[PATCHv1 net] xen-netback: support frontends without feature-rx-notify again

[PATCHv1 net] xen-netback: support frontends without feature-rx-notify again

[David Vrabel]

Commit bc96f648df1bbc2729abbb84513cf4f64273a1f1 (xen-netback: make
feature-rx-notify mandatory) incorrectly assumed that there were no
frontends in use that did not support this feature.  But the frontend
driver in MiniOS does not and since this is used by (qemu) stubdoms,
these stopped working.

Netback sort of works as-is in this mode except:

- If there are no Rx requests and the internal Rx queue fills, only
  the drain timeout will wake the thread.  The default drain timeout
  of 10 s would give unacceptable pauses.

- If an Rx stall was detected and the internal Rx queue is drained,
  then the Rx thread would never wake.

Handle these two cases (when feature-rx-notify is disabled) by:

- Reducing the drain timeout to 30 ms.

- Disabling Rx stall detection.

Reported-by: John <jw@nuclearfallout.net>
Tested-by: John <jw@nuclearfallout.net>
Signed-off-by: David Vrabel <david.vrabel@citrix.com>
---
 drivers/net/xen-netback/common.h    |    4 +++-
 drivers/net/xen-netback/interface.c |    4 +++-
 drivers/net/xen-netback/netback.c   |   27 ++++++++++++++-------------
 drivers/net/xen-netback/xenbus.c    |   12 +++++++++---
 4 files changed, 29 insertions(+), 18 deletions(-)

diff --git a/drivers/net/xen-netback/common.h b/drivers/net/xen-netback/common.h
index 083ecc9..5f1fda4 100644
--- a/drivers/net/xen-netback/common.h
+++ b/drivers/net/xen-netback/common.h
@@ -230,6 +230,8 @@ struct xenvif {
 	 */
 	bool disabled;
 	unsigned long status;
+	unsigned long drain_timeout;
+	unsigned long stall_timeout;
 
 	/* Queues */
 	struct xenvif_queue *queues;
@@ -328,7 +330,7 @@ irqreturn_t xenvif_interrupt(int irq, void *dev_id);
 extern bool separate_tx_rx_irq;
 
 extern unsigned int rx_drain_timeout_msecs;
-extern unsigned int rx_drain_timeout_jiffies;
+extern unsigned int rx_stall_timeout_msecs;
 extern unsigned int xenvif_max_queues;
 
 #ifdef CONFIG_DEBUG_FS
diff --git a/drivers/net/xen-netback/interface.c b/drivers/net/xen-netback/interface.c
index a6a32d3..9259a73 100644
--- a/drivers/net/xen-netback/interface.c
+++ b/drivers/net/xen-netback/interface.c
@@ -166,7 +166,7 @@ static int xenvif_start_xmit(struct sk_buff *skb, struct net_device *dev)
 		goto drop;
 
 	cb = XENVIF_RX_CB(skb);
-	cb->expires = jiffies + rx_drain_timeout_jiffies;
+	cb->expires = jiffies + vif->drain_timeout;
 
 	xenvif_rx_queue_tail(queue, skb);
 	xenvif_kick_thread(queue);
@@ -414,6 +414,8 @@ struct xenvif *xenvif_alloc(struct device *parent, domid_t domid,
 	vif->ip_csum = 1;
 	vif->dev = dev;
 	vif->disabled = false;
+	vif->drain_timeout = msecs_to_jiffies(rx_drain_timeout_msecs);
+	vif->stall_timeout = msecs_to_jiffies(rx_stall_timeout_msecs);
 
 	/* Start out with no queues. */
 	vif->queues = NULL;
diff --git a/drivers/net/xen-netback/netback.c b/drivers/net/xen-netback/netback.c
index 4a509f7..908e65e 100644
--- a/drivers/net/xen-netback/netback.c
+++ b/drivers/net/xen-netback/netback.c
@@ -60,14 +60,12 @@ module_param(separate_tx_rx_irq, bool, 0644);
  */
 unsigned int rx_drain_timeout_msecs = 10000;
 module_param(rx_drain_timeout_msecs, uint, 0444);
-unsigned int rx_drain_timeout_jiffies;
 
