[PATCH net] xen-netback: Fix handling of skbs requiring too many slots

[PATCH net] xen-netback: Fix handling of skbs requiring too many slots

[Zoltan Kiss]

A recent commit (a02eb4 "xen-netback: worse-case estimate in xenvif_rx_action is
underestimating") capped the slot estimation to MAX_SKB_FRAGS, but that triggers
the next BUG_ON a few lines down, as the packet consumes more slots than
estimated.
This patch introduces full_coalesce on the skb callback buffer, which is used in
start_new_rx_buffer() to decide whether netback needs coalescing more
aggresively. By doing that, no packet should need more than
XEN_NETIF_MAX_TX_SIZE / PAGE_SIZE data slots, as the provided buffers are fully
utilized.

Signed-off-by: Zoltan Kiss <zoltan.kiss@citrix.com>
Cc: Paul Durrant <paul.durrant@citrix.com>
Cc: Wei Liu <wei.liu2@citrix.com>
Cc: Ian Campbell <ian.campbell@citrix.com>
Cc: David Vrabel <david.vrabel@citrix.com>
---
diff --git a/drivers/net/xen-netback/netback.c b/drivers/net/xen-netback/netback.c
index 64ab1d1..65fbcd1 100644
--- a/drivers/net/xen-netback/netback.c
+++ b/drivers/net/xen-netback/netback.c
@@ -163,7 +163,10 @@ bool xenvif_rx_ring_slots_available(struct xenvif *vif, int needed)
  * adding 'size' bytes to a buffer which currently contains 'offset'
  * bytes.
  */
-static bool start_new_rx_buffer(int offset, unsigned long size, int head)
+static bool start_new_rx_buffer(int offset,
+				unsigned long size,
+				int head,
+				bool full_coalesce)
 {
 	/* simple case: we have completely filled the current buffer. */
 	if (offset == MAX_BUFFER_OFFSET)
@@ -175,6 +178,7 @@ static bool start_new_rx_buffer(int offset, unsigned long size, int head)
 	 *     (i)   this frag would fit completely in the next buffer
 	 * and (ii)  there is already some data in the current buffer
 	 * and (iii) this is not the head buffer.
+	 * and (iv)  there is no need to fully utilize the buffers
 	 *
 	 * Where:
 	 * - (i) stops us splitting a frag into two copies
@@ -185,6 +189,8 @@ static bool start_new_rx_buffer(int offset, unsigned long size, int head)
 	 *   by (ii) but is explicitly checked because
 	 *   netfront relies on the first buffer being
 	 *   non-empty and can crash otherwise.
+	 * - (iv) is needed for skbs which can use up more than MAX_SKB_FRAGS
+	 *   slot
 	 *
 	 * This means we will effectively linearise small
 	 * frags but do not needlessly split large buffers
@@ -192,7 +198,10 @@ static bool start_new_rx_buffer(int offset, unsigned long size, int head)
 	 * own buffers as before.
 	 */
 	BUG_ON(size > MAX_BUFFER_OFFSET);
-	if ((offset + size > MAX_BUFFER_OFFSET) && offset && !head)
+	if ((offset + size > MAX_BUFFER_OFFSET) &&
+	    offset &&
+	    !head &&
+	    !full_coalesce)
 		return true;
 
 	return false;
@@ -227,6 +236,13 @@ static struct xenvif_rx_meta *get_next_rx_buffer(struct xenvif *vif,
 	return meta;
 }
 
+struct xenvif_rx_cb {
+	int meta_slots_used;
+	bool full_coalesce;
+};
+
+#define XENVIF_RX_CB(skb) ((struct xenvif_rx_cb *)(skb)->cb)
+
 /*
  * Set up the grant operations for this fragment. If it's a flipping
  * interface, we also set up the unmap request from here.
@@ -261,7 +277,10 @@ static void xenvif_gop_frag_copy(struct xenvif *vif, struct sk_buff *skb,
 		if (bytes > size)
 			bytes = size;
 
-		if (start_new_rx_buffer(npo->copy_off, bytes, *head)) {
+		if (start_new_rx_buffer(npo->copy_off,
+					bytes,
+					*head,
+					XENVIF_RX_CB(skb)->full_coalesce)) {
 			/*
 			 * Netfront requires there to be some data in the head
 			 * buffer.
@@ -541,12 +560,6 @@ static void xenvif_add_frag_responses(struct xenvif *vif, int status,
 	}
 }
 
-struct xenvif_rx_cb {
-	int meta_slots_used;
-};
-
-#define XENVIF_RX_CB(skb) ((struct xenvif_rx_cb *)(skb)->cb)
-
 void xenvif_kick_thread(struct xenvif *vif)
 {
 	wake_up(&vif->wq);
@@ -602,10 +615,14 @@ static void xenvif_rx_action(struct xenvif *vif)
 
 		/* To avoid the estimate becoming too pessimal for some
 		 * frontends that limit posted rx requests, cap the estimate
-		 * at MAX_SKB_FRAGS.
+		 * at MAX_SKB_FRAGS. In this case netback will fully coalesce
+		 * the skb into the provided slots.
 		 */
-		if (max_slots_needed > MAX_SKB_FRAGS)
+		if (max_slots_needed > MAX_SKB_FRAGS) {
 			max_slots_needed = MAX_SKB_FRAGS;
+			XENVIF_RX_CB(skb)->full_coalesce = true;
+		} else
+			XENVIF_RX_CB(skb)->full_coalesce = false;
 
 		/* We may need one more slot for GSO metadata */
 		if (skb_is_gso(skb) &&

RE: [PATCH net] xen-netback: Fix handling of skbs requiring too many slots

[David Laight]

From: netdev-owner@vger.kernel.org
> A recent commit (a02eb4 "xen-netback: worse-case estimate in xenvif_rx_action is
> underestimating") capped the slot estimation to MAX_SKB_FRAGS, but that triggers
> the next BUG_ON a few lines down, as the packet consumes more slots than
> estimated.
> This patch introduces full_coalesce on the skb callback buffer, which is used in
> start_new_rx_buffer() to decide whether netback needs coalescing more
> aggresively. By doing that, no packet should need more than
> XEN_NETIF_MAX_TX_SIZE / PAGE_SIZE data slots, as the provided buffers are fully
> utilized.
...
> -static bool start_new_rx_buffer(int offset, unsigned long size, int head)
> +static bool start_new_rx_buffer(int offset,
> +				unsigned long size,
> +				int head,
> +				bool full_coalesce)

The above is completely incorrect layout ...

