* RE: [PATCH net] xen-netback: Fix slot estimation
2014-06-03 13:32 [PATCH net] xen-netback: Fix slot estimation Zoltan Kiss
@ 2014-06-03 13:37 ` Paul Durrant
2014-06-03 14:04 ` Zoltan Kiss
2014-06-03 14:04 ` Zoltan Kiss
2014-06-03 13:37 ` Paul Durrant
` (4 subsequent siblings)
5 siblings, 2 replies; 16+ messages in thread
From: Paul Durrant @ 2014-06-03 13:37 UTC (permalink / raw)
To: Zoltan Kiss, xen-devel@lists.xenproject.org, Ian Campbell,
Wei Liu, linux@eikelenboom.it
Cc: netdev@vger.kernel.org, David Vrabel, davem@davemloft.net
> -----Original Message-----
> From: Zoltan Kiss
> Sent: 03 June 2014 14:32
> To: xen-devel@lists.xenproject.org; Ian Campbell; Wei Liu; Paul Durrant;
> linux@eikelenboom.it
> Cc: netdev@vger.kernel.org; David Vrabel; davem@davemloft.net; Zoltan
> Kiss
> Subject: [PATCH net] xen-netback: Fix slot estimation
>
> 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 remove that cap, and if the frontend doesn't provide enough slot,
> put back the skb to the top of the queue and caps rx_last_skb_slots. When
> the
> next try also fails, it drops the packet.
> Capping rx_last_skb_slots is needed because if the frontend never gives
> enough
> slots, the ring gets stalled.
>
> 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 da85ffb..7164157 100644
> --- a/drivers/net/xen-netback/netback.c
> +++ b/drivers/net/xen-netback/netback.c
> @@ -600,13 +600,6 @@ static void xenvif_rx_action(struct xenvif *vif)
> PAGE_SIZE);
> }
>
> - /* To avoid the estimate becoming too pessimal for some
> - * frontends that limit posted rx requests, cap the estimate
> - * at MAX_SKB_FRAGS.
> - */
> - if (max_slots_needed > MAX_SKB_FRAGS)
> - max_slots_needed = MAX_SKB_FRAGS;
> -
> /* We may need one more slot for GSO metadata */
> if (skb_is_gso(skb) &&
> (skb_shinfo(skb)->gso_type & SKB_GSO_TCPV4 ||
> @@ -615,9 +608,27 @@ static void xenvif_rx_action(struct xenvif *vif)
>
> /* If the skb may not fit then bail out now */
> if (!xenvif_rx_ring_slots_available(vif, max_slots_needed)) {
> + /* If the skb needs more than MAX_SKB_FRAGS
> slots, it
> + * can happen that the frontend never gives us
> enough.
> + * To avoid spining on that packet, first we put it back
> + * to the top of the queue, but if the next try fail,
> + * we drop it.
> + */
> + if (max_slots_needed > MAX_SKB_FRAGS &&
> + vif->rx_last_skb_slots == MAX_SKB_FRAGS) {
Isn't it sufficient to say:
if (vif->rx_last_skb_slots != 0)
here? We should not ordinarily wake before the requisite number of slots is available.
Paul
> + kfree_skb(skb);
> + vif->rx_last_skb_slots = 0;
> + continue;
> + }
> skb_queue_head(&vif->rx_queue, skb);
> need_to_notify = true;
> - vif->rx_last_skb_slots = max_slots_needed;
> + /* Cap this otherwise if the guest never gives us
> + * enough slot, rx_work_todo will spin
> + */
> + vif->rx_last_skb_slots =
> + max_slots_needed > MAX_SKB_FRAGS ?
