* [Discussion] About over-MTU-sized skb in virtualized env
@ 2014-12-03 5:40 Du, Fan
0 siblings, 0 replies; 3+ messages in thread
From: Du, Fan @ 2014-12-03 5:40 UTC (permalink / raw
To: fw-HFFVJYpyMKqzQB+pC5nmwQ@public.gmane.org
Cc: dev-yBygre7rU0TnMu66kgdUjQ@public.gmane.org, Du, Fan,
Michael S. Tsirkin,
netdev-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Flavio Leitner,
David Miller
Hi Florian
214 static int ip_finish_output_gso(struct sk_buff *skb)
215 {
216 netdev_features_t features;
217 struct sk_buff *segs;
218 int ret = 0;
219
220 /* common case: locally created skb or seglen is <= mtu */
221 if (((IPCB(skb)->flags & IPSKB_FORWARDED) == 0) ||
222 skb_gso_network_seglen(skb) <= ip_skb_dst_mtu(skb))
223 return ip_finish_output2(skb);
Could you please state _concrete_ _reason_ why locally created skb length is ＿always＿ fitting into MTU size?
Especially in below scenario:
http://docs.openstack.org/admin-guide-cloud/content/figures/14/a/a/common/figures/under-the-hood-scenario-1-ovs-compute.png
As many people have discuss it in this thread:
http://marc.info/?t=141715669700004&r=1&w=2
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^ permalink raw reply [flat|nested] 3+ messages in thread
* [Discussion] About over-MTU-sized skb in virtualized env
@ 2014-12-03 6:39 Du Fan
2014-12-03 10:50 ` Florian Westphal
0 siblings, 1 reply; 3+ messages in thread
From: Du Fan @ 2014-12-03 6:39 UTC (permalink / raw
To: Florian Westphal
Cc: Thomas Graf, Michael S. Tsirkin, Jesse Gross, Flavio Leitner,
davem@davemloft.net, pshelar, netdev, dev@openvswitch.org,
Du, Fan
Sorry for resend this mail, because my company email is rejected by netdev.
Hi Florian
214 static int ip_finish_output_gso(struct sk_buff *skb)
215 {
216 netdev_features_t features;
217 struct sk_buff *segs;
218 int ret = 0;
219
220 /* common case: locally created skb or seglen is <= mtu */
221 if (((IPCB(skb)->flags & IPSKB_FORWARDED) == 0) ||
222 skb_gso_network_seglen(skb) <= ip_skb_dst_mtu(skb))
223 return ip_finish_output2(skb);
Could you please state _concrete_ reason why locally created skb
length is ＿always＿ fitting into MTU size? or why we needs this
checking.
Especially in below scenario:
http://docs.openstack.org/admin-guide-cloud/content/figures/14/a/a/common/figures/under-the-hood-scenario-1-ovs-compute.png
As many people have discuss it in this thread:
http://marc.info/?t=141715669700004&r=1&w=2
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [Discussion] About over-MTU-sized skb in virtualized env
2014-12-03 6:39 [Discussion] About over-MTU-sized skb in virtualized env Du Fan
@ 2014-12-03 10:50 ` Florian Westphal
0 siblings, 0 replies; 3+ messages in thread
From: Florian Westphal @ 2014-12-03 10:50 UTC (permalink / raw
To: Du Fan
Cc: Florian Westphal, Thomas Graf, Michael S. Tsirkin, Jesse Gross,
Flavio Leitner, davem@davemloft.net, pshelar, netdev,
dev@openvswitch.org, Du, Fan
Du Fan <fengyuleidian0615@gmail.com> wrote:
> Sorry for resend this mail, because my company email is rejected by netdev.
>
>
> Hi Florian
>
> 214 static int ip_finish_output_gso(struct sk_buff *skb)
> 215 {
> 216 netdev_features_t features;
> 217 struct sk_buff *segs;
> 218 int ret = 0;
> 219
> 220 /* common case: locally created skb or seglen is <= mtu */
> 221 if (((IPCB(skb)->flags & IPSKB_FORWARDED) == 0) ||
> 222 skb_gso_network_seglen(skb) <= ip_skb_dst_mtu(skb))
> 223 return ip_finish_output2(skb);
>
> Could you please state _concrete_ reason why locally created skb
> length is ＿always＿ fitting into MTU size? or why we needs this
> checking.
We don't "need" this checking. Its just to avoid skb_gso_network_seglen()
computation for the common (local-out) case.
Locally generated GSO packet is not supposed to exceed dst_mtu, as that
is the PMTU discovery start point in absence of lower/learned value.
^ permalink raw reply [flat|nested] 3+ messages in thread
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2014-12-03 6:39 [Discussion] About over-MTU-sized skb in virtualized env Du Fan
2014-12-03 10:50 ` Florian Westphal
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2014-12-03 5:40 Du, Fan
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