...
>  	BUG_ON(size > MAX_BUFFER_OFFSET);
> -	if ((offset + size > MAX_BUFFER_OFFSET) && offset && !head)
> +	if ((offset + size > MAX_BUFFER_OFFSET) &&
> +	    offset &&
> +	    !head &&
> +	    !full_coalesce)
>  		return true;

As is that.

	David

Re: [PATCH net] xen-netback: Fix handling of skbs requiring too many slots

[David Laight]

From: netdev-owner@vger.kernel.org
> A recent commit (a02eb4 "xen-netback: worse-case estimate in xenvif_rx_action is
> underestimating") capped the slot estimation to MAX_SKB_FRAGS, but that triggers
> the next BUG_ON a few lines down, as the packet consumes more slots than
> estimated.
> This patch introduces full_coalesce on the skb callback buffer, which is used in
> start_new_rx_buffer() to decide whether netback needs coalescing more
> aggresively. By doing that, no packet should need more than
> XEN_NETIF_MAX_TX_SIZE / PAGE_SIZE data slots, as the provided buffers are fully
> utilized.
...
> -static bool start_new_rx_buffer(int offset, unsigned long size, int head)
> +static bool start_new_rx_buffer(int offset,
> +				unsigned long size,
> +				int head,
> +				bool full_coalesce)

The above is completely incorrect layout ...

...
>  	BUG_ON(size > MAX_BUFFER_OFFSET);
> -	if ((offset + size > MAX_BUFFER_OFFSET) && offset && !head)
> +	if ((offset + size > MAX_BUFFER_OFFSET) &&
> +	    offset &&
> +	    !head &&
> +	    !full_coalesce)
>  		return true;

As is that.

	David

Re: [PATCH net] xen-netback: Fix handling of skbs requiring too many slots

[Zoltan Kiss]

On 04/06/14 09:50, David Laight wrote:
> From: netdev-owner@vger.kernel.org
>> A recent commit (a02eb4 "xen-netback: worse-case estimate in xenvif_rx_action is
>> underestimating") capped the slot estimation to MAX_SKB_FRAGS, but that triggers
>> the next BUG_ON a few lines down, as the packet consumes more slots than
>> estimated.
>> This patch introduces full_coalesce on the skb callback buffer, which is used in
>> start_new_rx_buffer() to decide whether netback needs coalescing more
>> aggresively. By doing that, no packet should need more than
>> XEN_NETIF_MAX_TX_SIZE / PAGE_SIZE data slots, as the provided buffers are fully
>> utilized.
> ...
>> -static bool start_new_rx_buffer(int offset, unsigned long size, int head)
>> +static bool start_new_rx_buffer(int offset,
>> +				unsigned long size,
>> +				int head,
>> +				bool full_coalesce)
>
> The above is completely incorrect layout ...
Can you elaborate a bit please on "above"?
>
> ...
>>   	BUG_ON(size > MAX_BUFFER_OFFSET);
>> -	if ((offset + size > MAX_BUFFER_OFFSET) && offset && !head)
>> +	if ((offset + size > MAX_BUFFER_OFFSET) &&
>> +	    offset &&
>> +	    !head &&
>> +	    !full_coalesce)
>>   		return true;
>
> As is that.
>
> 	David
>
>
>
> --
> To unsubscribe from this list: send the line "unsubscribe netdev" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>

Re: [PATCH net] xen-netback: Fix handling of skbs requiring too many slots

[Zoltan Kiss]

On 04/06/14 09:50, David Laight wrote:
> From: netdev-owner@vger.kernel.org
>> A recent commit (a02eb4 "xen-netback: worse-case estimate in xenvif_rx_action is
>> underestimating") capped the slot estimation to MAX_SKB_FRAGS, but that triggers
>> the next BUG_ON a few lines down, as the packet consumes more slots than
>> estimated.
>> This patch introduces full_coalesce on the skb callback buffer, which is used in
>> start_new_rx_buffer() to decide whether netback needs coalescing more
>> aggresively. By doing that, no packet should need more than
>> XEN_NETIF_MAX_TX_SIZE / PAGE_SIZE data slots, as the provided buffers are fully
>> utilized.
> ...
>> -static bool start_new_rx_buffer(int offset, unsigned long size, int head)
>> +static bool start_new_rx_buffer(int offset,
>> +				unsigned long size,
>> +				int head,
>> +				bool full_coalesce)
>
> The above is completely incorrect layout ...
Can you elaborate a bit please on "above"?
>
> ...
>>   	BUG_ON(size > MAX_BUFFER_OFFSET);
>> -	if ((offset + size > MAX_BUFFER_OFFSET) && offset && !head)
>> +	if ((offset + size > MAX_BUFFER_OFFSET) &&
>> +	    offset &&
>> +	    !head &&
>> +	    !full_coalesce)
>>   		return true;
>
> As is that.
>
> 	David
>
>
>
> --
> To unsubscribe from this list: send the line "unsubscribe netdev" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>