 /* The length of time before the frontend is considered unresponsive
  * because it isn't providing Rx slots.
  */
-static unsigned int rx_stall_timeout_msecs = 60000;
+unsigned int rx_stall_timeout_msecs = 60000;
 module_param(rx_stall_timeout_msecs, uint, 0444);
-static unsigned int rx_stall_timeout_jiffies;
 
 unsigned int xenvif_max_queues;
 module_param_named(max_queues, xenvif_max_queues, uint, 0644);
@@ -2020,7 +2018,7 @@ static bool xenvif_rx_queue_stalled(struct xenvif_queue *queue)
 	return !queue->stalled
 		&& prod - cons < XEN_NETBK_RX_SLOTS_MAX
 		&& time_after(jiffies,
-			      queue->last_rx_time + rx_stall_timeout_jiffies);
+			      queue->last_rx_time + queue->vif->stall_timeout);
 }
 
 static bool xenvif_rx_queue_ready(struct xenvif_queue *queue)
@@ -2038,8 +2036,9 @@ static bool xenvif_have_rx_work(struct xenvif_queue *queue)
 {
 	return (!skb_queue_empty(&queue->rx_queue)
 		&& xenvif_rx_ring_slots_available(queue, XEN_NETBK_RX_SLOTS_MAX))
-		|| xenvif_rx_queue_stalled(queue)
-		|| xenvif_rx_queue_ready(queue)
+		|| (queue->vif->stall_timeout &&
+		    (xenvif_rx_queue_stalled(queue)
+		     || xenvif_rx_queue_ready(queue)))
 		|| kthread_should_stop()
 		|| queue->vif->disabled;
 }
@@ -2092,6 +2091,9 @@ int xenvif_kthread_guest_rx(void *data)
 	struct xenvif_queue *queue = data;
 	struct xenvif *vif = queue->vif;
 
+	if (!vif->stall_timeout)
+		xenvif_queue_carrier_on(queue);
+
 	for (;;) {
 		xenvif_wait_for_rx_work(queue);
 
@@ -2118,10 +2120,12 @@ int xenvif_kthread_guest_rx(void *data)
 		 * while it's probably not responsive, drop the
 		 * carrier so packets are dropped earlier.
 		 */
-		if (xenvif_rx_queue_stalled(queue))
-			xenvif_queue_carrier_off(queue);
-		else if (xenvif_rx_queue_ready(queue))
-			xenvif_queue_carrier_on(queue);
+		if (vif->stall_timeout) {
+			if (xenvif_rx_queue_stalled(queue))
+				xenvif_queue_carrier_off(queue);
+			else if (xenvif_rx_queue_ready(queue))
+				xenvif_queue_carrier_on(queue);
+		}
 
 		/* Queued packets may have foreign pages from other
 		 * domains.  These cannot be queued indefinitely as
@@ -2192,9 +2196,6 @@ static int __init netback_init(void)
 	if (rc)
 		goto failed_init;
 
-	rx_drain_timeout_jiffies = msecs_to_jiffies(rx_drain_timeout_msecs);
-	rx_stall_timeout_jiffies = msecs_to_jiffies(rx_stall_timeout_msecs);
-
 #ifdef CONFIG_DEBUG_FS
 	xen_netback_dbg_root = debugfs_create_dir("xen-netback", NULL);
 	if (IS_ERR_OR_NULL(xen_netback_dbg_root))
diff --git a/drivers/net/xen-netback/xenbus.c b/drivers/net/xen-netback/xenbus.c
index d44cd19..efbaf2a 100644
--- a/drivers/net/xen-netback/xenbus.c
+++ b/drivers/net/xen-netback/xenbus.c
@@ -887,9 +887,15 @@ static int read_xenbus_vif_flags(struct backend_info *be)
 		return -EOPNOTSUPP;
 
