-----Original Message-----
> From: Paolo Abeni <pabeni@xxxxxxxxxx>
> Sent: Tuesday, May 20, 2025 12:04 PM
> To: Chia-Yu Chang (Nokia) <chia-yu.chang@xxxxxxxxxxxxxxxxxxx>; linux-doc@xxxxxxxxxxxxxxx; corbet@xxxxxxx; horms@xxxxxxxxxx; dsahern@xxxxxxxxxx; kuniyu@xxxxxxxxxx; bpf@xxxxxxxxxxxxxxx; netdev@xxxxxxxxxxxxxxx; dave.taht@xxxxxxxxx; jhs@xxxxxxxxxxxx; kuba@xxxxxxxxxx; stephen@xxxxxxxxxxxxxxxxxx; xiyou.wangcong@xxxxxxxxx; jiri@xxxxxxxxxxx; davem@xxxxxxxxxxxxx; edumazet@xxxxxxxxxx; andrew+netdev@xxxxxxx; donald.hunter@xxxxxxxxx; ast@xxxxxxxxxxx; liuhangbin@xxxxxxxxx; shuah@xxxxxxxxxx; linux-kselftest@xxxxxxxxxxxxxxx; ij@xxxxxxxxxx; ncardwell@xxxxxxxxxx; Koen De Schepper (Nokia) <koen.de_schepper@xxxxxxxxxxxxxxxxxxx>; g.white <g.white@xxxxxxxxxxxxx>; ingemar.s.johansson@xxxxxxxxxxxx; mirja.kuehlewind@xxxxxxxxxxxx; cheshire@xxxxxxxxx; rs.ietf@xxxxxx; Jason_Livingood@xxxxxxxxxxx; vidhi_goel <vidhi_goel@xxxxxxxxx>
> Subject: Re: [PATCH v7 net-next 14/15] tcp: accecn: try to fit AccECN option with SACK
>
>
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> On 5/14/25 3:56 PM, chia-yu.chang@xxxxxxxxxxxxxxxxxxx wrote:
> > From: Ilpo Järvinen <ij@xxxxxxxxxx>
> >
> > As SACK blocks tend to eat all option space when there are many holes,
> > it is useful to compromise on sending many SACK blocks in every ACK
> > and try to fit AccECN option there by reduction the number of SACK
> > blocks. But never go below two SACK blocks because of AccECN option.
> >
> > As AccECN option is often not put to every ACK, the space hijack is
> > usually only temporary.
> >
> > Signed-off-by: Ilpo Järvinen <ij@xxxxxxxxxx>
> > Signed-off-by: Chia-Yu Chang <chia-yu.chang@xxxxxxxxxxxxxxxxxxx>
> > ---
> > net/ipv4/tcp_output.c | 15 ++++++++++++++-
> > 1 file changed, 14 insertions(+), 1 deletion(-)
> >
> > diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c index
> > b630923c4cef..d9d3cc8dbb5b 100644
> > --- a/net/ipv4/tcp_output.c
> > +++ b/net/ipv4/tcp_output.c
> > @@ -982,8 +982,21 @@ static int tcp_options_fit_accecn(struct tcp_out_options *opts, int required,
> > opts->num_accecn_fields--;
> > size -= TCPOLEN_ACCECN_PERFIELD;
> > }
> > - if (opts->num_accecn_fields < required)
> > + if (opts->num_accecn_fields < required) {
> > + if (opts->num_sack_blocks > 2) {
> > + /* Try to fit the option by removing one SACK block */
> > + opts->num_sack_blocks--;
> > + size = tcp_options_fit_accecn(opts, required,
> > + remaining +
> > + TCPOLEN_SACK_PERBLOCK,
> > +
> > + max_combine_saving);
>
> How deep is the recursion level, worst case? In any case please try to avoid recursion entirely. Possibly a 'goto' statement would help.
>
> /P
Hi Paolo,
Thanks for the feedback, in this case up to 2 extra levels will be needed.
And the recursion will be avoided in the next version.
BRs,
Chia-Yu
