Messages in this thread Patch in this message | | | From | Jan Kara <> | Subject | [PATCH 2/4] irq_work: Provide a irq work that can be processed on any cpu | Date | Thu, 7 Nov 2013 22:48:37 +0100 |
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Provide new irq work flag - IRQ_WORK_UNBOUND - meaning that can be processed on any cpu. This flag implies IRQ_WORK_LAZY so that things are simple and we don't have to pick any particular cpu to do the work. We just do the work from a timer tick on whichever cpu it happens first. This is useful as a lightweight and simple code path without locking or other dependencies to offload work to other cpu if possible.
We will use this type of irq work to make a guarantee of forward progress of printing to a (serial) console when printing on one cpu would cause interrupts to be disabled for too long.
Signed-off-by: Jan Kara <jack@suse.cz> --- include/linux/irq_work.h | 2 ++ kernel/irq_work.c | 41 +++++++++++++++++++++++++---------------- 2 files changed, 27 insertions(+), 16 deletions(-)
diff --git a/include/linux/irq_work.h b/include/linux/irq_work.h index 66017028dcb3..ca07a16355ed 100644 --- a/include/linux/irq_work.h +++ b/include/linux/irq_work.h @@ -16,6 +16,8 @@ #define IRQ_WORK_BUSY 2UL #define IRQ_WORK_FLAGS 3UL #define IRQ_WORK_LAZY 4UL /* Doesn't want IPI, wait for tick */ +#define __IRQ_WORK_UNBOUND 8UL /* Use IRQ_WORK_UNBOUND instead! */ +#define IRQ_WORK_UNBOUND (__IRQ_WORK_UNBOUND | IRQ_WORK_LAZY) /* Any cpu can process this work */ struct irq_work { unsigned long flags; diff --git a/kernel/irq_work.c b/kernel/irq_work.c index 55fcce6065cf..b06350b63c67 100644 --- a/kernel/irq_work.c +++ b/kernel/irq_work.c @@ -22,6 +22,9 @@ static DEFINE_PER_CPU(struct llist_head, irq_work_list); static DEFINE_PER_CPU(int, irq_work_raised); +/* List of irq-work any CPU can pick up */ +static LLIST_HEAD(unbound_irq_work_list); + /* * Claim the entry so that no one else will poke at it. */ @@ -70,12 +73,16 @@ void irq_work_queue(struct irq_work *work) /* Queue the entry and raise the IPI if needed. */ preempt_disable(); - llist_add(&work->llnode, &__get_cpu_var(irq_work_list)); + if (work->flags & __IRQ_WORK_UNBOUND) + llist_add(&work->llnode, &unbound_irq_work_list); + else + llist_add(&work->llnode, &__get_cpu_var(irq_work_list)); /* * If the work is not "lazy" or the tick is stopped, raise the irq * work interrupt (if supported by the arch), otherwise, just wait - * for the next tick. + * for the next tick. We do this even for unbound work to make sure + * *some* CPU will be doing the work. */ if (!(work->flags & IRQ_WORK_LAZY) || tick_nohz_tick_stopped()) { if (!this_cpu_cmpxchg(irq_work_raised, 0, 1)) @@ -100,28 +107,17 @@ bool irq_work_needs_cpu(void) return true; } -static void __irq_work_run(void) +static void process_irq_work_list(struct llist_head *llhead) { unsigned long flags; struct irq_work *work; - struct llist_head *this_list; struct llist_node *llnode; - - /* - * Reset the "raised" state right before we check the list because - * an NMI may enqueue after we find the list empty from the runner. - */ - __this_cpu_write(irq_work_raised, 0); - barrier(); - - this_list = &__get_cpu_var(irq_work_list); - if (llist_empty(this_list)) + if (llist_empty(llhead)) return; BUG_ON(!irqs_disabled()); - - llnode = llist_del_all(this_list); + llnode = llist_del_all(llhead); while (llnode != NULL) { work = llist_entry(llnode, struct irq_work, llnode); @@ -146,6 +142,19 @@ static void __irq_work_run(void) } } +static void __irq_work_run(void) +{ + /* + * Reset the "raised" state right before we check the list because + * an NMI may enqueue after we find the list empty from the runner. + */ + __this_cpu_write(irq_work_raised, 0); + barrier(); + + process_irq_work_list(&__get_cpu_var(irq_work_list)); + process_irq_work_list(&unbound_irq_work_list); +} + /* * Run the irq_work entries on this cpu. Requires to be ran from hardirq * context with local IRQs disabled. -- 1.8.1.4
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