Re: [PATCH net] xen-netback: Fix handling of skbs requiring too many slots

[annie li]

On 2014/6/3 16:30, Zoltan Kiss wrote:
> A recent commit (a02eb4 "xen-netback: worse-case estimate in xenvif_rx_action is
> underestimating") capped the slot estimation to MAX_SKB_FRAGS, but that triggers
> the next BUG_ON a few lines down, as the packet consumes more slots than
> estimated.
> This patch introduces full_coalesce on the skb callback buffer, which is used in
> start_new_rx_buffer() to decide whether netback needs coalescing more
> aggresively. By doing that, no packet should need more than
> XEN_NETIF_MAX_TX_SIZE / PAGE_SIZE data slots,

(XEN_NETIF_MAX_TX_SIZE+1) / PAGE_SIZE here?

Thanks
Annie
> as the provided buffers are fully
> utilized.
>
> Signed-off-by: Zoltan Kiss <zoltan.kiss@citrix.com>
> Cc: Paul Durrant <paul.durrant@citrix.com>
> Cc: Wei Liu <wei.liu2@citrix.com>
> Cc: Ian Campbell <ian.campbell@citrix.com>
> Cc: David Vrabel <david.vrabel@citrix.com>
> ---
> diff --git a/drivers/net/xen-netback/netback.c b/drivers/net/xen-netback/netback.c
> index 64ab1d1..65fbcd1 100644
> --- a/drivers/net/xen-netback/netback.c
> +++ b/drivers/net/xen-netback/netback.c
> @@ -163,7 +163,10 @@ bool xenvif_rx_ring_slots_available(struct xenvif *vif, int needed)
>    * adding 'size' bytes to a buffer which currently contains 'offset'
>    * bytes.
>    */
> -static bool start_new_rx_buffer(int offset, unsigned long size, int head)
> +static bool start_new_rx_buffer(int offset,
> +				unsigned long size,
> +				int head,
> +				bool full_coalesce)
>   {
>   	/* simple case: we have completely filled the current buffer. */
>   	if (offset == MAX_BUFFER_OFFSET)
> @@ -175,6 +178,7 @@ static bool start_new_rx_buffer(int offset, unsigned long size, int head)
>   	 *     (i)   this frag would fit completely in the next buffer
>   	 * and (ii)  there is already some data in the current buffer
>   	 * and (iii) this is not the head buffer.
> +	 * and (iv)  there is no need to fully utilize the buffers
>   	 *
>   	 * Where:
>   	 * - (i) stops us splitting a frag into two copies
> @@ -185,6 +189,8 @@ static bool start_new_rx_buffer(int offset, unsigned long size, int head)
>   	 *   by (ii) but is explicitly checked because
>   	 *   netfront relies on the first buffer being
>   	 *   non-empty and can crash otherwise.
> +	 * - (iv) is needed for skbs which can use up more than MAX_SKB_FRAGS
> +	 *   slot
>   	 *
>   	 * This means we will effectively linearise small
>   	 * frags but do not needlessly split large buffers
> @@ -192,7 +198,10 @@ static bool start_new_rx_buffer(int offset, unsigned long size, int head)
>   	 * own buffers as before.
>   	 */
>   	BUG_ON(size > MAX_BUFFER_OFFSET);
> -	if ((offset + size > MAX_BUFFER_OFFSET) && offset && !head)
> +	if ((offset + size > MAX_BUFFER_OFFSET) &&
> +	    offset &&
> +	    !head &&
> +	    !full_coalesce)
>   		return true;
>   
>   	return false;
> @@ -227,6 +236,13 @@ static struct xenvif_rx_meta *get_next_rx_buffer(struct xenvif *vif,
>   	return meta;
>   }
>   
> +struct xenvif_rx_cb {
> +	int meta_slots_used;
> +	bool full_coalesce;
> +};
> +
> +#define XENVIF_RX_CB(skb) ((struct xenvif_rx_cb *)(skb)->cb)
> +
>   /*
>    * Set up the grant operations for this fragment. If it's a flipping
>    * interface, we also set up the unmap request from here.
> @@ -261,7 +277,10 @@ static void xenvif_gop_frag_copy(struct xenvif *vif, struct sk_buff *skb,
>   		if (bytes > size)
>   			bytes = size;
>   
> -		if (start_new_rx_buffer(npo->copy_off, bytes, *head)) {
> +		if (start_new_rx_buffer(npo->copy_off,
> +					bytes,
> +					*head,
> +					XENVIF_RX_CB(skb)->full_coalesce)) {
>   			/*
>   			 * Netfront requires there to be some data in the head
>   			 * buffer.
> @@ -541,12 +560,6 @@ static void xenvif_add_frag_responses(struct xenvif *vif, int status,
>   	}
>   }
>   
> -struct xenvif_rx_cb {
> -	int meta_slots_used;
> -};
> -
> -#define XENVIF_RX_CB(skb) ((struct xenvif_rx_cb *)(skb)->cb)
> -
>   void xenvif_kick_thread(struct xenvif *vif)
>   {
>   	wake_up(&vif->wq);
> @@ -602,10 +615,14 @@ static void xenvif_rx_action(struct xenvif *vif)
>   
>   		/* To avoid the estimate becoming too pessimal for some
>   		 * frontends that limit posted rx requests, cap the estimate
> -		 * at MAX_SKB_FRAGS.
> +		 * at MAX_SKB_FRAGS. In this case netback will fully coalesce
> +		 * the skb into the provided slots.
>   		 */
> -		if (max_slots_needed > MAX_SKB_FRAGS)
> +		if (max_slots_needed > MAX_SKB_FRAGS) {
>   			max_slots_needed = MAX_SKB_FRAGS;
> +			XENVIF_RX_CB(skb)->full_coalesce = true;
> +		} else
> +			XENVIF_RX_CB(skb)->full_coalesce = false;

