Upcoming congestion controls for TCP require usec resolution for RTT
estimations. Millisecond resolution is simply not enough these days.
FQ/pacing in DC environments also require this change for finer control
and removal of bimodal behavior due to the current hack in
tcp_update_pacing_rate() for 'small rtt'
TCP_CONG_RTT_STAMP is no longer needed.
As Julian Anastasov pointed out, we need to keep user compatibility :
tcp_metrics used to export RTT and RTTVAR in msec resolution,
so we added RTT_US and RTTVAR_US. An iproute2 patch is needed
to use the new attributes if provided by the kernel.
In this example ss command displays a srtt of 32 usecs (10Gbit link)
lpk51:~# ./ss -i dst lpk52
Netid State Recv-Q Send-Q Local Address:Port Peer
Address:Port
tcp ESTAB 0 1 10.246.11.51:42959
10.246.11.52:64614
cubic wscale:6,6 rto:201 rtt:0.032/0.001 ato:40 mss:1448
cwnd:10 send
3620.0Mbps pacing_rate 7240.0Mbps unacked:1 rcv_rtt:993 rcv_space:29559
Updated iproute2 ip command displays :
lpk51:~# ./ip tcp_metrics | grep 10.246.11.52
10.246.11.52 age 561.914sec cwnd 10 rtt 274us rttvar 213us source
10.246.11.51
Old binary displays :
lpk51:~# ip tcp_metrics | grep 10.246.11.52
10.246.11.52 age 561.914sec cwnd 10 rtt 250us rttvar 125us source
10.246.11.51
With help from Julian Anastasov, Stephen Hemminger and Yuchung Cheng
Signed-off-by: Eric Dumazet <edumazet@google.com>
Acked-by: Neal Cardwell <ncardwell@google.com>
Cc: Stephen Hemminger <stephen@networkplumber.org>
Cc: Yuchung Cheng <ycheng@google.com>
Cc: Larry Brakmo <brakmo@google.com>
Cc: Julian Anastasov <ja@ssi.bg>
Signed-off-by: David S. Miller <davem@davemloft.net>
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 <ycheng@google.com>
Signed-off-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
The patch below updates broken web addresses in the kernel
Signed-off-by: Justin P. Mattock <justinmattock@gmail.com>
Cc: Maciej W. Rozycki <macro@linux-mips.org>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Finn Thain <fthain@telegraphics.com.au>
Cc: Randy Dunlap <rdunlap@xenotime.net>
Cc: Matt Turner <mattst88@gmail.com>
Cc: Dimitry Torokhov <dmitry.torokhov@gmail.com>
Cc: Mike Frysinger <vapier.adi@gmail.com>
Acked-by: Ben Pfaff <blp@cs.stanford.edu>
Acked-by: Hans J. Koch <hjk@linutronix.de>
Reviewed-by: Finn Thain <fthain@telegraphics.com.au>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
On Sun, 2009-11-22 at 16:31 -0800, David Miller wrote:
> It should be of the form:
> if (x &&
> y)
>
> or:
> if (x && y)
>
> Fix patches, rather than complaints, for existing cases where things
> do not follow this pattern are certainly welcome.
Also collapsed some multiple tabs to single space.
Signed-off-by: Joe Perches <joe@perches.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
It seems that implementation in yeah was inconsistent to what
other did as it would increase cwnd one ack earlier than the
others do.
Size benefits:
bictcp_cong_avoid | -36
tcp_cong_avoid_ai | +52
bictcp_cong_avoid | -34
tcp_scalable_cong_avoid | -36
tcp_veno_cong_avoid | -12
tcp_yeah_cong_avoid | -38
= -104 bytes total
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@helsinki.fi>
Signed-off-by: David S. Miller <davem@davemloft.net>
From: Lachlan Andrew <lachlan.andrew@gmail.com>
There is an overflow bug in net/ipv4/tcp_vegas.c for large BDPs
(e.g. 400Mbit/s, 400ms). The multiplication (old_wnd *
vegas->baseRTT) << V_PARAM_SHIFT overflows a u32.
[ Fix tcp_veno.c too, it has similar calculations. -DaveM ]
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@helsinki.fi>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>
This patch changes the API for the callback that is done after an ACK is
received. It solves a couple of issues:
* Some congestion controls want higher resolution value of RTT
(controlled by TCP_CONG_RTT_SAMPLE flag). These don't really want a ktime, but
all compute a RTT in microseconds.
* Other congestion control could use RTT at jiffies resolution.
To keep API consistent the units should be the same for both cases, just the
resolution should change.
Signed-off-by: Stephen Hemminger <shemminger@linux-foundation.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
None of the existing TCP congestion controls use the rtt value pased
in the ca_ops->cong_avoid interface. Which is lucky because seq_rtt
could have been -1 when handling a duplicate ack.
Signed-off-by: Stephen Hemminger <shemminger@linux-foundation.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
Commit 164891aadf broke RTT
sampling of congestion control modules. Inaccurate timestamps
could be fed to them without providing any way for them to
identify such cases. Previously RTT sampler was called only if
FLAG_RETRANS_DATA_ACKED was not set filtering inaccurate
timestamps nicely. In addition, the new behavior could give an
invalid timestamp (zero) to RTT sampler if only skbs with
TCPCB_RETRANS were ACKed. This solves both problems.
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@helsinki.fi>
Signed-off-by: David S. Miller <davem@davemloft.net>
To avoid raw division, use ktime_to_timeval() to get usec.
Signed-off-by: YOSHIFUJI Hideaki <yoshfuji@linux-ipv6.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
Do some simple changes to make congestion control API faster/cleaner.
* use ktime_t rather than timeval
* merge rtt sampling into existing ack callback
this means one indirect call versus two per ack.
* use flags bits to store options/settings
Signed-off-by: Stephen Hemminger <shemminger@linux-foundation.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
config.h is automatically included by kbuild these days.
Signed-off-by: Dave Jones <davej@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Many of the TCP congestion methods all just use ssthresh
as the minimum congestion window on decrease. Rather than
duplicating the code, just have that be the default if that
handle in the ops structure is not set.
Minor behaviour change to TCP compound. It probably wants
to use this (ssthresh) as lower bound, rather than ssthresh/2
because the latter causes undershoot on loss.
Signed-off-by: Stephen Hemminger <shemminger@osdl.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
TCP Veno module is a new congestion control module to improve TCP
performance over wireless networks. The key innovation in TCP Veno is
the enhancement of TCP Reno/Sack congestion control algorithm by using
the estimated state of a connection based on TCP Vegas. This scheme
significantly reduces "blind" reduction of TCP window regardless of
the cause of packet loss.
This work is based on the research paper "TCP Veno: TCP Enhancement
for Transmission over Wireless Access Networks." C. P. Fu, S. C. Liew,
IEEE Journal on Selected Areas in Communication, Feb. 2003.
Original paper and many latest research works on veno:
http://www.ntu.edu.sg/home/ascpfu/veno/veno.html
Signed-off-by: Bin Zhou <zhou0022@ntu.edu.sg>
Cheng Peng Fu <ascpfu@ntu.edu.sg>
Signed-off-by: Stephen Hemminger <shemminger@osdl.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
