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    Subject[PATCH -v10 3/4] irq_work, Use llist in irq_work
    Date
    Use llist in irq_work instead of the lock-less linked list
    implementation in irq_work to avoid the code duplication.

    Signed-off-by: Huang Ying <ying.huang@intel.com>
    Cc: Peter Zijlstra <peterz@infradead.org>
    ---
    include/linux/irq_work.h | 15 ++++---
    init/Kconfig | 1
    kernel/irq_work.c | 92 ++++++++++++++++++-----------------------------
    3 files changed, 47 insertions(+), 61 deletions(-)

    --- a/include/linux/irq_work.h
    +++ b/include/linux/irq_work.h
    @@ -1,20 +1,23 @@
    #ifndef _LINUX_IRQ_WORK_H
    #define _LINUX_IRQ_WORK_H

    +#include <linux/llist.h>
    +
    struct irq_work {
    - struct irq_work *next;
    + unsigned long flags;
    + struct llist_node llnode;
    void (*func)(struct irq_work *);
    };

    static inline
    -void init_irq_work(struct irq_work *entry, void (*func)(struct irq_work *))
    +void init_irq_work(struct irq_work *work, void (*func)(struct irq_work *))
    {
    - entry->next = NULL;
    - entry->func = func;
    + work->flags = 0;
    + work->func = func;
    }

    -bool irq_work_queue(struct irq_work *entry);
    +bool irq_work_queue(struct irq_work *work);
    void irq_work_run(void);
    -void irq_work_sync(struct irq_work *entry);
    +void irq_work_sync(struct irq_work *work);

    #endif /* _LINUX_IRQ_WORK_H */
    --- a/init/Kconfig
    +++ b/init/Kconfig
    @@ -27,6 +27,7 @@ config HAVE_IRQ_WORK
    config IRQ_WORK
    bool
    depends on HAVE_IRQ_WORK
    + select LLIST

    menu "General setup"

    --- a/kernel/irq_work.c
    +++ b/kernel/irq_work.c
    @@ -17,49 +17,34 @@
    * 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
    - *
    - * We use the lower two bits of the next pointer to keep PENDING and BUSY
    - * flags.
    */

    #define IRQ_WORK_PENDING 1UL
    #define IRQ_WORK_BUSY 2UL
    #define IRQ_WORK_FLAGS 3UL

    -static inline bool irq_work_is_set(struct irq_work *entry, int flags)
    -{
    - return (unsigned long)entry->next & flags;
    -}
    -
    -static inline struct irq_work *irq_work_next(struct irq_work *entry)
    -{
    - unsigned long next = (unsigned long)entry->next;
    - next &= ~IRQ_WORK_FLAGS;
    - return (struct irq_work *)next;
    -}
    +#define LIST_NONEMPTY_BIT 0

    -static inline struct irq_work *next_flags(struct irq_work *entry, int flags)
    -{
    - unsigned long next = (unsigned long)entry;
    - next |= flags;
    - return (struct irq_work *)next;
    -}
    +struct irq_work_list {
    + unsigned long flags;
    + struct llist_head llist;
    +};

    -static DEFINE_PER_CPU(struct irq_work *, irq_work_list);
    +static DEFINE_PER_CPU(struct irq_work_list, irq_work_lists);

    /*
    * Claim the entry so that no one else will poke at it.
    */
    -static bool irq_work_claim(struct irq_work *entry)
    +static bool irq_work_claim(struct irq_work *work)
    {
    - struct irq_work *next, *nflags;
    + unsigned long flags, nflags;

    do {
    - next = entry->next;
    - if ((unsigned long)next & IRQ_WORK_PENDING)
    + flags = work->flags;
    + if (flags & IRQ_WORK_PENDING)
    return false;
    - nflags = next_flags(next, IRQ_WORK_FLAGS);
    - } while (cmpxchg(&entry->next, next, nflags) != next);
    + nflags = flags | IRQ_WORK_FLAGS;
    + } while (cmpxchg(&work->flags, flags, nflags) != flags);

    return true;
    }
    @@ -75,23 +60,19 @@ void __weak arch_irq_work_raise(void)
    /*
    * Queue the entry and raise the IPI if needed.
    */
    -static void __irq_work_queue(struct irq_work *entry)
    +static void __irq_work_queue(struct irq_work *work)
    {
    - struct irq_work *next;
    + struct irq_work_list *irq_work_list;