I am not so clear hear, when max_slots_needed > MAX_SKB_FRAGS, then 
full_coalesce is always true.
>   
>   		/* We may need one more slot for GSO metadata */
>   		if (skb_is_gso(skb) &&
>
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@lists.xen.org
> http://lists.xen.org/xen-devel

Re: [Xen-devel] [PATCH net] xen-netback: Fix handling of skbs requiring too many slots

[Zoltan Kiss]

On 04/06/14 16:09, annie li wrote:
>
> On 2014/6/3 16:30, Zoltan Kiss wrote:
>> A recent commit (a02eb4 "xen-netback: worse-case estimate in
>> xenvif_rx_action is
>> underestimating") capped the slot estimation to MAX_SKB_FRAGS, but
>> that triggers
>> the next BUG_ON a few lines down, as the packet consumes more slots than
>> estimated.
>> This patch introduces full_coalesce on the skb callback buffer, which
>> is used in
>> start_new_rx_buffer() to decide whether netback needs coalescing more
>> aggresively. By doing that, no packet should need more than
>> XEN_NETIF_MAX_TX_SIZE / PAGE_SIZE data slots,
>
> (XEN_NETIF_MAX_TX_SIZE+1) / PAGE_SIZE here?

Do you think about the GSO slot? That's why I wrote "data slot", however 
that's probably not a clear terminology. I'll add then that excluding 
GSO slot, as it doesn't carry data directly, therefore it's irrelevant 
from this point of view.

Zoli

Re: [PATCH net] xen-netback: Fix handling of skbs requiring too many slots

[Zoltan Kiss]

On 04/06/14 16:09, annie li wrote:
>
> On 2014/6/3 16:30, Zoltan Kiss wrote:
>> A recent commit (a02eb4 "xen-netback: worse-case estimate in
>> xenvif_rx_action is
>> underestimating") capped the slot estimation to MAX_SKB_FRAGS, but
>> that triggers
>> the next BUG_ON a few lines down, as the packet consumes more slots than
>> estimated.
>> This patch introduces full_coalesce on the skb callback buffer, which
>> is used in
>> start_new_rx_buffer() to decide whether netback needs coalescing more
>> aggresively. By doing that, no packet should need more than
>> XEN_NETIF_MAX_TX_SIZE / PAGE_SIZE data slots,
>
> (XEN_NETIF_MAX_TX_SIZE+1) / PAGE_SIZE here?

Do you think about the GSO slot? That's why I wrote "data slot", however 
that's probably not a clear terminology. I'll add then that excluding 
GSO slot, as it doesn't carry data directly, therefore it's irrelevant 
from this point of view.

Zoli

Re: [PATCH net] xen-netback: Fix handling of skbs requiring too many slots

[Zoltan Kiss]

On 04/06/14 11:15, Zoltan Kiss wrote:
> On 04/06/14 09:50, David Laight wrote:
>> From: netdev-owner@vger.kernel.org
>>> A recent commit (a02eb4 "xen-netback: worse-case estimate in
>>> xenvif_rx_action is
>>> underestimating") capped the slot estimation to MAX_SKB_FRAGS, but
>>> that triggers
>>> the next BUG_ON a few lines down, as the packet consumes more slots than
>>> estimated.
>>> This patch introduces full_coalesce on the skb callback buffer, which
>>> is used in
>>> start_new_rx_buffer() to decide whether netback needs coalescing more
>>> aggresively. By doing that, no packet should need more than
>>> XEN_NETIF_MAX_TX_SIZE / PAGE_SIZE data slots, as the provided buffers
>>> are fully
>>> utilized.
>> ...
>>> -static bool start_new_rx_buffer(int offset, unsigned long size, int
>>> head)
>>> +static bool start_new_rx_buffer(int offset,
>>> +                unsigned long size,
>>> +                int head,
>>> +                bool full_coalesce)
>>
>> The above is completely incorrect layout ...
> Can you elaborate a bit please on "above"?

I just realized you're not talking about skb layout but format. I'll fix 
that.

Zoli

Re: [PATCH net] xen-netback: Fix handling of skbs requiring too many slots

[Zoltan Kiss]

On 04/06/14 11:15, Zoltan Kiss wrote:
> On 04/06/14 09:50, David Laight wrote:
>> From: netdev-owner@vger.kernel.org
>>> A recent commit (a02eb4 "xen-netback: worse-case estimate in
>>> xenvif_rx_action is
>>> underestimating") capped the slot estimation to MAX_SKB_FRAGS, but
>>> that triggers
>>> the next BUG_ON a few lines down, as the packet consumes more slots than
>>> estimated.
>>> This patch introduces full_coalesce on the skb callback buffer, which
>>> is used in
>>> start_new_rx_buffer() to decide whether netback needs coalescing more
>>> aggresively. By doing that, no packet should need more than
>>> XEN_NETIF_MAX_TX_SIZE / PAGE_SIZE data slots, as the provided buffers
>>> are fully
>>> utilized.
>> ...
>>> -static bool start_new_rx_buffer(int offset, unsigned long size, int
>>> head)
>>> +static bool start_new_rx_buffer(int offset,
>>> +                unsigned long size,
>>> +                int head,
>>> +                bool full_coalesce)
>>
>> The above is completely incorrect layout ...
> Can you elaborate a bit please on "above"?

I just realized you're not talking about skb layout but format. I'll fix 
that.

