linux-toradex.git/Documentation/networking, branch v3.10.26

tcp: tsq: restore minimal amount of queueing

2013-12-08T15:29:24+00:00

[ Upstream commit 98e09386c0ef4dfd48af7ba60ff908f0d525cdee ]

After commit c9eeec26e32e ("tcp: TSQ can use a dynamic limit"), several
users reported throughput regressions, notably on mvneta and wifi
adapters.

802.11 AMPDU requires a fair amount of queueing to be effective.

This patch partially reverts the change done in tcp_write_xmit()
so that the minimal amount is sysctl_tcp_limit_output_bytes.

It also remove the use of this sysctl while building skb stored
in write queue, as TSO autosizing does the right thing anyway.

Users with well behaving NICS and correct qdisc (like sch_fq),
can then lower the default sysctl_tcp_limit_output_bytes value from
128KB to 8KB.

This new usage of sysctl_tcp_limit_output_bytes permits each driver
authors to check how their driver performs when/if the value is set
to a minimum of 4KB.

Normally, line rate for a single TCP flow should be possible,
but some drivers rely on timers to perform TX completion and
too long TX completion delays prevent reaching full throughput.

Fixes: c9eeec26e32e ("tcp: TSQ can use a dynamic limit")
Signed-off-by: Eric Dumazet 
Reported-by: Sujith Manoharan 
Reported-by: Arnaud Ebalard 
Tested-by: Sujith Manoharan 
Cc: Felix Fietkau 
Signed-off-by: David S. Miller 
Signed-off-by: Greg Kroah-Hartman

tcp: TSO packets automatic sizing

2013-11-04T12:30:59+00:00

[ Upstream commits 6d36824e730f247b602c90e8715a792003e3c5a7,
  02cf4ebd82ff0ac7254b88e466820a290ed8289a, and parts of
  7eec4174ff29cd42f2acfae8112f51c228545d40 ]

After hearing many people over past years complaining against TSO being
bursty or even buggy, we are proud to present automatic sizing of TSO
packets.

One part of the problem is that tcp_tso_should_defer() uses an heuristic
relying on upcoming ACKS instead of a timer, but more generally, having
big TSO packets makes little sense for low rates, as it tends to create
micro bursts on the network, and general consensus is to reduce the
buffering amount.

This patch introduces a per socket sk_pacing_rate, that approximates
the current sending rate, and allows us to size the TSO packets so
that we try to send one packet every ms.

This field could be set by other transports.

Patch has no impact for high speed flows, where having large TSO packets
makes sense to reach line rate.

For other flows, this helps better packet scheduling and ACK clocking.

This patch increases performance of TCP flows in lossy environments.

A new sysctl (tcp_min_tso_segs) is added, to specify the
minimal size of a TSO packet (default being 2).

A follow-up patch will provide a new packet scheduler (FQ), using
sk_pacing_rate as an input to perform optional per flow pacing.

This explains why we chose to set sk_pacing_rate to twice the current
rate, allowing 'slow start' ramp up.

sk_pacing_rate = 2 * cwnd * mss / srtt

v2: Neal Cardwell reported a suspect deferring of last two segments on
initial write of 10 MSS, I had to change tcp_tso_should_defer() to take
into account tp->xmit_size_goal_segs

Signed-off-by: Eric Dumazet 
Cc: Neal Cardwell 
Cc: Yuchung Cheng 
Cc: Van Jacobson 
Cc: Tom Herbert 
Acked-by: Yuchung Cheng 
Acked-by: Neal Cardwell 
Signed-off-by: David S. Miller 
Signed-off-by: Greg Kroah-Hartman

tcp: doc : fix the syncookies default value

2013-06-24T07:26:26+00:00

syncookies is on for default since in commit e994b7c901
(tcp: Don't make syn cookies initial setting depend on CONFIG_SYSCTL).

And fix a typo of CONFIG_SYN_COOKIES.

