Revert "xen-netback: Aggregate TX unmap operations"

This reverts commit e9275f5e. This commit is the
last in the netback grant mapping series, and it tries to do more aggressive
aggreagtion of unmap operations. However practical use showed almost no
positive effect, whilst with certain frontends it causes significant performance
regression.
Signed-off-by: NZoltan Kiss <zoltan.kiss@citrix.com>
Acked-by: NIan Campbell <ian.campbell@citrix.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/xen-netback/common.h

@@ -137,8 +137,6 @@ struct xenvif {
 	u16 dealloc_ring[MAX_PENDING_REQS];
 	struct task_struct *dealloc_task;
 	wait_queue_head_t dealloc_wq;
-	struct timer_list dealloc_delay;
-	bool dealloc_delay_timed_out;
 
 	/* Use kthread for guest RX */
 	struct task_struct *task;

drivers/net/xen-netback/interface.c

@@ -407,7 +407,6 @@ struct xenvif *xenvif_alloc(struct device *parent, domid_t domid,
 			  .desc = i };
 		vif->grant_tx_handle[i] = NETBACK_INVALID_HANDLE;
 	}
-	init_timer(&vif->dealloc_delay);
 
 	/*
 	 * Initialise a dummy MAC address. We choose the numerically
@@ -556,7 +555,6 @@ void xenvif_disconnect(struct xenvif *vif)
 	}
 
 	if (vif->dealloc_task) {
-		del_timer_sync(&vif->dealloc_delay);
 		kthread_stop(vif->dealloc_task);
 		vif->dealloc_task = NULL;
 	}

drivers/net/xen-netback/netback.c

@@ -133,11 +133,6 @@ static inline pending_ring_idx_t pending_index(unsigned i)
 	return i & (MAX_PENDING_REQS-1);
 }
 
-static inline pending_ring_idx_t nr_free_slots(struct xen_netif_tx_back_ring *ring)
-{
-	return ring->nr_ents -	(ring->sring->req_prod - ring->rsp_prod_pvt);
-}
-
 bool xenvif_rx_ring_slots_available(struct xenvif *vif, int needed)
 {
 	RING_IDX prod, cons;
@@ -1718,36 +1713,9 @@ static inline int tx_work_todo(struct xenvif *vif)
 	return 0;
 }
 
-static void xenvif_dealloc_delay(unsigned long data)
-{
-	struct xenvif *vif = (struct xenvif *)data;
-
-	vif->dealloc_delay_timed_out = true;
-	wake_up(&vif->dealloc_wq);
-}
-
 static inline bool tx_dealloc_work_todo(struct xenvif *vif)
 {
-	if (vif->dealloc_cons != vif->dealloc_prod) {
-		if ((nr_free_slots(&vif->tx) > 2 * XEN_NETBK_LEGACY_SLOTS_MAX) &&
-		    (vif->dealloc_prod - vif->dealloc_cons < MAX_PENDING_REQS / 4) &&
-		    !vif->dealloc_delay_timed_out) {
-			if (!timer_pending(&vif->dealloc_delay)) {
-				vif->dealloc_delay.function =
-					xenvif_dealloc_delay;
-				vif->dealloc_delay.data = (unsigned long)vif;
-				mod_timer(&vif->dealloc_delay,
-					  jiffies + msecs_to_jiffies(1));
-
-			}
-			return false;
-		}
-		del_timer_sync(&vif->dealloc_delay);
-		vif->dealloc_delay_timed_out = false;
-		return true;
-	}
-
-	return false;
+	return vif->dealloc_cons != vif->dealloc_prod;
 }
 
 void xenvif_unmap_frontend_rings(struct xenvif *vif)