Zoli

Re: [Xen-devel] [PATCH net] xen-netback: Fix handling of skbs requiring too many slots

[annie li]

On 2014/6/4 11:42, Zoltan Kiss wrote:
> On 04/06/14 16:09, annie li wrote:
>>
>> On 2014/6/3 16:30, Zoltan Kiss wrote:
>>> A recent commit (a02eb4 "xen-netback: worse-case estimate in
>>> xenvif_rx_action is
>>> underestimating") capped the slot estimation to MAX_SKB_FRAGS, but
>>> that triggers
>>> the next BUG_ON a few lines down, as the packet consumes more slots 
>>> than
>>> estimated.
>>> This patch introduces full_coalesce on the skb callback buffer, which
>>> is used in
>>> start_new_rx_buffer() to decide whether netback needs coalescing more
>>> aggresively. By doing that, no packet should need more than
>>> XEN_NETIF_MAX_TX_SIZE / PAGE_SIZE data slots,
>>
>> (XEN_NETIF_MAX_TX_SIZE+1) / PAGE_SIZE here?
>
> Do you think about the GSO slot? That's why I wrote "data slot", 
> however that's probably not a clear terminology.

What I mean is: XEN_NETIF_MAX_TX_SIZE is 0xFFFF, and 
XEN_NETIF_MAX_TX_SIZE / PAGE_SIZE turns out to be 15 slots when 
PAGE_SIZE is 4096. You was trying to use XEN_NETIF_MAX_TX_SIZE as max 
size of packet - 64k?

> I'll add then that excluding GSO slot, as it doesn't carry data 
> directly, therefore it's irrelevant from this point of view.

Correct.:-)

Thanks
Annie
>
> Zoli
>
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@lists.xen.org
> http://lists.xen.org/xen-devel

Re: [PATCH net] xen-netback: Fix handling of skbs requiring too many slots

[annie li]

On 2014/6/4 11:42, Zoltan Kiss wrote:
> On 04/06/14 16:09, annie li wrote:
>>
>> On 2014/6/3 16:30, Zoltan Kiss wrote:
>>> A recent commit (a02eb4 "xen-netback: worse-case estimate in
>>> xenvif_rx_action is
>>> underestimating") capped the slot estimation to MAX_SKB_FRAGS, but
>>> that triggers
>>> the next BUG_ON a few lines down, as the packet consumes more slots 
>>> than
>>> estimated.
>>> This patch introduces full_coalesce on the skb callback buffer, which
>>> is used in
>>> start_new_rx_buffer() to decide whether netback needs coalescing more
>>> aggresively. By doing that, no packet should need more than
>>> XEN_NETIF_MAX_TX_SIZE / PAGE_SIZE data slots,
>>
>> (XEN_NETIF_MAX_TX_SIZE+1) / PAGE_SIZE here?
>
> Do you think about the GSO slot? That's why I wrote "data slot", 
> however that's probably not a clear terminology.

What I mean is: XEN_NETIF_MAX_TX_SIZE is 0xFFFF, and 
XEN_NETIF_MAX_TX_SIZE / PAGE_SIZE turns out to be 15 slots when 
PAGE_SIZE is 4096. You was trying to use XEN_NETIF_MAX_TX_SIZE as max 
size of packet - 64k?

> I'll add then that excluding GSO slot, as it doesn't carry data 
> directly, therefore it's irrelevant from this point of view.

Correct.:-)

Thanks
Annie
>
> Zoli
>
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@lists.xen.org
> http://lists.xen.org/xen-devel

Re: [PATCH net] xen-netback: Fix handling of skbs requiring too many slots

[Zoltan Kiss]

Hi,

This patch have made the net and net-next trees already, but not the 
mainline 3.15. That's unfortunate, because just 2 days after someone 
already spotted the problem (see "netback oops in Linux 3.14 / 3.15" on 
xen-devel)
David, should I resend the patch for stable maintaners to include it in 
the 3.15 stable branch?