    - preempt_disable();
    + irq_work_list = &get_cpu_var(irq_work_lists);

    - do {
    - next = __this_cpu_read(irq_work_list);
    - /* Can assign non-atomic because we keep the flags set. */
    - entry->next = next_flags(next, IRQ_WORK_FLAGS);
    - } while (this_cpu_cmpxchg(irq_work_list, next, entry) != next);
    + llist_add(&work->llnode, &irq_work_list->llist);

    /* The list was empty, raise self-interrupt to start processing. */
    - if (!irq_work_next(entry))
    + if (!test_and_set_bit(LIST_NONEMPTY_BIT, &irq_work_list->flags))
    arch_irq_work_raise();

    - preempt_enable();
    + put_cpu_var(irq_work_list);
    }

    /*
    @@ -100,16 +81,16 @@ static void __irq_work_queue(struct irq_
    *
    * Can be re-enqueued while the callback is still in progress.
    */
    -bool irq_work_queue(struct irq_work *entry)
    +bool irq_work_queue(struct irq_work *work)
    {
    - if (!irq_work_claim(entry)) {
    + if (!irq_work_claim(work)) {
    /*
    * Already enqueued, can't do!
    */
    return false;
    }

    - __irq_work_queue(entry);
    + __irq_work_queue(work);
    return true;
    }
    EXPORT_SYMBOL_GPL(irq_work_queue);
    @@ -120,34 +101,35 @@ EXPORT_SYMBOL_GPL(irq_work_queue);
    */
    void irq_work_run(void)
    {
    - struct irq_work *list;
    + struct irq_work *work;
    + struct irq_work_list *irq_work_list;
    + struct llist_node *llnode;

    - if (this_cpu_read(irq_work_list) == NULL)
    + irq_work_list = &__get_cpu_var(irq_work_lists);
    + if (llist_empty(&irq_work_list->llist))
    return;

    BUG_ON(!in_irq());
    BUG_ON(!irqs_disabled());

    - list = this_cpu_xchg(irq_work_list, NULL);
    -
    - while (list != NULL) {
    - struct irq_work *entry = list;
    + clear_bit(LIST_NONEMPTY_BIT, &irq_work_list->flags);
    + llnode = llist_del_all(&irq_work_list->llist);
    + while (llnode != NULL) {
    + work = llist_entry(llnode, struct irq_work, llnode);

    - list = irq_work_next(list);
    + llnode = llnode->next;

    /*
    - * Clear the PENDING bit, after this point the @entry
    + * Clear the PENDING bit, after this point the @work
    * can be re-used.
    */
    - entry->next = next_flags(NULL, IRQ_WORK_BUSY);
    - entry->func(entry);
    + work->flags = IRQ_WORK_BUSY;
    + work->func(work);
    /*
    * Clear the BUSY bit and return to the free state if
    * no-one else claimed it meanwhile.
    */
    - (void)cmpxchg(&entry->next,
    - next_flags(NULL, IRQ_WORK_BUSY),
    - NULL);
    + (void)cmpxchg(&work->flags, IRQ_WORK_BUSY, 0);
    }
    }
    EXPORT_SYMBOL_GPL(irq_work_run);
    @@ -156,11 +138,11 @@ EXPORT_SYMBOL_GPL(irq_work_run);
    * Synchronize against the irq_work @entry, ensures the entry is not
    * currently in use.
    */
    -void irq_work_sync(struct irq_work *entry)
    +void irq_work_sync(struct irq_work *work)
    {
    WARN_ON_ONCE(irqs_disabled());

    - while (irq_work_is_set(entry, IRQ_WORK_BUSY))
    + while (work->flags & IRQ_WORK_BUSY)
    cpu_relax();
    }
    EXPORT_SYMBOL_GPL(irq_work_sync);

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