Signed-off-by: Shan Wei 
Signed-off-by: David S. Miller

packet: doc: update timestamping part

2013-04-25T05:22:22+00:00

Bring the timestamping section in sync with the implementation.

Signed-off-by: Daniel Borkmann 
Acked-by: Willem de Bruijn 
Signed-off-by: David S. Miller

netlink: add documentation for memory mapped I/O

2013-04-19T18:58:36+00:00

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

stmmac: review driver documentation

2013-04-08T20:55:27+00:00

This patch reviews the driver documentation file;
for example, there were some new fields (in the driver
module parameter section) and the ptp files were
not documented.

Signed-off-by: Giuseppe Cavallaro 
Signed-off-by: David S. Miller

ieee802154/nl-mac.c: make some MLME operations optional

2013-04-08T16:00:16+00:00

Check for NULL before calling the following operations from "struct
ieee802154_mlme_ops": assoc_req, assoc_resp, disassoc_req, start_req,
and scan_req.

This fixes a current oops where those functions are called but not
implemented. It also updates the documentation to clarify that they
are now optional by design. If a call to an unimplemented function
is attempted, the kernel returns EOPNOTSUPP via netlink.

The following operations are still required: get_phy, get_pan_id,
get_short_addr, and get_dsn.

Note that the places where this patch changes the initialization
of "ret" should not affect the rest of the code since "ret" was
always set (again) before returning its value.

Signed-off-by: Werner Almesberger 
Signed-off-by: David S. Miller

doc: packet: add minimal TPACKET_V3 example code

2013-03-30T21:40:27+00:00

Lost in space for a long time, but it finally came back to us from
some ancient code tombs. This patch adds a minimal runnable example
of Linux' packet mmap(2) from Chetan Loke's TPACKET_V3. Special
thanks to David S. Miller, and also Eric Leblond and Victor Julien!

Cc: Eric Leblond 
Cc: Victor Julien 
Signed-off-by: Daniel Borkmann 
Signed-off-by: David S. Miller

stmmac: update the Doc and Version (PTP+SGMII)

2013-03-26T16:53:37+00:00

This patch updates the stmmac.txt file adding information related to the PTP
and SGMII/RGMII supports.

Also the patch updates the driver version to: March_2013.

Signed-off-by: Giuseppe Cavallaro 
Signed-off-by: David S. Miller

tcp: implement RFC5682 F-RTO

2013-03-21T15:47:51+00:00

This patch implements F-RTO (foward RTO recovery):

When the first retransmission after timeout is acknowledged, F-RTO
sends new data instead of old data. If the next ACK acknowledges
some never-retransmitted data, then the timeout was spurious and the
congestion state is reverted.  Otherwise if the next ACK selectively
acknowledges the new data, then the timeout was genuine and the
loss recovery continues. This idea applies to recurring timeouts
as well. While F-RTO sends different data during timeout recovery,
it does not (and should not) change the congestion control.

The implementaion follows the three steps of SACK enhanced algorithm
(section 3) in RFC5682. Step 1 is in tcp_enter_loss(). Step 2 and
3 are in tcp_process_loss().  The basic version is not supported
because SACK enhanced version also works for non-SACK connections.

The new implementation is functionally in parity with the old F-RTO
implementation except the one case where it increases undo events:
In addition to the RFC algorithm, a spurious timeout may be detected
without sending data in step 2, as long as the SACK confirms not
all the original data are dropped. When this happens, the sender
will undo the cwnd and perhaps enter fast recovery instead. This
additional check increases the F-RTO undo events by 5x compared
to the prior implementation on Google Web servers, since the sender
often does not have new data to send for HTTP.

Note F-RTO may detect spurious timeout before Eifel with timestamps
does so.

Signed-off-by: Yuchung Cheng 
Acked-by: Eric Dumazet 
Acked-by: Neal Cardwell 
Signed-off-by: David S. Miller