linux-stable.git/net/ipv4/tcp_input.c, branch linux-3.13.y

tcp: properly handle stretch acks in slow start

2013-11-05T00:57:59+00:00

Slow start now increases cwnd by 1 if an ACK acknowledges some packets,
regardless the number of packets. Consequently slow start performance
is highly dependent on the degree of the stretch ACKs caused by
receiver or network ACK compression mechanisms (e.g., delayed-ACK,
GRO, etc).  But slow start algorithm is to send twice the amount of
packets of packets left so it should process a stretch ACK of degree
N as if N ACKs of degree 1, then exits when cwnd exceeds ssthresh. A
follow up patch will use the remainder of the N (if greater than 1)
to adjust cwnd in the congestion avoidance phase.

In addition this patch retires the experimental limited slow start
(LSS) feature. LSS has multiple drawbacks but questionable benefit. The
fractional cwnd increase in LSS requires a loop in slow start even
though it's rarely used. Configuring such an increase step via a global
sysctl on different BDPS seems hard. Finally and most importantly the
slow start overshoot concern is now better covered by the Hybrid slow
start (hystart) enabled by default.

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

Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net

2013-11-04T18:48:30+00:00

Conflicts:
	drivers/net/ethernet/emulex/benet/be.h
	drivers/net/netconsole.c
	net/bridge/br_private.h

Three mostly trivial conflicts.

The net/bridge/br_private.h conflict was a function signature (argument
addition) change overlapping with the extern removals from Joe Perches.

In drivers/net/netconsole.c we had one change adjusting a printk message
whilst another changed "printk(KERN_INFO" into "pr_info(".

Lastly, the emulex change was a new inline function addition overlapping
with Joe Perches's extern removals.

Signed-off-by: David S. Miller

tcp: do not rearm RTO when future data are sacked

2013-10-27T20:50:06+00:00

Patch ed08495c3 "tcp: use RTT from SACK for RTO" always re-arms RTO upon
obtaining a RTT sample from newly sacked data.

But technically RTO should only be re-armed when the data sent before
the last (re)transmission of write queue head are (s)acked. Otherwise
the RTO may continue to extend during loss recovery on data sent
in the future.

Note that RTTs from ACK or timestamps do not have this problem, as the RTT
source must be from data sent before.

The new RTO re-arm policy is
1) Always re-arm RTO if SND.UNA is advanced
2) Re-arm RTO if sack RTT is available, provided the sacked data was
   sent before the last time write_queue_head was sent.

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

tcp: only take RTT from timestamps if new data is acked

2013-10-27T20:50:06+00:00

Patch ed08495c3 "tcp: use RTT from SACK for RTO" has a bug that
it does not check if the ACK acknowledge new data before taking
the RTT sample from TCP timestamps. This patch adds the check
back as required by the RFC.

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

tcp: fix SYNACK RTT estimation in Fast Open

2013-10-27T20:50:06+00:00

tp->lsndtime may not always be the SYNACK timestamp if a passive
Fast Open socket sends data before handshake completes. And if the
remote acknowledges both the data and the SYNACK, the RTT sample
is already taken in tcp_ack(), so no need to call
tcp_update_ack_rtt() in tcp_synack_rtt_meas() aagain.

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

Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net

2013-10-23T20:49:34+00:00

Conflicts:
	drivers/net/usb/qmi_wwan.c
	include/net/dst.h

Trivial merge conflicts, both were overlapping changes.

Signed-off-by: David S. Miller

tcp: initialize passive-side sk_pacing_rate after 3WHS

2013-10-21T22:56:23+00:00

For passive TCP connections, upon receiving the ACK that completes the
3WHS, make sure we set our pacing rate after we get our first RTT
sample.

On passive TCP connections, when we receive the ACK completing the
3WHS we do not take an RTT sample in tcp_ack(), but rather in
tcp_synack_rtt_meas(). So upon receiving the ACK that completes the
3WHS, tcp_ack() leaves sk_pacing_rate at its initial value.

Originally the initial sk_pacing_rate value was 0, so passive-side
connections defaulted to sysctl_tcp_min_tso_segs (2 segs) in skbuffs
made in the first RTT. With a default initial cwnd of 10 packets, this
happened to be correct for RTTs 5ms or bigger, so it was hard to
see problems in WAN or emulated WAN testing.

Since 7eec4174ff ("pkt_sched: fq: fix non TCP flows pacing"), the
initial sk_pacing_rate is 0xffffffff. So after that change, passive
TCP connections were keeping this value (and using large numbers of
segments per skbuff) until receiving an ACK for data.

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

tcp: fix incorrect ca_state in tail loss probe

2013-10-17T19:41:02+00:00

On receiving an ACK that covers the loss probe sequence, TLP
immediately sets the congestion state to Open, even though some packets
are not recovered and retransmisssion are on the way.  The later ACks
may trigger a WARN_ON check in step D of tcp_fastretrans_alert(), e.g.,
https://bugzilla.redhat.com/show_bug.cgi?id=989251

The fix is to follow the similar procedure in recovery by calling
tcp_try_keep_open(). The sender switches to Open state if no packets
are retransmissted. Otherwise it goes to Disorder and let subsequent
ACKs move the state to Recovery or Open.

Reported-By: Michael Sterrett 
Tested-By: Dormando 
Signed-off-by: Yuchung Cheng 
Acked-by: Neal Cardwell 
Signed-off-by: David S. Miller

tcp: use ACCESS_ONCE() in tcp_update_pacing_rate()

2013-10-10T04:08:07+00:00

sk_pacing_rate is read by sch_fq packet scheduler at any time,
with no synchronization, so make sure we update it in a
sensible way. ACCESS_ONCE() is how we instruct compiler
to not do stupid things, like using the memory location
as a temporary variable.

Signed-off-by: Eric Dumazet 
Signed-off-by: David S. Miller

Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net

2013-10-09T03:07:53+00:00

Conflicts:
	include/linux/netdevice.h
	net/core/sock.c

Trivial merge issues.

Removal of "extern" for functions declaration in netdevice.h
at the same time "const" was added to an argument.

Two parallel line additions in net/core/sock.c

Signed-off-by: David S. Miller