[Xen-devel] [PATCHv1 net] xen-netback: notify immediately after pushing Tx response.

[David Vrabel <david.vrabel@xxxxxxxxxx>]

This fixes a performance regression introduced by
7fbb9d8415d4a51cf542e87cf3a717a9f7e6aedc (xen-netback: release pending
index before pushing Tx responses)

Moving the notify outside of the spin locks means it can be delayed a
long time (if the dealloc thread is descheduled or there is an
interrupt or softirq).

Signed-off-by: David Vrabel <david.vrabel@xxxxxxxxxx>
---
 drivers/net/xen-netback/netback.c |   23 ++++++++++++-----------
 1 file changed, 12 insertions(+), 11 deletions(-)

diff --git a/drivers/net/xen-netback/netback.c 
b/drivers/net/xen-netback/netback.c
index c4d68d7..7f8a466 100644
--- a/drivers/net/xen-netback/netback.c
+++ b/drivers/net/xen-netback/netback.c
@@ -96,6 +96,7 @@ static void xenvif_idx_release(struct xenvif_queue *queue, 
u16 pending_idx,
 static void make_tx_response(struct xenvif_queue *queue,
                             struct xen_netif_tx_request *txp,
                             s8       st);
+static void push_tx_responses(struct xenvif_queue *queue);
 
 static inline int tx_work_todo(struct xenvif_queue *queue);
 
@@ -655,15 +656,10 @@ static void xenvif_tx_err(struct xenvif_queue *queue,
        unsigned long flags;
 
        do {
-               int notify;
-
                spin_lock_irqsave(&queue->response_lock, flags);
                make_tx_response(queue, txp, XEN_NETIF_RSP_ERROR);
-               RING_PUSH_RESPONSES_AND_CHECK_NOTIFY(&queue->tx, notify);
+               push_tx_responses(queue);
                spin_unlock_irqrestore(&queue->response_lock, flags);
-               if (notify)
-                       notify_remote_via_irq(queue->tx_irq);
-
                if (cons == end)
                        break;
                txp = RING_GET_REQUEST(&queue->tx, cons++);
@@ -1655,7 +1651,6 @@ static void xenvif_idx_release(struct xenvif_queue 
*queue, u16 pending_idx,
 {
        struct pending_tx_info *pending_tx_info;
        pending_ring_idx_t index;
-       int notify;
        unsigned long flags;
 
        pending_tx_info = &queue->pending_tx_info[pending_idx];
@@ -1671,12 +1666,9 @@ static void xenvif_idx_release(struct xenvif_queue 
*queue, u16 pending_idx,
        index = pending_index(queue->pending_prod++);
        queue->pending_ring[index] = pending_idx;
 
-       RING_PUSH_RESPONSES_AND_CHECK_NOTIFY(&queue->tx, notify);
+       push_tx_responses(queue);
 
        spin_unlock_irqrestore(&queue->response_lock, flags);
-
-       if (notify)
-               notify_remote_via_irq(queue->tx_irq);
 }
 
 
@@ -1697,6 +1689,15 @@ static void make_tx_response(struct xenvif_queue *queue,
        queue->tx.rsp_prod_pvt = ++i;
 }
 
+static void push_tx_responses(struct xenvif_queue *queue)
+{
+       int notify;
+
+       RING_PUSH_RESPONSES_AND_CHECK_NOTIFY(&queue->tx, notify);
+       if (notify)
+               notify_remote_via_irq(queue->tx_irq);
+}
+
 static struct xen_netif_rx_response *make_rx_response(struct xenvif_queue 
*queue,
                                             u16      id,
                                             s8       st,
-- 
1.7.10.4


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