netdev - Re: [PATCH net-next v2] net: core: set and refine qdisc pkt len before tc

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Message-ID: <20150513213348.GC6179@breakpoint.cc>
Date:	Wed, 13 May 2015 23:33:48 +0200
From:	Florian Westphal <fw@...len.de>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Daniel Borkmann <daniel@...earbox.net>, davem@...emloft.net,
	fw@...len.de, ast@...mgrid.com, jhs@...atatu.com,
	netdev@...r.kernel.org
Subject: Re: [PATCH net-next v2] net: core: set and refine qdisc pkt len
 before tc_classify

Eric Dumazet <eric.dumazet@...il.com> wrote:
> > Commit d2788d34885d4ce5ba ("net: sched: further simplify handle_ing")
> > removed the call to qdisc_enqueue_root(). However, after this removal
> > we no longer set qdisc pkt length, which this patch fixes. We make use
> > of qdisc_pkt_len_init() from 1def9238d4aa ("net_sched: more precise
> > pkt_len computation"), which was suggested as the current approach so
> > far does not take into account when GRO builds up GSO packets.
> > 
> > Fixes: d2788d34885d ("net: sched: further simplify handle_ing")
> > Suggested-by: Jamal Hadi Salim <jhs@...atatu.com>
> > Signed-off-by: Florian Westphal <fw@...len.de>
> > Signed-off-by: Daniel Borkmann <daniel@...earbox.net>
> > ---
> >  v1->v2:
> >   - use qdisc_pkt_len_init() as suggested, thanks!
> >
> > @@ -3541,9 +3541,11 @@ static inline struct sk_buff *handle_ing(struct sk_buff *skb,
> >  		*pt_prev = NULL;
> >  	}
> >  
> > -	qdisc_bstats_update_cpu(cl->q, skb);
> > +	qdisc_pkt_len_init(skb);
[..]
> 
> Is qdisc_pkt_len_init() still inlined, now it has 2 callers ?

gcc 4.8.4, OPTIMIZE_FOR_SIZE=n: nope, callq.

> People using policers on ingress are very often disabling GRO for
> various historical reasons.

right, ingress policing is rather poor with GRO (or you need to set mtu 64000
on the tc police cmd line).

> Since handle_ing() is very uncommon, I would prefer not slowing down tx
> just so that GRO ~5% error in ingress is fixed.

Hmm, so whats you suggestion?  Just use

qdisc_skb_cb(skb)->pkt_len = skb->len;

like in v1 of the patch set?
resurrect qdisc_enqueue_root?
set always_inline (i'd prefer not, its not very small)?

Any other idea?

Thanks!
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