linux-toradex.git/net/ipv4/tcp_cubic.c, branch v3.2.63

tcp_cubic: fix the range of delayed_ack

2014-06-09T12:28:58+00:00

[ Upstream commit 0cda345d1b2201dd15591b163e3c92bad5191745 ]

commit b9f47a3aaeab (tcp_cubic: limit delayed_ack ratio to prevent
divide error) try to prevent divide error, but there is still a little
chance that delayed_ack can reach zero. In case the param cnt get
negative value, then ratio+cnt would overflow and may happen to be zero.
As a result, min(ratio, ACK_RATIO_LIMIT) will calculate to be zero.

In some old kernels, such as 2.6.32, there is a bug that would
pass negative param, which then ultimately leads to this divide error.

commit 5b35e1e6e9c (tcp: fix tcp_trim_head() to adjust segment count
with skb MSS) fixed the negative param issue. However,
it's safe that we fix the range of delayed_ack as well,
to make sure we do not hit a divide by zero.

CC: Stephen Hemminger 
Signed-off-by: Liu Yu 
Signed-off-by: Eric Dumazet 
Acked-by: Neal Cardwell 
Signed-off-by: David S. Miller 
Signed-off-by: Ben Hutchings

tcp: cubic: fix bug in bictcp_acked()

2013-10-26T20:05:56+00:00

[ Upstream commit cd6b423afd3c08b27e1fed52db828ade0addbc6b ]

While investigating about strange increase of retransmit rates
on hosts ~24 days after boot, Van found hystart was disabled
if ca->epoch_start was 0, as following condition is true
when tcp_time_stamp high order bit is set.

(s32)(tcp_time_stamp - ca->epoch_start) < HZ

Quoting Van :

 At initialization & after every loss ca->epoch_start is set to zero so
 I believe that the above line will turn off hystart as soon as the 2^31
 bit is set in tcp_time_stamp & hystart will stay off for 24 days.
 I think we've observed that cubic's restart is too aggressive without
 hystart so this might account for the higher drop rate we observe.

Diagnosed-by: Van Jacobson 
Signed-off-by: Eric Dumazet 
Cc: Neal Cardwell 
Cc: Yuchung Cheng 
Acked-by: Neal Cardwell 
Signed-off-by: David S. Miller 
Signed-off-by: Ben Hutchings

tcp: cubic: fix overflow error in bictcp_update()

2013-10-26T20:05:55+00:00

[ Upstream commit 2ed0edf9090bf4afa2c6fc4f38575a85a80d4b20 ]

commit 17a6e9f1aa9 ("tcp_cubic: fix clock dependency") added an
overflow error in bictcp_update() in following code :

/* change the unit from HZ to bictcp_HZ */
t = ((tcp_time_stamp + msecs_to_jiffies(ca->delay_min>>3) -
      ca->epoch_start) << BICTCP_HZ) / HZ;

Because msecs_to_jiffies() being unsigned long, compiler does
implicit type promotion.

We really want to constrain (tcp_time_stamp - ca->epoch_start)
to a signed 32bit value, or else 't' has unexpected high values.

This bugs triggers an increase of retransmit rates ~24 days after
boot [1], as the high order bit of tcp_time_stamp flips.

[1] for hosts with HZ=1000

Big thanks to Van Jacobson for spotting this problem.

Diagnosed-by: Van Jacobson 
Signed-off-by: Eric Dumazet 
Cc: Neal Cardwell 
Cc: Yuchung Cheng 
Cc: Stephen Hemminger 
Acked-by: Neal Cardwell 
Signed-off-by: David S. Miller 
Signed-off-by: Ben Hutchings

tcp_cubic: limit delayed_ack ratio to prevent divide error

2011-05-08T22:51:57+00:00

TCP Cubic keeps a metric that estimates the amount of delayed
acknowledgements to use in adjusting the window. If an abnormally
large number of packets are acknowledged at once, then the update
could wrap and reach zero. This kind of ACK could only
happen when there was a large window and huge number of
ACK's were lost.

This patch limits the value of delayed ack ratio. The choice of 32
is just a conservative value since normally it should be range of
1 to 4 packets.

Signed-off-by: Stephen Hemminger 
Signed-off-by: David S. Miller

Merge branch 'master' of master.kernel.org:/pub/scm/linux/kernel/git/davem/net-2.6

2011-03-15T22:15:17+00:00

tcp_cubic: fix low utilization of CUBIC with HyStart

2011-03-14T22:54:42+00:00

HyStart sets the initial exit point of slow start.
Suppose that HyStart exits at 0.5BDP in a BDP network and no history exists.
If the BDP of a network is large, CUBIC's initial cwnd growth may be
too conservative to utilize the link.
CUBIC increases the cwnd 20% per RTT in this case.

Signed-off-by: Sangtae Ha 
Acked-by: Stephen Hemminger 
Signed-off-by: David S. Miller

tcp_cubic: make the delay threshold of HyStart less sensitive

2011-03-14T22:54:42+00:00

Make HyStart less sensitive to abrupt delay variations due to buffer bloat.

Signed-off-by: Sangtae Ha 
Acked-by: Stephen Hemminger 
Reported-by: Lucas Nussbaum 
Signed-off-by: David S. Miller

tcp_cubic: enable high resolution ack time if needed

2011-03-14T22:54:40+00:00

This is a refined version of an earlier patch by Lucas Nussbaum.
Cubic needs RTT values in milliseconds. If HZ < 1000 then
the values will be too coarse.

Signed-off-by: Stephen Hemminger 
Reported-by: Lucas Nussbaum 
Signed-off-by: David S. Miller

tcp_cubic: fix clock dependency

2011-03-14T22:54:39+00:00

The hystart code was written with assumption that HZ=1000.
Replace the use of jiffies with bictcp_clock as a millisecond
real time clock.

Signed-off-by: Stephen Hemminger 
Reported-by: Lucas Nussbaum 
Signed-off-by: David S. Miller

tcp_cubic: make ack train delta value a parameter

2011-03-14T22:54:39+00:00

Make the spacing between ACK's that indicates a train a tuneable
value like other hystart values.

Signed-off-by: Stephen Hemminger 
Signed-off-by: David S. Miller