 	if (xenbus_scanf(XBT_NIL, dev->otherend,
-			 "feature-rx-notify", "%d", &val) < 0 || val == 0) {
-		xenbus_dev_fatal(dev, -EINVAL, "feature-rx-notify is mandatory");
-		return -EINVAL;
+			 "feature-rx-notify", "%d", &val) < 0)
+		val = 0;
+	if (!val) {
+		/* - Reduce drain timeout to poll more frequently for
+		 *   Rx requests.
+		 * - Disable Rx stall detection.
+		 */
+		be->vif->drain_timeout = msecs_to_jiffies(30);
+		be->vif->stall_timeout = 0;
 	}
 
 	if (xenbus_scanf(XBT_NIL, dev->otherend, "feature-sg",
-- 
1.7.10.4

Re: [PATCHv1 net] xen-netback: support frontends without feature-rx-notify again

[Wei Liu]

On Thu, Dec 18, 2014 at 11:13:06AM +0000, David Vrabel wrote:
> Commit bc96f648df1bbc2729abbb84513cf4f64273a1f1 (xen-netback: make
> feature-rx-notify mandatory) incorrectly assumed that there were no
> frontends in use that did not support this feature.  But the frontend
> driver in MiniOS does not and since this is used by (qemu) stubdoms,
> these stopped working.
> 
> Netback sort of works as-is in this mode except:
> 
> - If there are no Rx requests and the internal Rx queue fills, only
>   the drain timeout will wake the thread.  The default drain timeout
>   of 10 s would give unacceptable pauses.
> 
> - If an Rx stall was detected and the internal Rx queue is drained,
>   then the Rx thread would never wake.
> 
> Handle these two cases (when feature-rx-notify is disabled) by:
> 
> - Reducing the drain timeout to 30 ms.
> 
> - Disabling Rx stall detection.
> 
> Reported-by: John <jw@nuclearfallout.net>
> Tested-by: John <jw@nuclearfallout.net>
> Signed-off-by: David Vrabel <david.vrabel@citrix.com>

Reviewed-by: Wei Liu <wei.liu2@citrix.com>

Re: [PATCHv1 net] xen-netback: support frontends without feature-rx-notify again

[Wei Liu]

On Thu, Dec 18, 2014 at 11:13:06AM +0000, David Vrabel wrote:
> Commit bc96f648df1bbc2729abbb84513cf4f64273a1f1 (xen-netback: make
> feature-rx-notify mandatory) incorrectly assumed that there were no
> frontends in use that did not support this feature.  But the frontend
> driver in MiniOS does not and since this is used by (qemu) stubdoms,
> these stopped working.
> 
> Netback sort of works as-is in this mode except:
> 
> - If there are no Rx requests and the internal Rx queue fills, only
>   the drain timeout will wake the thread.  The default drain timeout
>   of 10 s would give unacceptable pauses.
> 
> - If an Rx stall was detected and the internal Rx queue is drained,
>   then the Rx thread would never wake.
> 
> Handle these two cases (when feature-rx-notify is disabled) by:
> 
> - Reducing the drain timeout to 30 ms.
> 
> - Disabling Rx stall detection.
> 
> Reported-by: John <jw@nuclearfallout.net>
> Tested-by: John <jw@nuclearfallout.net>
> Signed-off-by: David Vrabel <david.vrabel@citrix.com>

Reviewed-by: Wei Liu <wei.liu2@citrix.com>

Re: [PATCHv1 net] xen-netback: support frontends without feature-rx-notify again

[David Miller]

From: David Vrabel <david.vrabel@citrix.com>
Date: Thu, 18 Dec 2014 11:13:06 +0000

> Commit bc96f648df1bbc2729abbb84513cf4f64273a1f1 (xen-netback: make
> feature-rx-notify mandatory) incorrectly assumed that there were no
> frontends in use that did not support this feature.  But the frontend
> driver in MiniOS does not and since this is used by (qemu) stubdoms,
> these stopped working.
> 
> Netback sort of works as-is in this mode except:
> 
> - If there are no Rx requests and the internal Rx queue fills, only
>   the drain timeout will wake the thread.  The default drain timeout
>   of 10 s would give unacceptable pauses.
> 
> - If an Rx stall was detected and the internal Rx queue is drained,
>   then the Rx thread would never wake.
> 
> Handle these two cases (when feature-rx-notify is disabled) by:
> 
> - Reducing the drain timeout to 30 ms.
> 
> - Disabling Rx stall detection.
> 
> Reported-by: John <jw@nuclearfallout.net>
> Tested-by: John <jw@nuclearfallout.net>
> Signed-off-by: David Vrabel <david.vrabel@citrix.com>

Applied, and I assume that 3.18 -stable needs this as well?

