linux-toradex.git/net/dccp/ccids/ccid3.h, branch v4.4.95

dccp ccid-3: Remove redundant 'options_received' struct

2010-09-21T10:14:26+00:00

The `options_received' struct is redundant, since it re-duplicates the existing
`p' and `x_recv' fields. This patch removes the sub-struct and migrates the
format conversion operations to ccid3_hc_tx_parse_options().

Signed-off-by: Gerrit Renker

dccp ccid-3: remove dead states

2010-09-21T10:14:26+00:00

This patch is thanks to an investigation by Leandro Sales de Melo and his
colleagues. They worked out two state diagrams which highlight the fact that
the xxx_TERM states in CCID-3/4 are in fact not necessary.

And this can be confirmed by in turn looking at the code: the xxx_TERM states
are only ever set in ccid3_hc_{rx,tx}_exit(): when CCID-3 sets the state
to xxx_TERM, it is at a time where no more processing should be going on,
hence it is not necessary to introduce a dedicated exit state - this is already
implied by unloading the CCID.

Signed-off-by: Gerrit Renker

dccp ccid-3: Simplify and consolidate tx_parse_options

2010-09-15T10:36:02+00:00

This simplifies and consolidates the TX option-parsing code:

 1. The Loss Intervals option is not currently used, so dead code related to
    this option is removed. I am aware of no plans to support the option, but
    if someone wants to implement it (e.g. for inter-op tests), it is better
    to start afresh than having to also update currently unused code.

 2. The Loss Event and Receive Rate options have a lot of code in common (both
    are 32 bit, both have same length etc.), so this is consolidated.

 3. The test against GSR is not necessary, because
    - on first loading CCID3, ccid_new() zeroes out all fields in the socket;
    - ccid3_hc_tx_packet_recv() treats 0 and ~0U equivalently, due to

	pinv = opt_recv->ccid3or_loss_event_rate;
	if (pinv == ~0U || pinv == 0)
		hctx->p = 0;

    - as a result, the sequence number field is removed from opt_recv.

Signed-off-by: Gerrit Renker

dccp ccid-3: A lower bound for the inter-packet scheduling algorithm

2010-09-15T10:36:01+00:00

This fixes a subtle bug in the calculation of the inter-packet gap and shows
that t_delta, as it is currently used, is not needed.

The algorithm from RFC 5348, 8.3 below continually computes a send time t_nom,
which is initialised with the current time t_now; t_gran = 1E6 / HZ specifies
the scheduling granularity, s the packet size, and X the sending rate:

  t_distance = t_nom - t_now;		// in microseconds
  t_delta    = min(t_ipi, t_gran) / 2;	// `delta' parameter in microseconds

  if (t_distance >= t_delta) {
	reschedule after (t_distance / 1000) milliseconds;
  } else {
  	t_ipi  = s / X;			// inter-packet interval in usec
	t_nom += t_ipi;			// compute the next send time
	send packet now;
  }

Problem:
--------
Rescheduling requires a conversion into milliseconds (sk_reset_timer()). The
highest jiffy resolution with HZ=1000 is 1 millisecond, so using a higher
granularity does not make much sense here.

As a consequence, values of t_distance < 1000 are truncated to 0. This issue
has so far been resolved by using instead

  if (t_distance >= t_delta + 1000)
	reschedule after (t_distance / 1000) milliseconds;

This is unnecessarily large, a lower bound is t_delta' = max(t_delta, 1000).
And it implies a further simplification:

 a) when HZ >= 500, then t_delta <= t_gran/2 = 10^6/(2*HZ) <= 1000, so that
    t_delta' = MAX(1000, t_delta) = 1000 (constant value);

 b) when HZ < 500, then t_delta = 1/2*MIN(rtt, t_ipi, t_gran) <= t_gran/2,
    so that 1000 <= t_delta' <= t_gran/2.

The maximum error of using a constant t_delta in (b) is less than half a jiffy.

