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

[David Vrabel <david.vrabel@xxxxxxxxxx>]

From: Malcolm Crossley <malcolm.crossley@xxxxxxxxxx>

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 <malcolm.crossley@xxxxxxxxxx>
Signed-off-by: David Vrabel <david.vrabel@xxxxxxxxxx>
---
 drivers/net/xen-netfront.c | 15 +++------------
 1 file changed, 3 insertions(+), 12 deletions(-)

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);
 }
-- 
2.1.4


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