Thanks.

Re: [PATCHv1 net] xen-netback: support frontends without feature-rx-notify again

[David Miller]

From: David Vrabel <david.vrabel@citrix.com>
Date: Thu, 18 Dec 2014 11:13:06 +0000

> Commit bc96f648df1bbc2729abbb84513cf4f64273a1f1 (xen-netback: make
> feature-rx-notify mandatory) incorrectly assumed that there were no
> frontends in use that did not support this feature.  But the frontend
> driver in MiniOS does not and since this is used by (qemu) stubdoms,
> these stopped working.
> 
> Netback sort of works as-is in this mode except:
> 
> - If there are no Rx requests and the internal Rx queue fills, only
>   the drain timeout will wake the thread.  The default drain timeout
>   of 10 s would give unacceptable pauses.
> 
> - If an Rx stall was detected and the internal Rx queue is drained,
>   then the Rx thread would never wake.
> 
> Handle these two cases (when feature-rx-notify is disabled) by:
> 
> - Reducing the drain timeout to 30 ms.
> 
> - Disabling Rx stall detection.
> 
> Reported-by: John <jw@nuclearfallout.net>
> Tested-by: John <jw@nuclearfallout.net>
> Signed-off-by: David Vrabel <david.vrabel@citrix.com>

Applied, and I assume that 3.18 -stable needs this as well?

Thanks.

Re: [PATCHv1 net] xen-netback: support frontends without feature-rx-notify again

[David Vrabel]

On 18/12/14 17:50, David Miller wrote:
> From: David Vrabel <david.vrabel@citrix.com>
> Date: Thu, 18 Dec 2014 11:13:06 +0000
> 
>> Commit bc96f648df1bbc2729abbb84513cf4f64273a1f1 (xen-netback: make
>> feature-rx-notify mandatory) incorrectly assumed that there were no
>> frontends in use that did not support this feature.  But the frontend
>> driver in MiniOS does not and since this is used by (qemu) stubdoms,
>> these stopped working.
>>
>> Netback sort of works as-is in this mode except:
>>
>> - If there are no Rx requests and the internal Rx queue fills, only
>>   the drain timeout will wake the thread.  The default drain timeout
>>   of 10 s would give unacceptable pauses.
>>
>> - If an Rx stall was detected and the internal Rx queue is drained,
>>   then the Rx thread would never wake.
>>
>> Handle these two cases (when feature-rx-notify is disabled) by:
>>
>> - Reducing the drain timeout to 30 ms.
>>
>> - Disabling Rx stall detection.
>>
>> Reported-by: John <jw@nuclearfallout.net>
>> Tested-by: John <jw@nuclearfallout.net>
>> Signed-off-by: David Vrabel <david.vrabel@citrix.com>
> 
> Applied, and I assume that 3.18 -stable needs this as well?

Yes, please.  Without it, netback just doesn't work with an important
use case.

Thanks.

David

Re: [PATCHv1 net] xen-netback: support frontends without feature-rx-notify again

[David Vrabel]

