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SubjectRe: [PATCH][TCP]: simplify tcp_mark_lost_retrans()
On Wed, 7 Jan 2009, Ilpo Järvinen wrote:

> On Wed, 7 Jan 2009, Arnd Hannemann wrote:
>
> > I noticed
>
> Good that somebody else is looking TCP code besides me... :-)
>
> > that in tcp_mark_lost_retrans the for-loop is only entered
> > if tcp_is_fack(tp) evaluates to true:
> >
> > if (!tcp_is_fack(tp) || !tp->retrans_out ||
> > !after(received_upto, tp->lost_retrans_low) ||
> > icsk->icsk_ca_state != TCP_CA_Recovery)
> > return;
> >
> > Therefore the following check in the for-loop seems to be redundant,
> > because it always evaluates to true:
> >
> > (tcp_is_fack(tp) ||
> > !before(received_upto,
> > ack_seq + tp->reordering * tp->mss_cache))
> >
> > Did I miss something?
>
> It was just a left over from the RFC3517 SACK addition which added that
> !tcp_is_fack(tp) there above. ...It would have been nice to have similar
> lost rexmit feature without FACK as well but calculating that wasn't
> trivial (or I didn't find that too trivial) and could end up being
> extremely expensive in case of large holes. (So I also left it there as
> sort of reminder).
>
> On the second thought, it would be possible to count skbs we pass while
> walking from the beginning and use that a remaining_sacked counter
> to get rid of all heurestics too and base the counting only on sacked
> stuff which aligns with the spirit of rfc3517 much better than
> sacked+holes used by fack.

Nah, tried to do that that wasn't working nicely either... Since there is
a need to know how many sack blocks reside between ack_seq and
received_upto, not the number of sack blocks between skb and
received_upto...

--
i.
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