> + MAX_SKB_FRAGS :
> + max_slots_needed;
> break;
> } else
> vif->rx_last_skb_slots = 0;
^ permalink raw reply [flat|nested] 16+ messages in thread* Re: [PATCH net] xen-netback: Fix slot estimation
2014-06-03 13:37 ` Paul Durrant
@ 2014-06-03 14:04 ` Zoltan Kiss
2014-06-03 14:04 ` Zoltan Kiss
1 sibling, 0 replies; 16+ messages in thread
From: Zoltan Kiss @ 2014-06-03 14:04 UTC (permalink / raw)
To: Paul Durrant, xen-devel@lists.xenproject.org, Ian Campbell,
Wei Liu, linux@eikelenboom.it
Cc: netdev@vger.kernel.org, David Vrabel, davem@davemloft.net
On 03/06/14 14:37, Paul Durrant wrote:
>> -----Original Message-----
>> From: Zoltan Kiss
>> Sent: 03 June 2014 14:32
>> To: xen-devel@lists.xenproject.org; Ian Campbell; Wei Liu; Paul Durrant;
>> linux@eikelenboom.it
>> Cc: netdev@vger.kernel.org; David Vrabel; davem@davemloft.net; Zoltan
>> Kiss
>> Subject: [PATCH net] xen-netback: Fix slot estimation
>>
>> 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 remove that cap, and if the frontend doesn't provide enough slot,
>> put back the skb to the top of the queue and caps rx_last_skb_slots. When
>> the
>> next try also fails, it drops the packet.
>> Capping rx_last_skb_slots is needed because if the frontend never gives
>> enough
>> slots, the ring gets stalled.
>>
>> 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 da85ffb..7164157 100644
>> --- a/drivers/net/xen-netback/netback.c
>> +++ b/drivers/net/xen-netback/netback.c
>> @@ -600,13 +600,6 @@ static void xenvif_rx_action(struct xenvif *vif)
>> PAGE_SIZE);
>> }
>>
>> - /* To avoid the estimate becoming too pessimal for some
>> - * frontends that limit posted rx requests, cap the estimate
>> - * at MAX_SKB_FRAGS.
>> - */
>> - if (max_slots_needed > MAX_SKB_FRAGS)
>> - max_slots_needed = MAX_SKB_FRAGS;
>> -
>> /* We may need one more slot for GSO metadata */
>> if (skb_is_gso(skb) &&
>> (skb_shinfo(skb)->gso_type & SKB_GSO_TCPV4 ||
>> @@ -615,9 +608,27 @@ static void xenvif_rx_action(struct xenvif *vif)
>>
>> /* If the skb may not fit then bail out now */
>> if (!xenvif_rx_ring_slots_available(vif, max_slots_needed)) {
>> + /* If the skb needs more than MAX_SKB_FRAGS
>> slots, it
>> + * can happen that the frontend never gives us
>> enough.
>> + * To avoid spining on that packet, first we put it back
>> + * to the top of the queue, but if the next try fail,
>> + * we drop it.
>> + */
>> + if (max_slots_needed > MAX_SKB_FRAGS &&
>> + vif->rx_last_skb_slots == MAX_SKB_FRAGS) {
>
> Isn't it sufficient to say:
>
> if (vif->rx_last_skb_slots != 0)
>
> here? We should not ordinarily wake before the requisite number of slots is available.
Yep, that would be enough
>
> Paul
>
>> + kfree_skb(skb);
>> + vif->rx_last_skb_slots = 0;
>> + continue;
>> + }
>> skb_queue_head(&vif->rx_queue, skb);
>> need_to_notify = true;
>> - vif->rx_last_skb_slots = max_slots_needed;
>> + /* Cap this otherwise if the guest never gives us
>> + * enough slot, rx_work_todo will spin
>> + */
>> + vif->rx_last_skb_slots =
>> + max_slots_needed > MAX_SKB_FRAGS ?
>> + MAX_SKB_FRAGS :
>> + max_slots_needed;
>> break;
>> } else
>> vif->rx_last_skb_slots = 0;
^ permalink raw reply [flat|nested] 16+ messages in thread* Re: [PATCH net] xen-netback: Fix slot estimation
2014-06-03 13:37 ` Paul Durrant
2014-06-03 14:04 ` Zoltan Kiss
@ 2014-06-03 14:04 ` Zoltan Kiss
1 sibling, 0 replies; 16+ messages in thread
From: Zoltan Kiss @ 2014-06-03 14:04 UTC (permalink / raw)
To: Paul Durrant, xen-devel@lists.xenproject.org, Ian Campbell,
Wei Liu, linux@eikelenboom.it
Cc: netdev@vger.kernel.org, David Vrabel, davem@davemloft.net
On 03/06/14 14:37, Paul Durrant wrote:
>> -----Original Message-----
>> From: Zoltan Kiss
>> Sent: 03 June 2014 14:32
>> To: xen-devel@lists.xenproject.org; Ian Campbell; Wei Liu; Paul Durrant;
>> linux@eikelenboom.it
>> Cc: netdev@vger.kernel.org; David Vrabel; davem@davemloft.net; Zoltan
>> Kiss
>> Subject: [PATCH net] xen-netback: Fix slot estimation
>>
>> 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 remove that cap, and if the frontend doesn't provide enough slot,
>> put back the skb to the top of the queue and caps rx_last_skb_slots. When
>> the
>> next try also fails, it drops the packet.