On 18/12/14 17:50, David Miller wrote:
> From: David Vrabel <david.vrabel@citrix.com>
> Date: Thu, 18 Dec 2014 11:13:06 +0000
> 
>> Commit bc96f648df1bbc2729abbb84513cf4f64273a1f1 (xen-netback: make
>> feature-rx-notify mandatory) incorrectly assumed that there were no
>> frontends in use that did not support this feature.  But the frontend
>> driver in MiniOS does not and since this is used by (qemu) stubdoms,
>> these stopped working.
>>
>> Netback sort of works as-is in this mode except:
>>
>> - If there are no Rx requests and the internal Rx queue fills, only
>>   the drain timeout will wake the thread.  The default drain timeout
>>   of 10 s would give unacceptable pauses.
>>
>> - If an Rx stall was detected and the internal Rx queue is drained,
>>   then the Rx thread would never wake.
>>
>> Handle these two cases (when feature-rx-notify is disabled) by:
>>
>> - Reducing the drain timeout to 30 ms.
>>
>> - Disabling Rx stall detection.
>>
>> Reported-by: John <jw@nuclearfallout.net>
>> Tested-by: John <jw@nuclearfallout.net>
>> Signed-off-by: David Vrabel <david.vrabel@citrix.com>
> 
> Applied, and I assume that 3.18 -stable needs this as well?

Yes, please.  Without it, netback just doesn't work with an important
use case.

Thanks.

David

Re: [PATCHv1 net] xen-netback: support frontends without feature-rx-notify again

[Ian Campbell]

On Thu, 2014-12-18 at 11:13 +0000, David Vrabel wrote:
> Commit bc96f648df1bbc2729abbb84513cf4f64273a1f1 (xen-netback: make
> feature-rx-notify mandatory) incorrectly assumed that there were no
> frontends in use that did not support this feature.  But the frontend
> driver in MiniOS does not and since this is used by (qemu) stubdoms,
> these stopped working.
> 
> Netback sort of works as-is in this mode except:
> 
> - If there are no Rx requests and the internal Rx queue fills, only
>   the drain timeout will wake the thread.  The default drain timeout
>   of 10 s would give unacceptable pauses.
> 
> - If an Rx stall was detected and the internal Rx queue is drained,
>   then the Rx thread would never wake.
> 
> Handle these two cases (when feature-rx-notify is disabled) by:
> 
> - Reducing the drain timeout to 30 ms.
> 
> - Disabling Rx stall detection.
> 
> Reported-by: John <jw@nuclearfallout.net>
> Tested-by: John <jw@nuclearfallout.net>
> Signed-off-by: David Vrabel <david.vrabel@citrix.com>

FYI I've seen a report[0] that "Windows 2012 R2 domu with GPLPV drivers"
also suffered without feature-rx-notify support in the backend.

Ian.

[0] https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=767261#103

Re: [PATCHv1 net] xen-netback: support frontends without feature-rx-notify again

[Ian Campbell]

On Thu, 2014-12-18 at 11:13 +0000, David Vrabel wrote:
> Commit bc96f648df1bbc2729abbb84513cf4f64273a1f1 (xen-netback: make
> feature-rx-notify mandatory) incorrectly assumed that there were no
> frontends in use that did not support this feature.  But the frontend
> driver in MiniOS does not and since this is used by (qemu) stubdoms,
> these stopped working.
> 
> Netback sort of works as-is in this mode except:
> 
> - If there are no Rx requests and the internal Rx queue fills, only
>   the drain timeout will wake the thread.  The default drain timeout
>   of 10 s would give unacceptable pauses.
> 
> - If an Rx stall was detected and the internal Rx queue is drained,
>   then the Rx thread would never wake.
> 
> Handle these two cases (when feature-rx-notify is disabled) by:
> 
> - Reducing the drain timeout to 30 ms.
> 
> - Disabling Rx stall detection.
> 
> Reported-by: John <jw@nuclearfallout.net>
> Tested-by: John <jw@nuclearfallout.net>
> Signed-off-by: David Vrabel <david.vrabel@citrix.com>

FYI I've seen a report[0] that "Windows 2012 R2 domu with GPLPV drivers"
also suffered without feature-rx-notify support in the backend.

Ian.

[0] https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=767261#103

[PATCHv1 net] xen-netback: support frontends without feature-rx-notify again

[David Vrabel]

Commit bc96f648df1bbc2729abbb84513cf4f64273a1f1 (xen-netback: make
feature-rx-notify mandatory) incorrectly assumed that there were no
frontends in use that did not support this feature.  But the frontend
driver in MiniOS does not and since this is used by (qemu) stubdoms,
these stopped working.

