.c +++ b/kernel/time/tick-sched.c @@ -20,6 +20,7 @@ #include #include #include +#include #include @@ -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 { -- 1.7.5.4 -- 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/