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authorNeal Cardwell <ncardwell@google.com>2015-03-10 17:17:03 -0400
committerDavid S. Miller <davem@davemloft.net>2015-03-11 16:51:51 -0400
commit9949afa42be0b76f5832db112ce51bb6b35b2abb (patch)
treedded55a25200f202f9904369f39ccad9769da00d /net/ipv4/tcp_cong.c
parent366c1bd191c49380d81b15b96cf7d4e3528a82a2 (diff)
downloadlinux-9949afa42be0b76f5832db112ce51bb6b35b2abb.tar.bz2
tcp: fix tcp_cong_avoid_ai() credit accumulation bug with decreases in w
The recent change to tcp_cong_avoid_ai() to handle stretch ACKs introduced a bug where snd_cwnd_cnt could accumulate a very large value while w was large, and then if w was reduced snd_cwnd could be incremented by a large delta, leading to a large burst and high packet loss. This was tickled when CUBIC's bictcp_update() sets "ca->cnt = 100 * cwnd". This bug crept in while preparing the upstream version of 814d488c6126. Testing: This patch has been tested in datacenter netperf transfers and live youtube.com and google.com servers. Fixes: 814d488c6126 ("tcp: fix the timid additive increase on stretch ACKs") Signed-off-by: Neal Cardwell <ncardwell@google.com> Signed-off-by: Yuchung Cheng <ycheng@google.com> Signed-off-by: Eric Dumazet <edumazet@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'net/ipv4/tcp_cong.c')
-rw-r--r--net/ipv4/tcp_cong.c6
1 files changed, 6 insertions, 0 deletions
diff --git a/net/ipv4/tcp_cong.c b/net/ipv4/tcp_cong.c
index d694088214cd..62856e185a93 100644
--- a/net/ipv4/tcp_cong.c
+++ b/net/ipv4/tcp_cong.c
@@ -378,6 +378,12 @@ EXPORT_SYMBOL_GPL(tcp_slow_start);
*/
void tcp_cong_avoid_ai(struct tcp_sock *tp, u32 w, u32 acked)
{
+ /* If credits accumulated at a higher w, apply them gently now. */
+ if (tp->snd_cwnd_cnt >= w) {
+ tp->snd_cwnd_cnt = 0;
+ tp->snd_cwnd++;
+ }
+
tp->snd_cwnd_cnt += acked;
if (tp->snd_cwnd_cnt >= w) {
u32 delta = tp->snd_cwnd_cnt / w;