>> Capping rx_last_skb_slots is needed because if the frontend never gives
>> enough
>> slots, the ring gets stalled.
>>
>> 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 da85ffb..7164157 100644
>> --- a/drivers/net/xen-netback/netback.c
>> +++ b/drivers/net/xen-netback/netback.c
>> @@ -600,13 +600,6 @@ static void xenvif_rx_action(struct xenvif *vif)
>> PAGE_SIZE);
>> }
>>
>> - /* To avoid the estimate becoming too pessimal for some
>> - * frontends that limit posted rx requests, cap the estimate
>> - * at MAX_SKB_FRAGS.
>> - */
>> - if (max_slots_needed > MAX_SKB_FRAGS)
>> - max_slots_needed = MAX_SKB_FRAGS;
>> -
>> /* We may need one more slot for GSO metadata */
>> if (skb_is_gso(skb) &&
>> (skb_shinfo(skb)->gso_type & SKB_GSO_TCPV4 ||
>> @@ -615,9 +608,27 @@ static void xenvif_rx_action(struct xenvif *vif)
>>
>> /* If the skb may not fit then bail out now */
>> if (!xenvif_rx_ring_slots_available(vif, max_slots_needed)) {
>> + /* If the skb needs more than MAX_SKB_FRAGS
>> slots, it
>> + * can happen that the frontend never gives us
>> enough.
>> + * To avoid spining on that packet, first we put it back
>> + * to the top of the queue, but if the next try fail,
>> + * we drop it.
>> + */
>> + if (max_slots_needed > MAX_SKB_FRAGS &&
>> + vif->rx_last_skb_slots == MAX_SKB_FRAGS) {
>
> Isn't it sufficient to say:
>
> if (vif->rx_last_skb_slots != 0)
>
> here? We should not ordinarily wake before the requisite number of slots is available.
Yep, that would be enough
>
> Paul
>
>> + kfree_skb(skb);
>> + vif->rx_last_skb_slots = 0;
>> + continue;
>> + }
>> skb_queue_head(&vif->rx_queue, skb);
>> need_to_notify = true;
>> - vif->rx_last_skb_slots = max_slots_needed;
>> + /* Cap this otherwise if the guest never gives us
>> + * enough slot, rx_work_todo will spin
>> + */
>> + vif->rx_last_skb_slots =
>> + max_slots_needed > MAX_SKB_FRAGS ?
>> + MAX_SKB_FRAGS :
>> + max_slots_needed;
>> break;
>> } else
>> vif->rx_last_skb_slots = 0;
^ permalink raw reply [flat|nested] 16+ messages in thread
* Re: [PATCH net] xen-netback: Fix slot estimation
2014-06-03 13:32 [PATCH net] xen-netback: Fix slot estimation Zoltan Kiss
2014-06-03 13:37 ` Paul Durrant
@ 2014-06-03 13:37 ` Paul Durrant
2014-06-03 13:52 ` David Laight
` (3 subsequent siblings)
5 siblings, 0 replies; 16+ messages in thread
From: Paul Durrant @ 2014-06-03 13:37 UTC (permalink / raw)
To: Zoltan Kiss, xen-devel@lists.xenproject.org, Ian Campbell,
Wei Liu, linux@eikelenboom.it
Cc: netdev@vger.kernel.org, David Vrabel, davem@davemloft.net
> -----Original Message-----
> From: Zoltan Kiss
> Sent: 03 June 2014 14:32
> To: xen-devel@lists.xenproject.org; Ian Campbell; Wei Liu; Paul Durrant;
> linux@eikelenboom.it
> Cc: netdev@vger.kernel.org; David Vrabel; davem@davemloft.net; Zoltan
> Kiss
> Subject: [PATCH net] xen-netback: Fix slot estimation
>
> 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 remove that cap, and if the frontend doesn't provide enough slot,
> put back the skb to the top of the queue and caps rx_last_skb_slots. When
> the
> next try also fails, it drops the packet.