Netback sort of works as-is in this mode except:

- If there are no Rx requests and the internal Rx queue fills, only
  the drain timeout will wake the thread.  The default drain timeout
  of 10 s would give unacceptable pauses.

- If an Rx stall was detected and the internal Rx queue is drained,
  then the Rx thread would never wake.

Handle these two cases (when feature-rx-notify is disabled) by:

- Reducing the drain timeout to 30 ms.

- Disabling Rx stall detection.

Reported-by: John <jw@nuclearfallout.net>
Tested-by: John <jw@nuclearfallout.net>
Signed-off-by: David Vrabel <david.vrabel@citrix.com>
---
 drivers/net/xen-netback/common.h    |    4 +++-
 drivers/net/xen-netback/interface.c |    4 +++-
 drivers/net/xen-netback/netback.c   |   27 ++++++++++++++-------------
 drivers/net/xen-netback/xenbus.c    |   12 +++++++++---
 4 files changed, 29 insertions(+), 18 deletions(-)

diff --git a/drivers/net/xen-netback/common.h b/drivers/net/xen-netback/common.h
index 083ecc9..5f1fda4 100644
--- a/drivers/net/xen-netback/common.h
+++ b/drivers/net/xen-netback/common.h
@@ -230,6 +230,8 @@ struct xenvif {
 	 */
 	bool disabled;
 	unsigned long status;
+	unsigned long drain_timeout;
+	unsigned long stall_timeout;
 
 	/* Queues */
 	struct xenvif_queue *queues;
@@ -328,7 +330,7 @@ irqreturn_t xenvif_interrupt(int irq, void *dev_id);
 extern bool separate_tx_rx_irq;
 
 extern unsigned int rx_drain_timeout_msecs;
-extern unsigned int rx_drain_timeout_jiffies;
+extern unsigned int rx_stall_timeout_msecs;
 extern unsigned int xenvif_max_queues;
 
 #ifdef CONFIG_DEBUG_FS
diff --git a/drivers/net/xen-netback/interface.c b/drivers/net/xen-netback/interface.c
index a6a32d3..9259a73 100644
--- a/drivers/net/xen-netback/interface.c
+++ b/drivers/net/xen-netback/interface.c
@@ -166,7 +166,7 @@ static int xenvif_start_xmit(struct sk_buff *skb, struct net_device *dev)
 		goto drop;
 
 	cb = XENVIF_RX_CB(skb);
-	cb->expires = jiffies + rx_drain_timeout_jiffies;
+	cb->expires = jiffies + vif->drain_timeout;
 
 	xenvif_rx_queue_tail(queue, skb);
 	xenvif_kick_thread(queue);
@@ -414,6 +414,8 @@ struct xenvif *xenvif_alloc(struct device *parent, domid_t domid,
 	vif->ip_csum = 1;
 	vif->dev = dev;
 	vif->disabled = false;
+	vif->drain_timeout = msecs_to_jiffies(rx_drain_timeout_msecs);
+	vif->stall_timeout = msecs_to_jiffies(rx_stall_timeout_msecs);
 
 	/* Start out with no queues. */
 	vif->queues = NULL;
diff --git a/drivers/net/xen-netback/netback.c b/drivers/net/xen-netback/netback.c
index 4a509f7..908e65e 100644
--- a/drivers/net/xen-netback/netback.c
+++ b/drivers/net/xen-netback/netback.c
@@ -60,14 +60,12 @@ module_param(separate_tx_rx_irq, bool, 0644);
  */
 unsigned int rx_drain_timeout_msecs = 10000;
 module_param(rx_drain_timeout_msecs, uint, 0444);
-unsigned int rx_drain_timeout_jiffies;
 
