On Fri, 2015-06-05 at 16:02 -0700, Martin KaFai Lau wrote:
> On Fri, Jun 05, 2015 at 02:23:55PM -0700, Eric Dumazet wrote:
> > On Fri, 2015-06-05 at 11:02 -0700, Martin KaFai Lau wrote:
> >
> > > tcp_trim_head() does not take the mss_now.
> > > Is it fine to have mss_now <= tcp_skb_mss(skb)? or we can depend on
> > > the tcp_init_tso_segs() in the tcp_write_xmit() to take care of it?
> >
> > It should be fine : packets not yet sent have tcp_skb_pcount()==0,
> > so that tcp_init_tso_segs() can do the computation at the right time.
> hmm.... From tcp_write_xmit(), tcp_init_tso_segs() makes tcp_skb_pcount(skb)
> > 0
> but it may not be sent out immediately (like failing tcp_cwnd_test()). Later,
> this skb is considered for tcp_mtu_probe(), sliced and forgot to update the
> pcount, I think.
Then clear pcount at this point, if this is a requirement.
Or else the test on !tso_segs seems quite lazy to me.
>
> I am probably missing something. Hence, I have a side question
> in tcp_init_tso_segs(), should pcount be also recalculated if
> (tso_segs == 1 && mss_now < skb->len)? Like this:
>
> diff --git i/net/ipv4/tcp_output.c w/net/ipv4/tcp_output.c
> index a369e8a..15d1c44 100644
> --- i/net/ipv4/tcp_output.c
> +++ w/net/ipv4/tcp_output.c
> @@ -1624,7 +1624,8 @@ static int tcp_init_tso_segs(const struct sock *sk,
> struct sk_buff *skb,
> {
> int tso_segs = tcp_skb_pcount(skb);
>
> - if (!tso_segs || (tso_segs > 1 && tcp_skb_mss(skb) != mss_now)) {
> + if (!tso_segs || (tso_segs > 1 && tcp_skb_mss(skb) != mss_now) ||
> + (tso_segs == 1 && mss_now < skb->len)) {
> tcp_set_skb_tso_segs(sk, skb, mss_now);
> tso_segs = tcp_skb_pcount(skb);
> }
See above. Lets keep fast path as fast as possible ;)
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