> Capping rx_last_skb_slots is needed because if the frontend never gives
> enough
> slots, the ring gets stalled.
>
> 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 da85ffb..7164157 100644
> --- a/drivers/net/xen-netback/netback.c
> +++ b/drivers/net/xen-netback/netback.c
> @@ -600,13 +600,6 @@ static void xenvif_rx_action(struct xenvif *vif)
> PAGE_SIZE);
> }
>
> - /* To avoid the estimate becoming too pessimal for some
> - * frontends that limit posted rx requests, cap the estimate
> - * at MAX_SKB_FRAGS.
> - */
> - if (max_slots_needed > MAX_SKB_FRAGS)
> - max_slots_needed = MAX_SKB_FRAGS;
> -
> /* We may need one more slot for GSO metadata */
> if (skb_is_gso(skb) &&
> (skb_shinfo(skb)->gso_type & SKB_GSO_TCPV4 ||
> @@ -615,9 +608,27 @@ static void xenvif_rx_action(struct xenvif *vif)
>
> /* If the skb may not fit then bail out now */
> if (!xenvif_rx_ring_slots_available(vif, max_slots_needed)) {
> + /* If the skb needs more than MAX_SKB_FRAGS
> slots, it
> + * can happen that the frontend never gives us
> enough.
> + * To avoid spining on that packet, first we put it back
> + * to the top of the queue, but if the next try fail,
> + * we drop it.
> + */
> + if (max_slots_needed > MAX_SKB_FRAGS &&
> + vif->rx_last_skb_slots == MAX_SKB_FRAGS) {
Isn't it sufficient to say:
if (vif->rx_last_skb_slots != 0)
here? We should not ordinarily wake before the requisite number of slots is available.
Paul
> + kfree_skb(skb);
> + vif->rx_last_skb_slots = 0;
> + continue;
> + }
> skb_queue_head(&vif->rx_queue, skb);
> need_to_notify = true;
> - vif->rx_last_skb_slots = max_slots_needed;
> + /* Cap this otherwise if the guest never gives us
> + * enough slot, rx_work_todo will spin
> + */
> + vif->rx_last_skb_slots =
> + max_slots_needed > MAX_SKB_FRAGS ?
> + MAX_SKB_FRAGS :
> + max_slots_needed;
> break;
> } else
> vif->rx_last_skb_slots = 0;
^ permalink raw reply [flat|nested] 16+ messages in thread* RE: [PATCH net] xen-netback: Fix slot estimation
2014-06-03 13:32 [PATCH net] xen-netback: Fix slot estimation Zoltan Kiss
2014-06-03 13:37 ` Paul Durrant
2014-06-03 13:37 ` Paul Durrant
@ 2014-06-03 13:52 ` David Laight
2014-06-03 20:24 ` Zoltan Kiss
2014-06-03 20:24 ` Zoltan Kiss
2014-06-03 13:52 ` David Laight
` (2 subsequent siblings)
5 siblings, 2 replies; 16+ messages in thread
From: David Laight @ 2014-06-03 13:52 UTC (permalink / raw)
To: 'Zoltan Kiss', xen-devel@lists.xenproject.org,
ian.campbell@citrix.com, wei.liu2@citrix.com,
paul.durrant@citrix.com, linux@eikelenboom.it
Cc: netdev@vger.kernel.org, david.vrabel@citrix.com,
davem@davemloft.net
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 remove that cap, and if the frontend doesn't provide enough slot,
> put back the skb to the top of the queue and caps rx_last_skb_slots. When the
> next try also fails, it drops the packet.
> Capping rx_last_skb_slots is needed because if the frontend never gives enough
> slots, the ring gets stalled.
>
> 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 da85ffb..7164157 100644
> --- a/drivers/net/xen-netback/netback.c
> +++ b/drivers/net/xen-netback/netback.c
> @@ -600,13 +600,6 @@ static void xenvif_rx_action(struct xenvif *vif)
> PAGE_SIZE);
> }
>
> - /* To avoid the estimate becoming too pessimal for some
> - * frontends that limit posted rx requests, cap the estimate
> - * at MAX_SKB_FRAGS.
