Re: [PATCH net 1/2] geneve, vxlan: Don't check skb_dst() twice
Le 15/10/2018 à 13:08, Stefano Brivio a écrit :
> On Mon, 15 Oct 2018 12:19:41 +0200
> Nicolas Dichtel wrote:
>
>> Le 12/10/2018 à 23:53, Stefano Brivio a écrit :
>>> Commit f15ca723c1eb ("net: don't call update_pmtu unconditionally") avoids
>>> that we try updating PMTU for a non-existent destination, but didn't clean
>>> up cases where the check was already explicit. Drop those redundant checks.
>>>
>> Yes, I leave them to avoid calculating the new mtu value when not needed. We
>> are
>> in the xmit path.
>
> Before 2/2 of this series, though, we call skb_dst_update_pmtu() (and
> in turn dst->ops->update_pmtu()) for *every* packet with a dst, which
Not if dst is of type md_dst_ops.
> I'd dare saying is by far the most common case. Besides, 2/2 needs
> anyway to calculate the MTU to fix a bug.
>
> So I think this is a vast improvement overall.
Fair point.
Re: [PATCH net 1/2] geneve, vxlan: Don't check skb_dst() twice
On Mon, 15 Oct 2018 12:19:41 +0200
Nicolas Dichtel wrote:
> Le 12/10/2018 à 23:53, Stefano Brivio a écrit :
> > Commit f15ca723c1eb ("net: don't call update_pmtu unconditionally") avoids
> > that we try updating PMTU for a non-existent destination, but didn't clean
> > up cases where the check was already explicit. Drop those redundant checks.
> >
> Yes, I leave them to avoid calculating the new mtu value when not needed. We
> are
> in the xmit path.
Before 2/2 of this series, though, we call skb_dst_update_pmtu() (and
in turn dst->ops->update_pmtu()) for *every* packet with a dst, which
I'd dare saying is by far the most common case. Besides, 2/2 needs
anyway to calculate the MTU to fix a bug.
So I think this is a vast improvement overall.
If we want to improve this further and avoid any indirect calls in the
most common path, we would need to cache the MTU in the dst -- it's
probably doable, but I would fix the specific issue addressed by 2/2
first.
--
Stefano
Re: [PATCH net 1/2] geneve, vxlan: Don't check skb_dst() twice
Le 12/10/2018 à 23:53, Stefano Brivio a écrit :
> Commit f15ca723c1eb ("net: don't call update_pmtu unconditionally") avoids
> that we try updating PMTU for a non-existent destination, but didn't clean
> up cases where the check was already explicit. Drop those redundant checks.
Yes, I leave them to avoid calculating the new mtu value when not needed. We are
in the xmit path.
As skb_dst_update_pmtu() is inlined, we probably don't care, but gcc could still
decide to not inline it.
Regards,
Nicolas
