[PATCHv1,net] xen-netfront: request Tx response events more often

Commit Message

David Vrabel Jan. 15, 2016, 11:56 a.m. UTC

From: Malcolm Crossley <[e-mail]>

Trying to batch Tx response events results in poor performance because
this delays freeing the transmitted skbs.

Instead use the standard RING_FINAL_CHECK_FOR_RESPONSES() macro to be
notified once the next Tx response is placed on the ring.

Signed-off-by: Malcolm Crossley <[e-mail]>
Signed-off-by: David Vrabel <[e-mail]>
---
 drivers/net/xen-netfront.c | 15 +++------------
 1 file changed, 3 insertions(+), 12 deletions(-)

Comments

David Miller Jan. 15, 2016, 7:58 p.m. UTC | #1

From: David Vrabel <[e-mail]>
Date: Fri, 15 Jan 2016 11:56:42 +0000

> @@ -364,6 +364,7 @@ static void xennet_tx_buf_gc(struct netfront_queue *queue)
>  	RING_IDX cons, prod;
>  	unsigned short id;
>  	struct sk_buff *skb;
> +	int more_to_do;

I hate to be difficult, but could you please use 'bool' for this variable?

Thanks!

Patch

diff --git a/drivers/net/xen-netfront.c b/drivers/net/xen-netfront.c
index d6abf19..9cb45be 100644
--- a/drivers/net/xen-netfront.c
+++ b/drivers/net/xen-netfront.c
@@ -364,6 +364,7 @@  static void xennet_tx_buf_gc(struct netfront_queue *queue)
 	RING_IDX cons, prod;
 	unsigned short id;
 	struct sk_buff *skb;
+	int more_to_do;
 
 	BUG_ON(!netif_carrier_ok(queue->info->netdev));
 
@@ -398,18 +399,8 @@  static void xennet_tx_buf_gc(struct netfront_queue *queue)
 
 		queue->tx.rsp_cons = prod;
 
-		/*
-		 * Set a new event, then check for race with update of tx_cons.
-		 * Note that it is essential to schedule a callback, no matter
-		 * how few buffers are pending. Even if there is space in the
-		 * transmit ring, higher layers may be blocked because too much
-		 * data is outstanding: in such cases notification from Xen is
-		 * likely to be the only kick that we'll get.
-		 */
-		queue->tx.sring->rsp_event =
-			prod + ((queue->tx.sring->req_prod - prod) >> 1) + 1;
-		mb();		/* update shared area */
-	} while ((cons == prod) && (prod != queue->tx.sring->rsp_prod));
+		RING_FINAL_CHECK_FOR_RESPONSES(&queue->tx, more_to_do);
+	} while (more_to_do);
 
 	xennet_maybe_wake_tx(queue);
 }