Regards,

Zoli

On 03/06/14 21:30, Zoltan Kiss wrote:
> A recent commit (a02eb4 "xen-netback: worse-case estimate in xenvif_rx_action is
> underestimating") capped the slot estimation to MAX_SKB_FRAGS, but that triggers
> the next BUG_ON a few lines down, as the packet consumes more slots than
> estimated.
> This patch introduces full_coalesce on the skb callback buffer, which is used in
> start_new_rx_buffer() to decide whether netback needs coalescing more
> aggresively. By doing that, no packet should need more than
> XEN_NETIF_MAX_TX_SIZE / PAGE_SIZE data slots, as the provided buffers are fully
> utilized.
>
> Signed-off-by: Zoltan Kiss <zoltan.kiss@citrix.com>
> Cc: Paul Durrant <paul.durrant@citrix.com>
> Cc: Wei Liu <wei.liu2@citrix.com>
> Cc: Ian Campbell <ian.campbell@citrix.com>
> Cc: David Vrabel <david.vrabel@citrix.com>
> ---
> diff --git a/drivers/net/xen-netback/netback.c b/drivers/net/xen-netback/netback.c
> index 64ab1d1..65fbcd1 100644
> --- a/drivers/net/xen-netback/netback.c
> +++ b/drivers/net/xen-netback/netback.c
> @@ -163,7 +163,10 @@ bool xenvif_rx_ring_slots_available(struct xenvif *vif, int needed)
>    * adding 'size' bytes to a buffer which currently contains 'offset'
>    * bytes.
>    */
> -static bool start_new_rx_buffer(int offset, unsigned long size, int head)
> +static bool start_new_rx_buffer(int offset,
> +				unsigned long size,
> +				int head,
> +				bool full_coalesce)
>   {
>   	/* simple case: we have completely filled the current buffer. */
>   	if (offset == MAX_BUFFER_OFFSET)
> @@ -175,6 +178,7 @@ static bool start_new_rx_buffer(int offset, unsigned long size, int head)
>   	 *     (i)   this frag would fit completely in the next buffer
>   	 * and (ii)  there is already some data in the current buffer
>   	 * and (iii) this is not the head buffer.
> +	 * and (iv)  there is no need to fully utilize the buffers
>   	 *
>   	 * Where:
>   	 * - (i) stops us splitting a frag into two copies
> @@ -185,6 +189,8 @@ static bool start_new_rx_buffer(int offset, unsigned long size, int head)
>   	 *   by (ii) but is explicitly checked because
>   	 *   netfront relies on the first buffer being
>   	 *   non-empty and can crash otherwise.
> +	 * - (iv) is needed for skbs which can use up more than MAX_SKB_FRAGS
> +	 *   slot
>   	 *
>   	 * This means we will effectively linearise small
>   	 * frags but do not needlessly split large buffers
> @@ -192,7 +198,10 @@ static bool start_new_rx_buffer(int offset, unsigned long size, int head)
>   	 * own buffers as before.
>   	 */
>   	BUG_ON(size > MAX_BUFFER_OFFSET);
> -	if ((offset + size > MAX_BUFFER_OFFSET) && offset && !head)
> +	if ((offset + size > MAX_BUFFER_OFFSET) &&
> +	    offset &&
> +	    !head &&
> +	    !full_coalesce)
>   		return true;
>
>   	return false;
> @@ -227,6 +236,13 @@ static struct xenvif_rx_meta *get_next_rx_buffer(struct xenvif *vif,
>   	return meta;
>   }
>
> +struct xenvif_rx_cb {
> +	int meta_slots_used;
> +	bool full_coalesce;
> +};
> +
> +#define XENVIF_RX_CB(skb) ((struct xenvif_rx_cb *)(skb)->cb)
> +
>   /*
>    * Set up the grant operations for this fragment. If it's a flipping
>    * interface, we also set up the unmap request from here.
> @@ -261,7 +277,10 @@ static void xenvif_gop_frag_copy(struct xenvif *vif, struct sk_buff *skb,
>   		if (bytes > size)
>   			bytes = size;
>
> -		if (start_new_rx_buffer(npo->copy_off, bytes, *head)) {
> +		if (start_new_rx_buffer(npo->copy_off,
> +					bytes,
> +					*head,
> +					XENVIF_RX_CB(skb)->full_coalesce)) {
>   			/*
>   			 * Netfront requires there to be some data in the head
>   			 * buffer.
> @@ -541,12 +560,6 @@ static void xenvif_add_frag_responses(struct xenvif *vif, int status,
>   	}
>   }
>
> -struct xenvif_rx_cb {
> -	int meta_slots_used;
> -};
> -
> -#define XENVIF_RX_CB(skb) ((struct xenvif_rx_cb *)(skb)->cb)
> -
>   void xenvif_kick_thread(struct xenvif *vif)
>   {
>   	wake_up(&vif->wq);
> @@ -602,10 +615,14 @@ static void xenvif_rx_action(struct xenvif *vif)
>
>   		/* To avoid the estimate becoming too pessimal for some
>   		 * frontends that limit posted rx requests, cap the estimate
> -		 * at MAX_SKB_FRAGS.
> +		 * at MAX_SKB_FRAGS. In this case netback will fully coalesce
> +		 * the skb into the provided slots.
>   		 */
> -		if (max_slots_needed > MAX_SKB_FRAGS)
> +		if (max_slots_needed > MAX_SKB_FRAGS) {
>   			max_slots_needed = MAX_SKB_FRAGS;
> +			XENVIF_RX_CB(skb)->full_coalesce = true;
> +		} else
> +			XENVIF_RX_CB(skb)->full_coalesce = false;
>
>   		/* We may need one more slot for GSO metadata */
>   		if (skb_is_gso(skb) &&
>

Re: [PATCH net] xen-netback: Fix handling of skbs requiring too many slots

[Zoltan Kiss]

Hi,

This patch have made the net and net-next trees already, but not the 
mainline 3.15. That's unfortunate, because just 2 days after someone 
already spotted the problem (see "netback oops in Linux 3.14 / 3.15" on 
xen-devel)
David, should I resend the patch for stable maintaners to include it in 
the 3.15 stable branch?

