From mboxrd@z Thu Jan  1 00:00:00 1970
From: Eric Dumazet <eric.dumazet@gmail.com>
Subject: Re: [PATCH v2 net-next] tcp: allow drivers to tweak TSQ logic
Date: Tue, 28 Nov 2017 09:33:49 -0800
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Cc: netdev <netdev@vger.kernel.org>,
        Johannes Berg <johannes.berg@intel.com>,
        Toke =?ISO-8859-1?Q?H=F8iland-J=F8rgensen?= <toke@toke.dk>,
        Kir Kolyshkin <kir@openvz.org>
To: Felix Fietkau <nbd@nbd.name>, David Miller <davem@davemloft.net>
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On Tue, 2017-11-28 at 14:10 +0100, Felix Fietkau wrote:
> On 2017-11-12 00:54, Eric Dumazet wrote:
> > From: Eric Dumazet <edumazet@google.com>
> > 
> > I had many reports that TSQ logic breaks wifi aggregation.
> > 
> > Current logic is to allow up to 1 ms of bytes to be queued into
> > qdisc
> > and drivers queues.
> > 
> > But Wifi aggregation needs a bigger budget to allow bigger rates to
> > be discovered by various TCP Congestion Controls algorithms.
> > 
> > This patch adds an extra socket field, allowing wifi drivers to
> > select
> > another log scale to derive TCP Small Queue credit from current
> > pacing
> > rate.
> > 
> > Initial value is 10, meaning that this patch does not change
> > current
> > behavior.
> > 
> > We expect wifi drivers to set this field to smaller values (tests
> > have
> > been done with values from 6 to 9)
> > 
> > They would have to use following template :
> > 
> > if (skb->sk && skb->sk->sk_pacing_shift != MY_PACING_SHIFT)
> >      skb->sk->sk_pacing_shift = MY_PACING_SHIFT;
> 
> I did some experiments with this approach (with your patch backported
> to
> a 4.9 kernel), and I got some crashes.
> After looking at the crashes and code some more, it seems that this
> would need some extra checks to ensure that skb->sk is a full struct
> sock, instead of just a struct request_sock.
> Should this be done by checking for skb->sk->sk_state ==
> TCP_ESTABLISHED? It seems to me that this might introduce some extra
> overhead.
> 
Hi Felix.

Answer is in the question, the pseudo code in the changelog was not
100% correct.

I will add following helper to net-next I guess :

void sk_pacing_shift_update(struct sock *sk, int val)
{
	if (!sk || !sk_fullsock(sk) || sk->sk_pacing_shift == val)
		return;
	sk->sk_pacing_shift = val;
}


Then you might use it like that :

	sk_pacing_shift_update(skb->sk, 7);

Thanks.