irq_work: Add generic hardirq context callbacks

Provide a mechanism that allows running code in IRQ context. It is
most useful for NMI code that needs to interact with the rest of the
system -- like wakeup a task to drain buffers.

Perf currently has such a mechanism, so extract that and provide it as
a generic feature, independent of perf so that others may also
benefit.

The IRQ context callback is generated through self-IPIs where
possible, or on architectures like powerpc the decrementer (the
built-in timer facility) is set to generate an interrupt immediately.

Architectures that don't have anything like this get to do with a
callback from the timer tick. These architectures can call
irq_work_run() at the tail of any IRQ handlers that might enqueue such
work (like the perf IRQ handler) to avoid undue latencies in
processing the work.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Acked-by: Kyle McMartin <kyle@mcmartin.ca>
Acked-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
[ various fixes ]
Signed-off-by: Huang Ying <ying.huang@intel.com>
LKML-Reference: <1287036094.7768.291.camel@yhuang-dev>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 5 insertions, 99 deletions

diff --git a/kernel/perf_event.c b/kernel/perf_event.c
index 634f86a4b2f9..99b9700e74d0 100644
--- a/kernel/perf_event.c
+++ b/kernel/perf_event.c
@@ -2206,12 +2206,11 @@ static void free_event_rcu(struct rcu_head *head)
         kfree(event);
 }
 
-static void perf_pending_sync(struct perf_event *event);
 static void perf_buffer_put(struct perf_buffer *buffer);
 
 static void free_event(struct perf_event *event)
 {
-        perf_pending_sync(event);
+        irq_work_sync(&event->pending);
 
         if (!event->parent) {
                 atomic_dec(&nr_events);
@@ -3162,16 +3161,7 @@ void perf_event_wakeup(struct perf_event *event)
         }
 }
 
-/*
- * Pending wakeups
- *
- * Handle the case where we need to wakeup up from NMI (or rq->lock) context.
- *
- * The NMI bit means we cannot possibly take locks. Therefore, maintain a
- * single linked list and use cmpxchg() to add entries lockless.
- */
-
-static void perf_pending_event(struct perf_pending_entry *entry)
+static void perf_pending_event(struct irq_work *entry)
 {
         struct perf_event *event = container_of(entry,
                         struct perf_event, pending);
@@ -3187,89 +3177,6 @@ static void perf_pending_event(struct perf_pending_entry *entry)
         }
 }
 
-#define PENDING_TAIL ((struct perf_pending_entry *)-1UL)
-
-static DEFINE_PER_CPU(struct perf_pending_entry *, perf_pending_head) = {
-        PENDING_TAIL,
-};
-
-static void perf_pending_queue(struct perf_pending_entry *entry,
-                               void (*func)(struct perf_pending_entry *))
-{
-        struct perf_pending_entry **head;
-
-        if (cmpxchg(&entry->next, NULL, PENDING_TAIL) != NULL)
-                return;
-
-        entry->func = func;
-
-        head = &get_cpu_var(perf_pending_head);
-
-        do {
-                entry->next = *head;
-        } while (cmpxchg(head, entry->next, entry) != entry->next);
-
-        set_perf_event_pending();
-
-        put_cpu_var(perf_pending_head);
-}
-
-static int __perf_pending_run(void)
-{
-        struct perf_pending_entry *list;
-        int nr = 0;
-
-        list = xchg(&__get_cpu_var(perf_pending_head), PENDING_TAIL);
-        while (list != PENDING_TAIL) {
-                void (*func)(struct perf_pending_entry *);
-                struct perf_pending_entry *entry = list;
-
-                list = list->next;
-
-                func = entry->func;
-                entry->next = NULL;
-                /*
-                 * Ensure we observe the unqueue before we issue the wakeup,
-                 * so that we won't be waiting forever.
-                 * -- see perf_not_pending().
-                 */
-                smp_wmb();
-
-                func(entry);
-                nr++;
-        }
-
-        return nr;
-}
-
-static inline int perf_not_pending(struct perf_event *event)
-{
-        /*
-         * If we flush on whatever cpu we run, there is a chance we don't
-         * need to wait.
-         */
-        get_cpu();
-        __perf_pending_run();
-        put_cpu();
-
-        /*
-         * Ensure we see the proper queue state before going to sleep
-         * so that we do not miss the wakeup. -- see perf_pending_handle()
-         */
-        smp_rmb();
-        return event->pending.next == NULL;
-}
-
-static void perf_pending_sync(struct perf_event *event)
-{
-        wait_event(event->waitq, perf_not_pending(event));
-}
-
-void perf_event_do_pending(void)
-{
-        __perf_pending_run();
-}
-
 /*
  * We assume there is only KVM supporting the callbacks.
  * Later on, we might change it to a list if there is
@@ -3319,8 +3226,7 @@ static void perf_output_wakeup(struct perf_output_handle *handle)
 
         if (handle->nmi) {
                 handle->event->pending_wakeup = 1;
-                perf_pending_queue(&handle->event->pending,
-                                   perf_pending_event);
+                irq_work_queue(&handle->event->pending);
         } else
                 perf_event_wakeup(handle->event);
 }
@@ -4356,8 +4262,7 @@ static int __perf_event_overflow(struct perf_event *event, int nmi,
                 event->pending_kill = POLL_HUP;
                 if (nmi) {
                         event->pending_disable = 1;
-                        perf_pending_queue(&event->pending,
-                                           perf_pending_event);
+                        irq_work_queue(&event->pending);
                 } else
                         perf_event_disable(event);
         }
@@ -5374,6 +5279,7 @@ perf_event_alloc(struct perf_event_attr *attr, int cpu,
         INIT_LIST_HEAD(&event->event_entry);
         INIT_LIST_HEAD(&event->sibling_list);
         init_waitqueue_head(&event->waitq);
+        init_irq_work(&event->pending, perf_pending_event);
 
         mutex_init(&event->mmap_mutex);