Regards,

Zoli

On 03/06/14 21:30, Zoltan Kiss wrote:
> A recent commit (a02eb4 "xen-netback: worse-case estimate in xenvif_rx_action is
> underestimating") capped the slot estimation to MAX_SKB_FRAGS, but that triggers
> the next BUG_ON a few lines down, as the packet consumes more slots than
> estimated.
> This patch introduces full_coalesce on the skb callback buffer, which is used in
> start_new_rx_buffer() to decide whether netback needs coalescing more
> aggresively. By doing that, no packet should need more than
> XEN_NETIF_MAX_TX_SIZE / PAGE_SIZE data slots, as the provided buffers are fully
> utilized.
>
> Signed-off-by: Zoltan Kiss <zoltan.kiss@citrix.com>
> Cc: Paul Durrant <paul.durrant@citrix.com>
> Cc: Wei Liu <wei.liu2@citrix.com>
> Cc: Ian Campbell <ian.campbell@citrix.com>
> Cc: David Vrabel <david.vrabel@citrix.com>
> ---
> diff --git a/drivers/net/xen-netback/netback.c b/drivers/net/xen-netback/netback.c
> index 64ab1d1..65fbcd1 100644
> --- a/drivers/net/xen-netback/netback.c
> +++ b/drivers/net/xen-netback/netback.c
> @@ -163,7 +163,10 @@ bool xenvif_rx_ring_slots_available(struct xenvif *vif, int needed)
>    * adding 'size' bytes to a buffer which currently contains 'offset'
>    * bytes.
>    */
> -static bool start_new_rx_buffer(int offset, unsigned long size, int head)
> +static bool start_new_rx_buffer(int offset,
> +				unsigned long size,
> +				int head,
> +				bool full_coalesce)
>   {
>   	/* simple case: we have completely filled the current buffer. */
>   	if (offset == MAX_BUFFER_OFFSET)
> @@ -175,6 +178,7 @@ static bool start_new_rx_buffer(int offset, unsigned long size, int head)
>   	 *     (i)   this frag would fit completely in the next buffer
>   	 * and (ii)  there is already some data in the current buffer
>   	 * and (iii) this is not the head buffer.
> +	 * and (iv)  there is no need to fully utilize the buffers
>   	 *
>   	 * Where:
>   	 * - (i) stops us splitting a frag into two copies
> @@ -185,6 +189,8 @@ static bool start_new_rx_buffer(int offset, unsigned long size, int head)
>   	 *   by (ii) but is explicitly checked because
>   	 *   netfront relies on the first buffer being
>   	 *   non-empty and can crash otherwise.
> +	 * - (iv) is needed for skbs which can use up more than MAX_SKB_FRAGS
> +	 *   slot
>   	 *
>   	 * This means we will effectively linearise small
>   	 * frags but do not needlessly split large buffers
> @@ -192,7 +198,10 @@ static bool start_new_rx_buffer(int offset, unsigned long size, int head)
>   	 * own buffers as before.
>   	 */
>   	BUG_ON(size > MAX_BUFFER_OFFSET);
> -	if ((offset + size > MAX_BUFFER_OFFSET) && offset && !head)
> +	if ((offset + size > MAX_BUFFER_OFFSET) &&
> +	    offset &&
> +	    !head &&
> +	    !full_coalesce)
>   		return true;
>
>   	return false;
> @@ -227,6 +236,13 @@ static struct xenvif_rx_meta *get_next_rx_buffer(struct xenvif *vif,
>   	return meta;
>   }
>
> +struct xenvif_rx_cb {
> +	int meta_slots_used;
> +	bool full_coalesce;
> +};
> +
> +#define XENVIF_RX_CB(skb) ((struct xenvif_rx_cb *)(skb)->cb)
> +
>   /*
>    * Set up the grant operations for this fragment. If it's a flipping
>    * interface, we also set up the unmap request from here.
> @@ -261,7 +277,10 @@ static void xenvif_gop_frag_copy(struct xenvif *vif, struct sk_buff *skb,
>   		if (bytes > size)
>   			bytes = size;
>
> -		if (start_new_rx_buffer(npo->copy_off, bytes, *head)) {
> +		if (start_new_rx_buffer(npo->copy_off,
> +					bytes,
> +					*head,
> +					XENVIF_RX_CB(skb)->full_coalesce)) {
>   			/*
>   			 * Netfront requires there to be some data in the head
>   			 * buffer.
> @@ -541,12 +560,6 @@ static void xenvif_add_frag_responses(struct xenvif *vif, int status,
>   	}
>   }
>
> -struct xenvif_rx_cb {
> -	int meta_slots_used;
> -};
> -
> -#define XENVIF_RX_CB(skb) ((struct xenvif_rx_cb *)(skb)->cb)
> -
>   void xenvif_kick_thread(struct xenvif *vif)
>   {
>   	wake_up(&vif->wq);
> @@ -602,10 +615,14 @@ static void xenvif_rx_action(struct xenvif *vif)
>
>   		/* To avoid the estimate becoming too pessimal for some
>   		 * frontends that limit posted rx requests, cap the estimate
> -		 * at MAX_SKB_FRAGS.
> +		 * at MAX_SKB_FRAGS. In this case netback will fully coalesce
> +		 * the skb into the provided slots.
>   		 */
> -		if (max_slots_needed > MAX_SKB_FRAGS)
> +		if (max_slots_needed > MAX_SKB_FRAGS) {
>   			max_slots_needed = MAX_SKB_FRAGS;
> +			XENVIF_RX_CB(skb)->full_coalesce = true;
> +		} else
> +			XENVIF_RX_CB(skb)->full_coalesce = false;
>
>   		/* We may need one more slot for GSO metadata */
>   		if (skb_is_gso(skb) &&
>

Re: [PATCH net] xen-netback: Fix handling of skbs requiring too many slots

[David Miller]

From: Zoltan Kiss <zoltan.kiss@citrix.com>
Date: Wed, 11 Jun 2014 13:36:40 +0100

> This patch have made the net and net-next trees already, but not the
> mainline 3.15. That's unfortunate, because just 2 days after someone
> already spotted the problem (see "netback oops in Linux 3.14 / 3.15"
> on xen-devel)
> David, should I resend the patch for stable maintaners to include it
> in the 3.15 stable branch?

Networking patches are submitted to -stable by me, so you have to ask
me explicitly to queue it up.

Note that I do try to let patches "cook" in the networking tree for
some time before I send them off to -stable, this can be up to two
weeks.

Re: [PATCH net] xen-netback: Fix handling of skbs requiring too many slots

[David Miller]

From: Zoltan Kiss <zoltan.kiss@citrix.com>
Date: Wed, 11 Jun 2014 13:36:40 +0100

> This patch have made the net and net-next trees already, but not the
> mainline 3.15. That's unfortunate, because just 2 days after someone
> already spotted the problem (see "netback oops in Linux 3.14 / 3.15"
> on xen-devel)
> David, should I resend the patch for stable maintaners to include it
> in the 3.15 stable branch?