Fix:
----
The patch replaces t_delta with a constant, whose value depends on CONFIG_HZ,
changing the above algorithm to:

  if (t_distance >= t_delta')
	reschedule after (t_distance / 1000) milliseconds;

where t_delta' = 10^6/(2*HZ) if HZ < 500, and t_delta' = 1000 otherwise.

Signed-off-by: Gerrit Renker

dccp ccid-3: use per-route RTO or TCP RTO as fallback

2010-08-30T20:45:28+00:00

This makes RTAX_RTO_MIN also available to CCID-3, replacing the compile-time
RTO lower bound with a per-route tunable value.

The original Kconfig option solved the problem that a very low RTT (in the
order of HZ) can trigger too frequent and unnecessary reductions of the
sending rate.

This tunable does not affect the initial RTO value of 2 seconds specified in
RFC 5348, section 4.2 and Appendix B. But like the hardcoded Kconfig value,
it allows to adapt to network conditions.

The same effect as the original Kconfig option of 100ms is now achieved by

> ip route replace to unicast 192.168.0.0/24 rto_min 100j dev eth0

(assuming HZ=1000).

Signed-off-by: Gerrit Renker 
Signed-off-by: David S. Miller

ccid: ccid-2/3 code cosmetics

2010-08-24T03:13:29+00:00

This patch collects cosmetics-only changes to separate these from
code changes:
 * update with regard to CodingStyle and whitespace changes,
 * documentation:
   - adding/revising comments,
   - remove CCID-3 RX socket documentation which is either
     duplicate or refers to fields that no longer exist,
 * expand embedded tfrc_tx_info struct inline for consistency,
   removing indirections via #define.

Signed-off-by: Gerrit Renker 
Signed-off-by: David S. Miller

dccp ccid-3: Overhaul CCID naming convention 2/2

2009-10-07T20:51:22+00:00

This implements the new naming scheme also for CCID-3.

Signed-off-by: Gerrit Renker 
Acked-by: Arnaldo Carvalho de Melo 
Signed-off-by: David S. Miller

net-next-2.6 [PATCH 1/1] dccp: ccids whitespace-cleanup / CodingStyle

2009-09-15T00:02:54+00:00

No code change, cosmetical changes only:

 * whitespace cleanup via scripts/cleanfile,
 * remove self-references to filename at top of files,
 * fix coding style (extraneous brackets),
 * fix documentation style (kernel-doc-nano-HOWTO).

Thanks are due to Ivo Augusto Calado who raised these issues by
submitting good-quality patches.

Signed-off-by: Gerrit Renker 
Signed-off-by: David S. Miller

[CCID3]: Use a function to update p_inv, and p is never used

2008-01-28T22:58:21+00:00

This patch
 1) concentrates previously scattered computation of p_inv into one function;
 2) removes the `p' element of the CCID3 RX sock (it is redundant);
 3) makes the tfrc_rx_info structure standalone, only used on demand.

Signed-off-by: Gerrit Renker 
Signed-off-by: Ian McDonald 
Signed-off-by: Arnaldo Carvalho de Melo 
Signed-off-by: David S. Miller

[CCID3]: Interface CCID3 code with newer Loss Intervals Database

2008-01-28T22:57:20+00:00

This hooks up the TFRC Loss Interval database with CCID 3 packet reception.
In addition, it makes the CCID-specific computation of the first loss
interval (which requires access to all the guts of CCID3) local to ccid3.c.

The patch also fixes an omission in the DCCP code, that of a default /
fallback RTT value (defined in section 3.4 of RFC 4340 as 0.2 sec); while
at it, the  upper bound of 4 seconds for an RTT sample has  been reduced to
match the initial TCP RTO value of 3 seconds from[RFC 1122, 4.2.3.1].

Signed-off-by: Gerrit Renker 
Signed-off-by: Ian McDonald 
Signed-off-by: Arnaldo Carvalho de Melo 
Signed-off-by: David S. Miller