> - */
> - if (max_slots_needed > MAX_SKB_FRAGS)
> - max_slots_needed = MAX_SKB_FRAGS;
> -
> /* We may need one more slot for GSO metadata */
> if (skb_is_gso(skb) &&
> (skb_shinfo(skb)->gso_type & SKB_GSO_TCPV4 ||
> @@ -615,9 +608,27 @@ static void xenvif_rx_action(struct xenvif *vif)
>
> /* If the skb may not fit then bail out now */
> if (!xenvif_rx_ring_slots_available(vif, max_slots_needed)) {
> + /* If the skb needs more than MAX_SKB_FRAGS slots, it
> + * can happen that the frontend never gives us enough.
> + * To avoid spining on that packet, first we put it back
> + * to the top of the queue, but if the next try fail,
> + * we drop it.
> + */
> + if (max_slots_needed > MAX_SKB_FRAGS &&
> + vif->rx_last_skb_slots == MAX_SKB_FRAGS) {
> + kfree_skb(skb);
> + vif->rx_last_skb_slots = 0;
> + continue;
> + }
A silent discard here doesn't seem right at all.
While it stops the kernel crashing, or the entire interface locking
up; it is likely to leave one connection 'stuck' - a TCP retransmission
is likely to include the same fragments.
>From a user point of view this as almost as bad.
David
> skb_queue_head(&vif->rx_queue, skb);
> need_to_notify = true;
> - vif->rx_last_skb_slots = max_slots_needed;
> + /* Cap this otherwise if the guest never gives us
> + * enough slot, rx_work_todo will spin
> + */
> + vif->rx_last_skb_slots =
> + max_slots_needed > MAX_SKB_FRAGS ?
> + MAX_SKB_FRAGS :
> + max_slots_needed;
> break;
> } else
> vif->rx_last_skb_slots = 0;
> --
> 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
^ permalink raw reply [flat|nested] 16+ messages in thread* Re: [PATCH net] xen-netback: Fix slot estimation
2014-06-03 13:52 ` David Laight
@ 2014-06-03 20:24 ` Zoltan Kiss
2014-06-03 20:24 ` Zoltan Kiss
1 sibling, 0 replies; 16+ messages in thread
From: Zoltan Kiss @ 2014-06-03 20:24 UTC (permalink / raw)
To: David Laight, xen-devel@lists.xenproject.org,
ian.campbell@citrix.com, wei.liu2@citrix.com,
paul.durrant@citrix.com, linux@eikelenboom.it
Cc: netdev@vger.kernel.org, david.vrabel@citrix.com,
davem@davemloft.net
On 03/06/14 14:52, David Laight wrote:
> From: netdev-owner@vger.kernel.org
>> @@ -615,9 +608,27 @@ static void xenvif_rx_action(struct xenvif *vif)
>>
>> /* If the skb may not fit then bail out now */
>> if (!xenvif_rx_ring_slots_available(vif, max_slots_needed)) {
>> + /* If the skb needs more than MAX_SKB_FRAGS slots, it
>> + * can happen that the frontend never gives us enough.
>> + * To avoid spining on that packet, first we put it back
>> + * to the top of the queue, but if the next try fail,
>> + * we drop it.
>> + */
>> + if (max_slots_needed > MAX_SKB_FRAGS &&
>> + vif->rx_last_skb_slots == MAX_SKB_FRAGS) {
>> + kfree_skb(skb);
>> + vif->rx_last_skb_slots = 0;
>> + continue;
>> + }
>
> A silent discard here doesn't seem right at all.
> While it stops the kernel crashing, or the entire interface locking
> up; it is likely to leave one connection 'stuck' - a TCP retransmission
> is likely to include the same fragments.
> From a user point of view this as almost as bad.
Yes, we are aware of this problem for a while. However I have an idea to
solve that in a way that we don't lose performance, and these packets
can pass through as well. See my patch called "Fix handling of skbs
requiring too many slots"
Zoli
^ permalink raw reply [flat|nested] 16+ messages in thread* Re: [PATCH net] xen-netback: Fix slot estimation
2014-06-03 13:52 ` David Laight
2014-06-03 20:24 ` Zoltan Kiss
@ 2014-06-03 20:24 ` Zoltan Kiss
1 sibling, 0 replies; 16+ messages in thread
From: Zoltan Kiss @ 2014-06-03 20:24 UTC (permalink / raw)
To: David Laight, xen-devel@lists.xenproject.org,
ian.campbell@citrix.com, wei.liu2@citrix.com,
paul.durrant@citrix.com, linux@eikelenboom.it
Cc: netdev@vger.kernel.org, david.vrabel@citrix.com,
davem@davemloft.net
On 03/06/14 14:52, David Laight wrote:
> From: netdev-owner@vger.kernel.org
>> @@ -615,9 +608,27 @@ static void xenvif_rx_action(struct xenvif *vif)
>>
>> /* If the skb may not fit then bail out now */
>> if (!xenvif_rx_ring_slots_available(vif, max_slots_needed)) {
>> + /* If the skb needs more than MAX_SKB_FRAGS slots, it
>> + * can happen that the frontend never gives us enough.
