@@ -1105,6 +1105,11 @@ static inline void iocb_destroy(struct aio_kiocb *iocb)
kmem_cache_free(kiocb_cachep, iocb);
}
+struct aio_waiter {
+ struct wait_queue_entry w;
+ size_t min_nr;
+};
+
/* aio_complete
* Called when the io request on the given iocb is complete.
*/
@@ -1113,7 +1118,7 @@ static void aio_complete(struct aio_kiocb *iocb)
struct kioctx *ctx = iocb->ki_ctx;
struct aio_ring *ring;
struct io_event *ev_page, *event;
- unsigned tail, pos, head;
+ unsigned tail, pos, head, avail;
unsigned long flags;
/*
@@ -1157,6 +1162,10 @@ static void aio_complete(struct aio_kiocb *iocb)
ctx->completed_events++;
if (ctx->completed_events > 1)
refill_reqs_available(ctx, head, tail);
+
+ avail = tail > head
+ ? tail - head
+ : tail + ctx->nr_events - head;
spin_unlock_irqrestore(&ctx->completion_lock, flags);
pr_debug("added to ring %p at [%u]\n", iocb, tail);
@@ -1177,8 +1186,18 @@ static void aio_complete(struct aio_kiocb *iocb)
*/
smp_mb();
- if (waitqueue_active(&ctx->wait))
- wake_up(&ctx->wait);
+ if (waitqueue_active(&ctx->wait)) {
+ struct aio_waiter *curr, *next;
+ unsigned long flags;
+
+ spin_lock_irqsave(&ctx->wait.lock, flags);
+ list_for_each_entry_safe(curr, next, &ctx->wait.head, w.entry)
+ if (avail >= curr->min_nr) {
+ list_del_init_careful(&curr->w.entry);
+ wake_up_process(curr->w.private);
+ }
+ spin_unlock_irqrestore(&ctx->wait.lock, flags);
+ }
}
static inline void iocb_put(struct aio_kiocb *iocb)
@@ -1294,7 +1313,9 @@ static long read_events(struct kioctx *ctx, long min_nr, long nr,
struct io_event __user *event,
ktime_t until)
{
- long ret = 0;
+ struct hrtimer_sleeper t;
+ struct aio_waiter w;
+ long ret = 0, ret2 = 0;
/*
* Note that aio_read_events() is being called as the conditional - i.e.
@@ -1310,12 +1331,34 @@ static long read_events(struct kioctx *ctx, long min_nr, long nr,
* the ringbuffer empty. So in practice we should be ok, but it's
* something to be aware of when touching this code.
*/
- if (until == 0)
- aio_read_events(ctx, min_nr, nr, event, &ret);
- else
- wait_event_interruptible_hrtimeout(ctx->wait,
- aio_read_events(ctx, min_nr, nr, event, &ret),
- until);
+ aio_read_events(ctx, min_nr, nr, event, &ret);
+ if (until == 0 || ret < 0 || ret >= min_nr)
+ return ret;
+
+ hrtimer_init_sleeper_on_stack(&t, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
+ if (until != KTIME_MAX) {
+ hrtimer_set_expires_range_ns(&t.timer, until, current->timer_slack_ns);
+ hrtimer_sleeper_start_expires(&t, HRTIMER_MODE_REL);
+ }
+
+ init_wait(&w.w);
+
+ while (1) {
+ w.min_nr = min_nr - ret;
+
+ ret2 = prepare_to_wait_event(&ctx->wait, &w.w, TASK_INTERRUPTIBLE) ?:
+ !t.task ? -ETIME : 0;
+
+ if (aio_read_events(ctx, min_nr, nr, event, &ret) || ret2)
+ break;
+
+ schedule();
+ }
+
+ finish_wait(&ctx->wait, &w.w);
+ hrtimer_cancel(&t.timer);
+ destroy_hrtimer_on_stack(&t.timer);
+
return ret;
}
I've been observing workloads where IPIs due to wakeups in aio_complete() are ~15% of total CPU time in the profile. Most of those wakeups are unnecessary when completion batching is in use in io_getevents(). This plumbs min_nr through via the wait eventry, so that aio_complete() can avoid doing unnecessary wakeups. Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev> Cc: Benjamin LaHaise <bcrl@kvack.org Cc: linux-aio@kvack.org Cc: linux-fsdevel@vger.kernel.org --- fs/aio.c | 63 +++++++++++++++++++++++++++++++++++++++++++++++--------- 1 file changed, 53 insertions(+), 10 deletions(-)