Networking patches are submitted to -stable by me, so you have to ask
me explicitly to queue it up.

Note that I do try to let patches "cook" in the networking tree for
some time before I send them off to -stable, this can be up to two
weeks.

[PATCH net] xen-netback: Fix handling of skbs requiring too many slots

[Zoltan Kiss]

A recent commit (a02eb4 "xen-netback: worse-case estimate in xenvif_rx_action is
underestimating") capped the slot estimation to MAX_SKB_FRAGS, but that triggers
the next BUG_ON a few lines down, as the packet consumes more slots than
estimated.
This patch introduces full_coalesce on the skb callback buffer, which is used in
start_new_rx_buffer() to decide whether netback needs coalescing more
aggresively. By doing that, no packet should need more than
XEN_NETIF_MAX_TX_SIZE / PAGE_SIZE data slots, as the provided buffers are fully
utilized.

Signed-off-by: Zoltan Kiss <zoltan.kiss@citrix.com>
Cc: Paul Durrant <paul.durrant@citrix.com>
Cc: Wei Liu <wei.liu2@citrix.com>
Cc: Ian Campbell <ian.campbell@citrix.com>
Cc: David Vrabel <david.vrabel@citrix.com>
---
diff --git a/drivers/net/xen-netback/netback.c b/drivers/net/xen-netback/netback.c
index 64ab1d1..65fbcd1 100644
--- a/drivers/net/xen-netback/netback.c
+++ b/drivers/net/xen-netback/netback.c
@@ -163,7 +163,10 @@ bool xenvif_rx_ring_slots_available(struct xenvif *vif, int needed)
  * adding 'size' bytes to a buffer which currently contains 'offset'
  * bytes.
  */
-static bool start_new_rx_buffer(int offset, unsigned long size, int head)
+static bool start_new_rx_buffer(int offset,
+				unsigned long size,
+				int head,
+				bool full_coalesce)
 {
 	/* simple case: we have completely filled the current buffer. */
 	if (offset == MAX_BUFFER_OFFSET)
@@ -175,6 +178,7 @@ static bool start_new_rx_buffer(int offset, unsigned long size, int head)
 	 *     (i)   this frag would fit completely in the next buffer
 	 * and (ii)  there is already some data in the current buffer
 	 * and (iii) this is not the head buffer.
+	 * and (iv)  there is no need to fully utilize the buffers
 	 *
 	 * Where:
 	 * - (i) stops us splitting a frag into two copies
@@ -185,6 +189,8 @@ static bool start_new_rx_buffer(int offset, unsigned long size, int head)
 	 *   by (ii) but is explicitly checked because
 	 *   netfront relies on the first buffer being
 	 *   non-empty and can crash otherwise.
+	 * - (iv) is needed for skbs which can use up more than MAX_SKB_FRAGS
+	 *   slot
 	 *
 	 * This means we will effectively linearise small
 	 * frags but do not needlessly split large buffers
@@ -192,7 +198,10 @@ static bool start_new_rx_buffer(int offset, unsigned long size, int head)
 	 * own buffers as before.
 	 */
 	BUG_ON(size > MAX_BUFFER_OFFSET);
-	if ((offset + size > MAX_BUFFER_OFFSET) && offset && !head)
+	if ((offset + size > MAX_BUFFER_OFFSET) &&
+	    offset &&
+	    !head &&
+	    !full_coalesce)
 		return true;
 
 	return false;
@@ -227,6 +236,13 @@ static struct xenvif_rx_meta *get_next_rx_buffer(struct xenvif *vif,
 	return meta;
 }
 
+struct xenvif_rx_cb {
+	int meta_slots_used;
+	bool full_coalesce;
+};
+
+#define XENVIF_RX_CB(skb) ((struct xenvif_rx_cb *)(skb)->cb)
+
 /*
  * Set up the grant operations for this fragment. If it's a flipping
  * interface, we also set up the unmap request from here.
@@ -261,7 +277,10 @@ static void xenvif_gop_frag_copy(struct xenvif *vif, struct sk_buff *skb,
 		if (bytes > size)
 			bytes = size;
 
-		if (start_new_rx_buffer(npo->copy_off, bytes, *head)) {
+		if (start_new_rx_buffer(npo->copy_off,
+					bytes,
+					*head,
+					XENVIF_RX_CB(skb)->full_coalesce)) {
 			/*
 			 * Netfront requires there to be some data in the head
 			 * buffer.
@@ -541,12 +560,6 @@ static void xenvif_add_frag_responses(struct xenvif *vif, int status,
 	}
 }
 
-struct xenvif_rx_cb {
-	int meta_slots_used;
-};
-
-#define XENVIF_RX_CB(skb) ((struct xenvif_rx_cb *)(skb)->cb)
-
 void xenvif_kick_thread(struct xenvif *vif)
 {
 	wake_up(&vif->wq);
@@ -602,10 +615,14 @@ static void xenvif_rx_action(struct xenvif *vif)
 
 		/* To avoid the estimate becoming too pessimal for some
 		 * frontends that limit posted rx requests, cap the estimate
-		 * at MAX_SKB_FRAGS.
+		 * at MAX_SKB_FRAGS. In this case netback will fully coalesce
+		 * the skb into the provided slots.
 		 */
-		if (max_slots_needed > MAX_SKB_FRAGS)
+		if (max_slots_needed > MAX_SKB_FRAGS) {
 			max_slots_needed = MAX_SKB_FRAGS;
+			XENVIF_RX_CB(skb)->full_coalesce = true;
+		} else
+			XENVIF_RX_CB(skb)->full_coalesce = false;
 
 		/* We may need one more slot for GSO metadata */
 		if (skb_is_gso(skb) &&