>> + * To avoid spining on that packet, first we put it back
>> + * to the top of the queue, but if the next try fail,
>> + * we drop it.
>> + */
>> + if (max_slots_needed > MAX_SKB_FRAGS &&
>> + vif->rx_last_skb_slots == MAX_SKB_FRAGS) {
>> + kfree_skb(skb);
>> + vif->rx_last_skb_slots = 0;
>> + continue;
>> + }
>
> A silent discard here doesn't seem right at all.
> While it stops the kernel crashing, or the entire interface locking
> up; it is likely to leave one connection 'stuck' - a TCP retransmission
> is likely to include the same fragments.
> From a user point of view this as almost as bad.
Yes, we are aware of this problem for a while. However I have an idea to
solve that in a way that we don't lose performance, and these packets
can pass through as well. See my patch called "Fix handling of skbs
requiring too many slots"
Zoli
^ permalink raw reply [flat|nested] 16+ messages in thread
* Re: [PATCH net] xen-netback: Fix slot estimation
2014-06-03 13:32 [PATCH net] xen-netback: Fix slot estimation Zoltan Kiss
` (2 preceding siblings ...)
2014-06-03 13:52 ` David Laight
@ 2014-06-03 13:52 ` David Laight
2014-06-05 22:02 ` David Miller
2014-06-05 22:02 ` David Miller
5 siblings, 0 replies; 16+ messages in thread
From: David Laight @ 2014-06-03 13:52 UTC (permalink / raw)
To: 'Zoltan Kiss', xen-devel@lists.xenproject.org,
ian.campbell@citrix.com, wei.liu2@citrix.com,
paul.durrant@citrix.com, linux@eikelenboom.it
Cc: netdev@vger.kernel.org, david.vrabel@citrix.com,
davem@davemloft.net
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 remove that cap, and if the frontend doesn't provide enough slot,
> put back the skb to the top of the queue and caps rx_last_skb_slots. When the
> next try also fails, it drops the packet.
> Capping rx_last_skb_slots is needed because if the frontend never gives enough
> slots, the ring gets stalled.
>
> 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 da85ffb..7164157 100644
> --- a/drivers/net/xen-netback/netback.c
> +++ b/drivers/net/xen-netback/netback.c
> @@ -600,13 +600,6 @@ static void xenvif_rx_action(struct xenvif *vif)
> PAGE_SIZE);
> }
>
> - /* To avoid the estimate becoming too pessimal for some
> - * frontends that limit posted rx requests, cap the estimate
> - * at MAX_SKB_FRAGS.
> - */
> - if (max_slots_needed > MAX_SKB_FRAGS)
> - max_slots_needed = MAX_SKB_FRAGS;
> -
> /* We may need one more slot for GSO metadata */
> if (skb_is_gso(skb) &&
> (skb_shinfo(skb)->gso_type & SKB_GSO_TCPV4 ||
> @@ -615,9 +608,27 @@ static void xenvif_rx_action(struct xenvif *vif)
>
> /* If the skb may not fit then bail out now */
> if (!xenvif_rx_ring_slots_available(vif, max_slots_needed)) {
> + /* If the skb needs more than MAX_SKB_FRAGS slots, it
> + * can happen that the frontend never gives us enough.
> + * To avoid spining on that packet, first we put it back
> + * to the top of the queue, but if the next try fail,
> + * we drop it.
> + */
> + if (max_slots_needed > MAX_SKB_FRAGS &&
> + vif->rx_last_skb_slots == MAX_SKB_FRAGS) {
> + kfree_skb(skb);
> + vif->rx_last_skb_slots = 0;
> + continue;
> + }
A silent discard here doesn't seem right at all.
