linux-kernel - [patch] aio: streamline read events after woken up

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Date:	Fri, 29 Dec 2006 18:49:39 -0800
From:	"Chen, Kenneth W" <kenneth.w.chen@...el.com>
To:	"'Andrew Morton'" <akpm@...l.org>, <zach.brown@...cle.com>
Cc:	<linux-aio@...ck.org>, <linux-kernel@...r.kernel.org>,
	"'Benjamin LaHaise'" <bcrl@...ck.org>, <suparna@...ibm.com>
Subject: [patch] aio: streamline read events after woken up

The read event loop in the blocking path is also inefficient. For every
event it reap (if not blocking), it does the following in a loop:

      while (i < nr) {
            prepare_to_wait_exclusive
            aio_read_evt
            finish_wait
            ...
      }

Given the previous patch "aio: add per task aio wait event condition"
that we properly wake up event waiting process knowing that we have
enough events to reap, it's just plain waste of time to insert itself
into a wait queue, and then immediately remove itself from the wait
queue for *every* event reap iteration.

This patch factors out the wait queue insertion/deletion out of the event
reap loop, streamlines the event reaping after the process wakes up.


Signed-off-by: Ken Chen <kenneth.w.chen@...el.com>

--- ./fs/aio.c.orig	2006-12-24 17:04:52.000000000 -0800
+++ ./fs/aio.c	2006-12-24 17:05:10.000000000 -0800
@@ -1174,42 +1174,40 @@ retry:
 	}
 
 	aio_init_wait(&wait);
+wait:
+	prepare_to_wait_exclusive(&ctx->wait, &wait.wait, TASK_INTERRUPTIBLE);
+	ret = aio_read_evt(ctx, &ent);
+	if (!ret) {
+		wait.nr_wait = min_nr - i;
+		schedule();
+		if (signal_pending(tsk))
+			ret = -EINTR;
+	}
+	finish_wait(&ctx->wait, &wait.wait);
+
+	if (ret < 0)
+		goto out_cleanup;
+
 	while (likely(i < nr)) {
-		do {
-			prepare_to_wait_exclusive(&ctx->wait, &wait.wait,
-						  TASK_INTERRUPTIBLE);
-			ret = aio_read_evt(ctx, &ent);
-			if (ret)
-				break;
-			if (min_nr <= i)
-				break;
-			ret = 0;
-			if (to.timed_out)	/* Only check after read evt */
-				break;
-			wait.nr_wait = min_nr - i;
-			schedule();
-			if (signal_pending(tsk)) {
-				ret = -EINTR;
+		if (ret) {
+			if (unlikely(copy_to_user(event, &ent, sizeof(ent)))) {
+				dprintk("aio: lost an event due to EFAULT.\n");
+				ret = -EFAULT;
 				break;
 			}
-			/*ret = aio_read_evt(ctx, &ent);*/
-		} while (1) ;
-		finish_wait(&ctx->wait, &wait.wait);
-
-		if (unlikely(ret <= 0))
-			break;
+			event++;
+			i++;
+		}
 
-		ret = -EFAULT;
-		if (unlikely(copy_to_user(event, &ent, sizeof(ent)))) {
-			dprintk("aio: lost an event due to EFAULT.\n");
+		ret = aio_read_evt(ctx, &ent);
+		if (unlikely(!ret)) {
+			if (i < min_nr && !to.timed_out)
+				goto wait;
 			break;
 		}
-
-		/* Good, event copied to userland, update counts. */
-		event ++;
-		i ++;
 	}
 
+out_cleanup:
 	if (timeout)
 		clear_timeout(&to);
 out:
-
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