[patch v2 8/8]block: fiops sync preempts async

[Shaohua Li]

Debug patch only.

This implements CFQ like sync preempts async. But like CFQ, this
will starve async.

---
 block/fiops-iosched.c |   15 +++++++++++++++
 1 file changed, 15 insertions(+)

Index: linux/block/fiops-iosched.c
===================================================================
--- linux.orig/block/fiops-iosched.c	2012-01-21 10:35:04.000000000 +0800
+++ linux/block/fiops-iosched.c	2012-01-21 10:48:52.000000000 +0800
@@ -408,6 +408,21 @@ static struct fiops_ioc *fiops_select_io
 		return NULL;
 	}
 
+	/* Let sync request preempt async queue */
+	if (!rq_is_sync(rq) && service_tree->count > 1) {
+		struct rb_node *tmp = rb_next(&ioc->rb_node);
+		struct fiops_ioc *sync_ioc = NULL;
+		while (tmp) {
+			sync_ioc = rb_entry(tmp, struct fiops_ioc, rb_node);
+			rq = rq_entry_fifo(sync_ioc->fifo.next);
+			if (rq_is_sync(rq))
+				break;
+			tmp = rb_next(&sync_ioc->rb_node);
+		}
+		if (sync_ioc)
+			ioc = sync_ioc;
+	}
+
 	return ioc;
 }
 

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