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![Peter Zijlstra](/assets/img/avatar_default.png)
Currently irq_work_queue_on() will issue an unconditional arch_send_call_function_single_ipi() and has the handler do irq_work_run(). This is unfortunate in that it makes the IPI handler look at a second cacheline and it misses the opportunity to avoid the IPI. Instead note that struct irq_work and struct __call_single_data are very similar in layout, so use a few bits in the flags word to encode a type and stick the irq_work on the call_single_queue list. Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Signed-off-by: Ingo Molnar <mingo@kernel.org> Link: https://lore.kernel.org/r/20200526161908.011635912@infradead.org
204 lines
4.8 KiB
C
204 lines
4.8 KiB
C
// SPDX-License-Identifier: GPL-2.0-only
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/*
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* Copyright (C) 2010 Red Hat, Inc., Peter Zijlstra
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*
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* Provides a framework for enqueueing and running callbacks from hardirq
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* context. The enqueueing is NMI-safe.
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*/
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#include <linux/bug.h>
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#include <linux/kernel.h>
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#include <linux/export.h>
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#include <linux/irq_work.h>
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#include <linux/percpu.h>
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#include <linux/hardirq.h>
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#include <linux/irqflags.h>
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#include <linux/sched.h>
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#include <linux/tick.h>
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#include <linux/cpu.h>
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#include <linux/notifier.h>
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#include <linux/smp.h>
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#include <asm/processor.h>
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static DEFINE_PER_CPU(struct llist_head, raised_list);
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static DEFINE_PER_CPU(struct llist_head, lazy_list);
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/*
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* Claim the entry so that no one else will poke at it.
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*/
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static bool irq_work_claim(struct irq_work *work)
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{
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int oflags;
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oflags = atomic_fetch_or(IRQ_WORK_CLAIMED | CSD_TYPE_IRQ_WORK, &work->flags);
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/*
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* If the work is already pending, no need to raise the IPI.
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* The pairing atomic_fetch_andnot() in irq_work_run() makes sure
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* everything we did before is visible.
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*/
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if (oflags & IRQ_WORK_PENDING)
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return false;
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return true;
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}
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void __weak arch_irq_work_raise(void)
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{
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/*
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* Lame architectures will get the timer tick callback
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*/
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}
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/* Enqueue on current CPU, work must already be claimed and preempt disabled */
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static void __irq_work_queue_local(struct irq_work *work)
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{
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/* If the work is "lazy", handle it from next tick if any */
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if (atomic_read(&work->flags) & IRQ_WORK_LAZY) {
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if (llist_add(&work->llnode, this_cpu_ptr(&lazy_list)) &&
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tick_nohz_tick_stopped())
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arch_irq_work_raise();
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} else {
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if (llist_add(&work->llnode, this_cpu_ptr(&raised_list)))
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arch_irq_work_raise();
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}
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}
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/* Enqueue the irq work @work on the current CPU */
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bool irq_work_queue(struct irq_work *work)
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{
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/* Only queue if not already pending */
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if (!irq_work_claim(work))
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return false;
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/* Queue the entry and raise the IPI if needed. */
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preempt_disable();
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__irq_work_queue_local(work);
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preempt_enable();
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return true;
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}
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EXPORT_SYMBOL_GPL(irq_work_queue);
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/*
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* Enqueue the irq_work @work on @cpu unless it's already pending
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* somewhere.
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*
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* Can be re-enqueued while the callback is still in progress.
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*/
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bool irq_work_queue_on(struct irq_work *work, int cpu)
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{
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#ifndef CONFIG_SMP
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return irq_work_queue(work);
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#else /* CONFIG_SMP: */
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/* All work should have been flushed before going offline */
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WARN_ON_ONCE(cpu_is_offline(cpu));
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/* Only queue if not already pending */
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if (!irq_work_claim(work))
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return false;
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preempt_disable();
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if (cpu != smp_processor_id()) {
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/* Arch remote IPI send/receive backend aren't NMI safe */
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WARN_ON_ONCE(in_nmi());
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__smp_call_single_queue(cpu, &work->llnode);
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} else {
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__irq_work_queue_local(work);
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}
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preempt_enable();
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return true;
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#endif /* CONFIG_SMP */
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}
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bool irq_work_needs_cpu(void)
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{
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struct llist_head *raised, *lazy;
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raised = this_cpu_ptr(&raised_list);
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lazy = this_cpu_ptr(&lazy_list);
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if (llist_empty(raised) || arch_irq_work_has_interrupt())
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if (llist_empty(lazy))
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return false;
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/* All work should have been flushed before going offline */
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WARN_ON_ONCE(cpu_is_offline(smp_processor_id()));
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return true;
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}
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void irq_work_single(void *arg)
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{
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struct irq_work *work = arg;
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int flags;
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/*
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* Clear the PENDING bit, after this point the @work
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* can be re-used.
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* Make it immediately visible so that other CPUs trying
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* to claim that work don't rely on us to handle their data
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* while we are in the middle of the func.
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*/
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flags = atomic_fetch_andnot(IRQ_WORK_PENDING, &work->flags);
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lockdep_irq_work_enter(work);
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work->func(work);
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lockdep_irq_work_exit(work);
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/*
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* Clear the BUSY bit and return to the free state if
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* no-one else claimed it meanwhile.
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*/
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flags &= ~IRQ_WORK_PENDING;
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(void)atomic_cmpxchg(&work->flags, flags, flags & ~IRQ_WORK_BUSY);
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}
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static void irq_work_run_list(struct llist_head *list)
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{
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struct irq_work *work, *tmp;
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struct llist_node *llnode;
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BUG_ON(!irqs_disabled());
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if (llist_empty(list))
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return;
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llnode = llist_del_all(list);
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llist_for_each_entry_safe(work, tmp, llnode, llnode)
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irq_work_single(work);
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}
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/*
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* hotplug calls this through:
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* hotplug_cfd() -> flush_smp_call_function_queue()
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*/
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void irq_work_run(void)
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{
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irq_work_run_list(this_cpu_ptr(&raised_list));
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irq_work_run_list(this_cpu_ptr(&lazy_list));
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}
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EXPORT_SYMBOL_GPL(irq_work_run);
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void irq_work_tick(void)
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{
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struct llist_head *raised = this_cpu_ptr(&raised_list);
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if (!llist_empty(raised) && !arch_irq_work_has_interrupt())
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irq_work_run_list(raised);
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irq_work_run_list(this_cpu_ptr(&lazy_list));
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}
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/*
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* Synchronize against the irq_work @entry, ensures the entry is not
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* currently in use.
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*/
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void irq_work_sync(struct irq_work *work)
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{
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lockdep_assert_irqs_enabled();
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while (atomic_read(&work->flags) & IRQ_WORK_BUSY)
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cpu_relax();
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}
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EXPORT_SYMBOL_GPL(irq_work_sync);
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