While it stops the kernel crashing, or the entire interface locking
up; it is likely to leave one connection 'stuck' - a TCP retransmission
is likely to include the same fragments.
>From a user point of view this as almost as bad.
David
> skb_queue_head(&vif->rx_queue, skb);
> need_to_notify = true;
> - vif->rx_last_skb_slots = max_slots_needed;
> + /* Cap this otherwise if the guest never gives us
> + * enough slot, rx_work_todo will spin
> + */
> + vif->rx_last_skb_slots =
> + max_slots_needed > MAX_SKB_FRAGS ?
> + MAX_SKB_FRAGS :
> + max_slots_needed;
> break;
> } else
> vif->rx_last_skb_slots = 0;
> --
> 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
^ permalink raw reply [flat|nested] 16+ messages in thread* Re: [PATCH net] xen-netback: Fix slot estimation
2014-06-03 13:32 [PATCH net] xen-netback: Fix slot estimation Zoltan Kiss
` (3 preceding siblings ...)
2014-06-03 13:52 ` David Laight
@ 2014-06-05 22:02 ` David Miller
2014-06-05 22:02 ` David Miller
5 siblings, 0 replies; 16+ messages in thread
From: David Miller @ 2014-06-05 22:02 UTC (permalink / raw)
To: zoltan.kiss
Cc: wei.liu2, ian.campbell, netdev, linux, paul.durrant, david.vrabel,
xen-devel
From: Zoltan Kiss <zoltan.kiss@citrix.com>
Date: Tue, 3 Jun 2014 14:32:16 +0100
> 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 remove that cap, and if the frontend doesn't provide enough slot,
> put back the skb to the top of the queue and caps rx_last_skb_slots. When the
> next try also fails, it drops the packet.
> Capping rx_last_skb_slots is needed because if the frontend never gives enough
> slots, the ring gets stalled.
>
> Signed-off-by: Zoltan Kiss <zoltan.kiss@citrix.com>
Like David Laight, I do not like this patch at all.
Yes a crash or BUG_ON triggered is bad, but fixing it by deadlocking
TCP connections (a silent failure) is not an improvement.
I'm not applying this, sorry.
^ permalink raw reply [flat|nested] 16+ messages in thread* Re: [PATCH net] xen-netback: Fix slot estimation
2014-06-03 13:32 [PATCH net] xen-netback: Fix slot estimation Zoltan Kiss
` (4 preceding siblings ...)
2014-06-05 22:02 ` David Miller
@ 2014-06-05 22:02 ` David Miller
2014-06-06 10:20 ` Zoltan Kiss
2014-06-06 10:20 ` Zoltan Kiss
5 siblings, 2 replies; 16+ messages in thread
From: David Miller @ 2014-06-05 22:02 UTC (permalink / raw)
To: zoltan.kiss
Cc: xen-devel, ian.campbell, wei.liu2, paul.durrant, linux, netdev,
david.vrabel
From: Zoltan Kiss <zoltan.kiss@citrix.com>
Date: Tue, 3 Jun 2014 14:32:16 +0100
> 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 remove that cap, and if the frontend doesn't provide enough slot,
> put back the skb to the top of the queue and caps rx_last_skb_slots. When the
> next try also fails, it drops the packet.
> Capping rx_last_skb_slots is needed because if the frontend never gives enough
> slots, the ring gets stalled.
>
> Signed-off-by: Zoltan Kiss <zoltan.kiss@citrix.com>
Like David Laight, I do not like this patch at all.
Yes a crash or BUG_ON triggered is bad, but fixing it by deadlocking
TCP connections (a silent failure) is not an improvement.
I'm not applying this, sorry.
^ permalink raw reply [flat|nested] 16+ messages in thread* Re: [PATCH net] xen-netback: Fix slot estimation
2014-06-05 22:02 ` David Miller
@ 2014-06-06 10:20 ` Zoltan Kiss
2014-06-06 20:06 ` David Miller
2014-06-06 20:06 ` David Miller
2014-06-06 10:20 ` Zoltan Kiss
1 sibling, 2 replies; 16+ messages in thread
From: Zoltan Kiss @ 2014-06-06 10:20 UTC (permalink / raw)
To: David Miller
Cc: xen-devel, ian.campbell, wei.liu2, paul.durrant, linux, netdev,
david.vrabel
On 05/06/14 23:02, David Miller wrote:
> From: Zoltan Kiss<zoltan.kiss@citrix.com>
> Date: Tue, 3 Jun 2014 14:32:16 +0100
>
>> 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 remove that cap, and if the frontend doesn't provide enough slot,
>> put back the skb to the top of the queue and caps rx_last_skb_slots. When the
>> next try also fails, it drops the packet.
