[PATCH] xen-netfront: Rework the fix for Rx stall during OOM and network stress

[PATCH] xen-netfront: Rework the fix for Rx stall during OOM and network stress

[Vineeth Remanan Pillai]

The commit 90c311b0eeea ("xen-netfront: Fix Rx stall during network
stress and OOM") caused the refill timer to be triggerred almost on
all invocations of xennet_alloc_rx_buffers for certain workloads.
This reworks the fix by reverting to the old behaviour and taking into
consideration the skb allocation failure. Refill timer is now triggered
on insufficient requests or skb allocation failure.

Signed-off-by: Vineeth Remanan Pillai <vineethp@amazon.com>
Fixes: 90c311b0eeea (xen-netfront: Fix Rx stall during network stress and OOM)
Reported-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
---
 drivers/net/xen-netfront.c | 14 +++++++++++---
 1 file changed, 11 insertions(+), 3 deletions(-)

diff --git a/drivers/net/xen-netfront.c b/drivers/net/xen-netfront.c
index 8315fe7..9dba697 100644
--- a/drivers/net/xen-netfront.c
+++ b/drivers/net/xen-netfront.c
@@ -281,6 +281,7 @@ static void xennet_alloc_rx_buffers(struct netfront_queue *queue)
 {
 	RING_IDX req_prod = queue->rx.req_prod_pvt;
 	int notify;
+	int err = 0;
 
 	if (unlikely(!netif_carrier_ok(queue->info->netdev)))
 		return;
@@ -295,8 +296,10 @@ static void xennet_alloc_rx_buffers(struct netfront_queue *queue)
 		struct xen_netif_rx_request *req;
 
 		skb = xennet_alloc_one_rx_buffer(queue);
-		if (!skb)
+		if (!skb) {
+			err = -ENOMEM;
 			break;
+		}
 
 		id = xennet_rxidx(req_prod);
 
@@ -320,8 +323,13 @@ static void xennet_alloc_rx_buffers(struct netfront_queue *queue)
 
 	queue->rx.req_prod_pvt = req_prod;
 
-	/* Not enough requests? Try again later. */
-	if (req_prod - queue->rx.sring->req_prod < NET_RX_SLOTS_MIN) {
+	/* Try again later if there are not enough requests or skb allocation
+	 * failed.
+	 * Enough requests is quantified as the sum of newly created slots and
+	 * the unconsumed slots at the backend.
+	 */
+	if (req_prod - queue->rx.rsp_cons < NET_RX_SLOTS_MIN ||
+	    unlikely(err)) {
 		mod_timer(&queue->rx_refill_timer, jiffies + (HZ/10));
 		return;
 	}
-- 
2.1.2.AMZN

Re: [PATCH] xen-netfront: Rework the fix for Rx stall during OOM and network stress

[Boris Ostrovsky]

On 02/07/2017 01:59 PM, Vineeth Remanan Pillai wrote:
> The commit 90c311b0eeea ("xen-netfront: Fix Rx stall during network
> stress and OOM") caused the refill timer to be triggerred almost on
> all invocations of xennet_alloc_rx_buffers for certain workloads.
> This reworks the fix by reverting to the old behaviour and taking into
> consideration the skb allocation failure. Refill timer is now triggered
> on insufficient requests or skb allocation failure.
>
> Signed-off-by: Vineeth Remanan Pillai <vineethp@amazon.com>
> Fixes: 90c311b0eeea (xen-netfront: Fix Rx stall during network stress and OOM)
> Reported-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>

Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>

Re: [PATCH] xen-netfront: Rework the fix for Rx stall during OOM and network stress

[David Miller]

From: Vineeth Remanan Pillai <vineethp@amazon.com>
Date: Tue, 7 Feb 2017 18:59:01 +0000

> The commit 90c311b0eeea ("xen-netfront: Fix Rx stall during network
> stress and OOM") caused the refill timer to be triggerred almost on
> all invocations of xennet_alloc_rx_buffers for certain workloads.
> This reworks the fix by reverting to the old behaviour and taking into
> consideration the skb allocation failure. Refill timer is now triggered
> on insufficient requests or skb allocation failure.
> 
> Signed-off-by: Vineeth Remanan Pillai <vineethp@amazon.com>
> Fixes: 90c311b0eeea (xen-netfront: Fix Rx stall during network stress and OOM)
> Reported-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>

Applied.