 /* The length of time before the frontend is considered unresponsive
  * because it isn't providing Rx slots.
  */
-static unsigned int rx_stall_timeout_msecs = 60000;
+unsigned int rx_stall_timeout_msecs = 60000;
 module_param(rx_stall_timeout_msecs, uint, 0444);
-static unsigned int rx_stall_timeout_jiffies;
 
 unsigned int xenvif_max_queues;
 module_param_named(max_queues, xenvif_max_queues, uint, 0644);
@@ -2020,7 +2018,7 @@ static bool xenvif_rx_queue_stalled(struct xenvif_queue *queue)
 	return !queue->stalled
 		&& prod - cons < XEN_NETBK_RX_SLOTS_MAX
 		&& time_after(jiffies,
-			      queue->last_rx_time + rx_stall_timeout_jiffies);
+			      queue->last_rx_time + queue->vif->stall_timeout);
 }
 
 static bool xenvif_rx_queue_ready(struct xenvif_queue *queue)
@@ -2038,8 +2036,9 @@ static bool xenvif_have_rx_work(struct xenvif_queue *queue)
 {
 	return (!skb_queue_empty(&queue->rx_queue)
 		&& xenvif_rx_ring_slots_available(queue, XEN_NETBK_RX_SLOTS_MAX))
-		|| xenvif_rx_queue_stalled(queue)
-		|| xenvif_rx_queue_ready(queue)
+		|| (queue->vif->stall_timeout &&
+		    (xenvif_rx_queue_stalled(queue)
+		     || xenvif_rx_queue_ready(queue)))
 		|| kthread_should_stop()
 		|| queue->vif->disabled;
 }
@@ -2092,6 +2091,9 @@ int xenvif_kthread_guest_rx(void *data)
 	struct xenvif_queue *queue = data;
 	struct xenvif *vif = queue->vif;
 
+	if (!vif->stall_timeout)
+		xenvif_queue_carrier_on(queue);
+
 	for (;;) {
 		xenvif_wait_for_rx_work(queue);
 
@@ -2118,10 +2120,12 @@ int xenvif_kthread_guest_rx(void *data)
 		 * while it's probably not responsive, drop the
 		 * carrier so packets are dropped earlier.
 		 */
-		if (xenvif_rx_queue_stalled(queue))
-			xenvif_queue_carrier_off(queue);
-		else if (xenvif_rx_queue_ready(queue))
-			xenvif_queue_carrier_on(queue);
+		if (vif->stall_timeout) {
+			if (xenvif_rx_queue_stalled(queue))
+				xenvif_queue_carrier_off(queue);
+			else if (xenvif_rx_queue_ready(queue))
+				xenvif_queue_carrier_on(queue);
+		}
 
 		/* Queued packets may have foreign pages from other
 		 * domains.  These cannot be queued indefinitely as
@@ -2192,9 +2196,6 @@ static int __init netback_init(void)
 	if (rc)
 		goto failed_init;
 
-	rx_drain_timeout_jiffies = msecs_to_jiffies(rx_drain_timeout_msecs);
-	rx_stall_timeout_jiffies = msecs_to_jiffies(rx_stall_timeout_msecs);
-
 #ifdef CONFIG_DEBUG_FS
 	xen_netback_dbg_root = debugfs_create_dir("xen-netback", NULL);
 	if (IS_ERR_OR_NULL(xen_netback_dbg_root))
diff --git a/drivers/net/xen-netback/xenbus.c b/drivers/net/xen-netback/xenbus.c
index d44cd19..efbaf2a 100644
--- a/drivers/net/xen-netback/xenbus.c
+++ b/drivers/net/xen-netback/xenbus.c
@@ -887,9 +887,15 @@ static int read_xenbus_vif_flags(struct backend_info *be)
 		return -EOPNOTSUPP;
 
 	if (xenbus_scanf(XBT_NIL, dev->otherend,
-			 "feature-rx-notify", "%d", &val) < 0 || val == 0) {
-		xenbus_dev_fatal(dev, -EINVAL, "feature-rx-notify is mandatory");
-		return -EINVAL;
+			 "feature-rx-notify", "%d", &val) < 0)
+		val = 0;
+	if (!val) {
+		/* - Reduce drain timeout to poll more frequently for
+		 *   Rx requests.
+		 * - Disable Rx stall detection.
+		 */
+		be->vif->drain_timeout = msecs_to_jiffies(30);
+		be->vif->stall_timeout = 0;
 	}
 
 	if (xenbus_scanf(XBT_NIL, dev->otherend, "feature-sg",
-- 
1.7.10.4