>> Capping rx_last_skb_slots is needed because if the frontend never gives enough
>> slots, the ring gets stalled.
>>
>> Signed-off-by: Zoltan Kiss<zoltan.kiss@citrix.com>
> Like David Laight, I do not like this patch at all.
>
> Yes a crash or BUG_ON triggered is bad, but fixing it by deadlocking
> TCP connections (a silent failure) is not an improvement.
>
> I'm not applying this, sorry.
>
Hi,
I haven't wrote it explicitly, but my other patch "xen-netback: Fix
handling of skbs requiring too many slots" supersedes this one.
^ permalink raw reply [flat|nested] 16+ messages in thread
* Re: [PATCH net] xen-netback: Fix slot estimation
2014-06-06 10:20 ` Zoltan Kiss
@ 2014-06-06 20:06 ` David Miller
2014-06-06 20:06 ` David Miller
1 sibling, 0 replies; 16+ messages in thread
From: David Miller @ 2014-06-06 20:06 UTC (permalink / raw)
To: zoltan.kiss
Cc: wei.liu2, ian.campbell, netdev, linux, paul.durrant, david.vrabel,
xen-devel
From: Zoltan Kiss <zoltan.kiss@schaman.hu>
Date: Fri, 06 Jun 2014 11:20:45 +0100
> I haven't wrote it explicitly, but my other patch "xen-netback: Fix
> handling of skbs requiring too many slots" supersedes this one.
Right, I figured this out after reading these threads over again.
^ permalink raw reply [flat|nested] 16+ messages in thread
* Re: [PATCH net] xen-netback: Fix slot estimation
2014-06-06 10:20 ` Zoltan Kiss
2014-06-06 20:06 ` David Miller
@ 2014-06-06 20:06 ` David Miller
1 sibling, 0 replies; 16+ messages in thread
From: David Miller @ 2014-06-06 20:06 UTC (permalink / raw)
To: zoltan.kiss
Cc: xen-devel, ian.campbell, wei.liu2, paul.durrant, linux, netdev,
david.vrabel
From: Zoltan Kiss <zoltan.kiss@schaman.hu>
Date: Fri, 06 Jun 2014 11:20:45 +0100
> I haven't wrote it explicitly, but my other patch "xen-netback: Fix
> handling of skbs requiring too many slots" supersedes this one.
Right, I figured this out after reading these threads over again.
^ permalink raw reply [flat|nested] 16+ messages in thread
* Re: [PATCH net] xen-netback: Fix slot estimation
2014-06-05 22:02 ` David Miller
2014-06-06 10:20 ` Zoltan Kiss
@ 2014-06-06 10:20 ` Zoltan Kiss
1 sibling, 0 replies; 16+ messages in thread
From: Zoltan Kiss @ 2014-06-06 10:20 UTC (permalink / raw)
To: David Miller
Cc: wei.liu2, ian.campbell, netdev, linux, paul.durrant, david.vrabel,
xen-devel
On 05/06/14 23:02, David Miller wrote:
> From: Zoltan Kiss<zoltan.kiss@citrix.com>
> Date: Tue, 3 Jun 2014 14:32:16 +0100
>
>> 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 remove that cap, and if the frontend doesn't provide enough slot,
>> put back the skb to the top of the queue and caps rx_last_skb_slots. When the
>> next try also fails, it drops the packet.
>> Capping rx_last_skb_slots is needed because if the frontend never gives enough
>> slots, the ring gets stalled.
>>
>> Signed-off-by: Zoltan Kiss<zoltan.kiss@citrix.com>
> Like David Laight, I do not like this patch at all.
>
> Yes a crash or BUG_ON triggered is bad, but fixing it by deadlocking
> TCP connections (a silent failure) is not an improvement.
>
> I'm not applying this, sorry.
>
Hi,
I haven't wrote it explicitly, but my other patch "xen-netback: Fix
handling of skbs requiring too many slots" supersedes this one.
^ permalink raw reply [flat|nested] 16+ messages in thread