]> git.baikalelectronics.ru Git - kernel.git/commit
dctcp: avoid bogus doubling of cwnd after loss
authorFlorian Westphal <fw@strlen.de>
Fri, 28 Oct 2016 16:43:11 +0000 (18:43 +0200)
committerDavid S. Miller <davem@davemloft.net>
Mon, 31 Oct 2016 19:16:28 +0000 (15:16 -0400)
commitfa5d325effbf0ef4533fba5b72458bf579aac954
tree133ffe80d56955a590a8f3d1dfad24e34f61aef6
parent38b3c9ed084e2a322e76745c9d723961d9cd06d0
dctcp: avoid bogus doubling of cwnd after loss

If a congestion control module doesn't provide .undo_cwnd function,
tcp_undo_cwnd_reduction() will set cwnd to

   tp->snd_cwnd = max(tp->snd_cwnd, tp->snd_ssthresh << 1);

... which makes sense for reno (it sets ssthresh to half the current cwnd),
but it makes no sense for dctcp, which sets ssthresh based on the current
congestion estimate.

This can cause severe growth of cwnd (eventually overflowing u32).

Fix this by saving last cwnd on loss and restore cwnd based on that,
similar to cubic and other algorithms.

Fixes: 31efce77126834 ("net: tcp: add DCTCP congestion control algorithm")
Cc: Lawrence Brakmo <brakmo@fb.com>
Cc: Andrew Shewmaker <agshew@gmail.com>
Cc: Glenn Judd <glenn.judd@morganstanley.com>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: David S. Miller <davem@davemloft.net>
net/ipv4/tcp_dctcp.c