[PATCH -mm -v2 5/5] irq_work, Use llist in irq_work

Huang Ying
2011-09-08T06:01:35Z

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 ++++---
kernel/irq_work.c | 92 ++++++++++++++++-------------------------------
2 files changed, 42 insertions(+), 65 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/kernel/irq_work.c
+++ b/kernel/irq_work.c
@@ -10,7 +10,6 @@
#include <linux/irq_work.h>
#include <linux/percpu.h>
#include <linux/hardirq.h>
-#include <asm/processor.h>

/*
* An entry can be in one of four states:
@@ -19,54 +18,34 @@
* 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;
-}
-
-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;
-}
-
-static DEFINE_PER_CPU(struct irq_work *, irq_work_list);
+static DEFINE_PER_CPU(struct llist_head, irq_work_list);

/*
* 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)
+ for (;;) {
+ 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;
+ if (cmpxchg(&work->flags, flags, nflags) == flags)
+ break;
+ cpu_relax();
+ }

return true;
}

-
void __weak arch_irq_work_raise(void)
{
/*
@@ -77,20 +56,15 @@ 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;
+ bool empty;

preempt_disable();

- 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);
-
+ empty = llist_add(&work->llnode, &__get_cpu_var(irq_work_list));
/* The list was empty, raise self-interrupt to start processing. */
- if (!irq_work_next(entry))
+ if (empty)
arch_irq_work_raise();

preempt_enable();
@@ -102,16 +76,16 @@ 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);
@@ -122,34 +96,34 @@ EXPORT_SYMBOL_GPL(irq_work_queue);
*/
void irq_work_run(void)
{
- struct irq_work *list;
+ struct irq_work *work;
+ struct llist_head *this_list;
+ struct llist_node *llnode;

- if (this_cpu_read(irq_work_list) == NULL)
+ this_list = &__get_cpu_var(irq_work_list);
+ if (llist_empty(this_list))
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;
+ llnode = llist_del_all(this_list);
+ 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);
@@ -158,11 +132,11 @@ 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);