| Message ID | 1426022224-28793-1-git-send-email-ncardwell@google.com |
|---|---|
| State | Accepted, archived |
| Delegated to: | David Miller |
| Headers | show |
From: Neal Cardwell <ncardwell@google.com> Date: Tue, 10 Mar 2015 17:17:03 -0400 > 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> Applied. -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/net/ipv4/tcp_cong.c b/net/ipv4/tcp_cong.c index d694088..62856e1 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;
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> --- net/ipv4/tcp_cong.c | 6 ++++++ 1 file changed, 6 insertions(+)