On Tue, Jul 17, 2018 at 2:16 AM Paolo Abeni <pab...@redhat.com> wrote:
>
> Hi,
>
> On Mon, 2018-07-16 at 16:39 -0700, Cong Wang wrote:
> > On Fri, Jul 13, 2018 at 2:55 AM Paolo Abeni <pab...@redhat.com> wrote:
> > >
> > > When mirred is invoked from the ingress path, and it wants to redirect
> > > the processed packet, it can now use the ACT_REDIRECT action,
> > > filling the tcf_result accordingly.
> > >
> > > This avoids a skb_clone() in the TC S/W data path giving a ~10%
> > > improvement in forwarding performances. Overall TC S/W performances
> > > are now comparable to the kernel openswitch datapath.
>
> Thank you for the feedback.
>
> > Avoiding skb_clone() for redirection is cool, but why need to use
> > skb_do_redirect() here?
>
> Well, it's not needed. I tried to reduce code duplication, and I tried
> to avoid adding another TC_ACT_* value.
If you consider dev_forward_skb(), it is not a duplication.
>
> > There is a subtle difference here:
> >
> > skb_do_redirect() calls __bpf_rx_skb() which calls
> > dev_forward_skb().
> >
> > while the current mirred action doesn't scrub packets when
> > redirecting to ingress (from egress). Although I forget if it is
> > intentionally.
>
> Understood.
>
> A possible option out of this issues would be adding another action
> value - TC_ACT_MIRRED ? - and handle it in sch_handle_egress()[1] with
> the appropriate semantic. That should address also Daniel and Eyal
> concerns.
>
> Would you consider the above acceptable?
If you goal is to get rid of skb_clone(), why not just do the following?
if (tcf_mirred_is_act_redirect(m_eaction)) {
skb2 = skb;
} else {
skb2 = skb_clone(skb, GFP_ATOMIC);
if (!skb2)
goto out;
}
For redirect, we return TC_ACT_SHOT, so upper layer should not
touch the skb after that.
What am I missing here?
