linux-toradex.git/include/linux/tcp.h, branch v2.6.26-rc5

tcp: Make prior_ssthresh a u32

2008-05-22T00:40:05+00:00

If previous window was above representable values of u16,
strange things will happen if undo with the truncated value
is called for. Alternatively, this could be fixed by some
max trickery but that would limit undoing high-speed undos.

Adds 16-bit hole but there isn't anything to fill it with.

Signed-off-by: Ilpo Järvinen 
Signed-off-by: David S. Miller

[TCP]: TCP_DEFER_ACCEPT updates - process as established

2008-03-21T23:33:01+00:00

Change TCP_DEFER_ACCEPT implementation so that it transitions a
connection to ESTABLISHED after handshake is complete instead of
leaving it in SYN-RECV until some data arrvies. Place connection in
accept queue when first data packet arrives from slow path.

Benefits:
  - established connection is now reset if it never makes it
   to the accept queue

 - diagnostic state of established matches with the packet traces
   showing completed handshake

 - TCP_DEFER_ACCEPT timeouts are expressed in seconds and can now be
   enforced with reasonable accuracy instead of rounding up to next
   exponential back-off of syn-ack retry.

Signed-off-by: Patrick McManus 
Signed-off-by: David S. Miller

[TCP]: Rewrite SACK block processing & sack_recv_cache use

2008-01-28T22:54:07+00:00

Key points of this patch are:

  - In case new SACK information is advance only type, no skb
    processing below previously discovered highest point is done
  - Optimize cases below highest point too since there's no need
    to always go up to highest point (which is very likely still
    present in that SACK), this is not entirely true though
    because I'm dropping the fastpath_skb_hint which could
    previously optimize those cases even better. Whether that's
    significant, I'm not too sure.

Currently it will provide skipping by walking. Combined with
RB-tree, all skipping would become fast too regardless of window
size (can be done incrementally later).

Previously a number of cases in TCP SACK processing fails to
take advantage of costly stored information in sack_recv_cache,
most importantly, expected events such as cumulative ACK and new
hole ACKs. Processing on such ACKs result in rather long walks
building up latencies (which easily gets nasty when window is
huge). Those latencies are often completely unnecessary
compared with the amount of _new_ information received, usually
for cumulative ACK there's no new information at all, yet TCP
walks whole queue unnecessary potentially taking a number of
costly cache misses on the way, etc.!

Since the inclusion of highest_sack, there's a lot information
that is very likely redundant (SACK fastpath hint stuff,
fackets_out, highest_sack), though there's no ultimate guarantee
that they'll remain the same whole the time (in all unearthly
scenarios). Take advantage of this knowledge here and drop
fastpath hint and use direct access to highest SACKed skb as
a replacement.

Effectively "special cased" fastpath is dropped. This change
adds some complexity to introduce better coveraged "fastpath",
though the added complexity should make TCP behave more cache
friendly.

The current ACK's SACK blocks are compared against each cached
block individially and only ranges that are new are then scanned
by the high constant walk. For other parts of write queue, even
when in previously known part of the SACK blocks, a faster skip
function is used (if necessary at all). In addition, whenever
possible, TCP fast-forwards to highest_sack skb that was made
available by an earlier patch. In typical case, no other things
but this fast-forward and mandatory markings after that occur
making the access pattern quite similar to the former fastpath
"special case".

DSACKs are special case that must always be walked.

The local to recv_sack_cache copying could be more intelligent
w.r.t DSACKs which are likely to be there only once but that
is left to a separate patch.

Signed-off-by: Ilpo Järvinen 
Signed-off-by: David S. Miller

[TCP]: Earlier SACK block verification & simplify access to them

2008-01-28T22:54:07+00:00

Signed-off-by: Ilpo Järvinen 
Signed-off-by: David S. Miller

[TCP]: Convert highest_sack to sk_buff to allow direct access

2008-01-28T22:54:03+00:00

It is going to replace the sack fastpath hint quite soon... :-)

Signed-off-by: Ilpo Järvinen 
Signed-off-by: David S. Miller

[TCP]: Make snd_cwnd_cnt 32-bit

2007-10-15T19:59:43+00:00

Very little point of having 32-bit snd_cnwd if this is not
32-bit as well, as a number of snd_cwnd incrementation formulas
assume that snd_cwnd_cnt can be at least as large as snd_cwnd.

Whether 32-bit is useful was discussed when e0ef57cc56c3c96
was made:
  http://marc.info/?l=linux-netdev&m=117218144409825&w=2

Signed-off-by: Ilpo Järvinen 
Signed-off-by: David S. Miller

[TCP]: Limit processing lost_retrans loop to work-to-do cases

2007-10-12T00:36:13+00:00

This addition of lost_retrans_low to tcp_sock might be
unnecessary, it's not clear how often lost_retrans worker is
executed when there wasn't work to do.

Signed-off-by: Ilpo Järvinen 
Signed-off-by: David S. Miller

[TCP]: Comment fastpath_cnt_hint off-by-one trap

2007-10-10T23:54:47+00:00

Signed-off-by: Ilpo Järvinen 
Signed-off-by: David S. Miller

[TCP]: Update comment about highest_sack validity

2007-10-10T23:48:00+00:00

This stale info came from the original idea, which proved to be
unnecessarily complex, sacked_out > 0 is easy to do and that when
it's going to be needed anyway (it _can_ be valid also when
sacked_out == 0 but there's not going to be a guarantee about it
for now).

Signed-off-by: Ilpo Järvinen 
Signed-off-by: David S. Miller

[TCP]: Tighten tcp_sock's belt, drop left_out

2007-10-10T23:47:55+00:00

It is easily calculable when needed and user are not that many
after all.

Signed-off-by: Ilpo Järvinen 
Signed-off-by: David S. Miller