diff options
| author | Luke Hsiao <lukehsiao@google.com> | 2019-08-29 10:02:44 -0400 |
|---|---|---|
| committer | David S. Miller <davem@davemloft.net> | 2019-08-30 15:08:15 -0700 |
| commit | de8e1beb191912f94bcab46e72f247daaf664d15 (patch) | |
| tree | 3768bab6151d6f43e9f0d05f3d86c285b62ef5f9 | |
| parent | fa730a3bb9d35fa2289a2b6a0a4846154873f6f2 (diff) | |
tcp_bbr: clarify that bbr_bdp() rounds up in comments
This explicitly clarifies that bbr_bdp() returns the rounded-up value of
the bandwidth-delay product and why in the comments.
Signed-off-by: Luke Hsiao <lukehsiao@google.com>
Acked-by: Soheil Hassas Yeganeh <soheil@google.com>
Acked-by: Neal Cardwell <ncardwell@google.com>
Acked-by: Priyaranjan Jha <priyarjha@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
| -rw-r--r-- | net/ipv4/tcp_bbr.c | 6 |
1 files changed, 4 insertions, 2 deletions
diff --git a/net/ipv4/tcp_bbr.c b/net/ipv4/tcp_bbr.c index 56be7d27f208..95b59540eee1 100644 --- a/net/ipv4/tcp_bbr.c +++ b/net/ipv4/tcp_bbr.c @@ -346,7 +346,7 @@ static void bbr_cwnd_event(struct sock *sk, enum tcp_ca_event event) /* Calculate bdp based on min RTT and the estimated bottleneck bandwidth: * - * bdp = bw * min_rtt * gain + * bdp = ceil(bw * min_rtt * gain) * * The key factor, gain, controls the amount of queue. While a small gain * builds a smaller queue, it becomes more vulnerable to noise in RTT @@ -370,7 +370,9 @@ static u32 bbr_bdp(struct sock *sk, u32 bw, int gain) w = (u64)bw * bbr->min_rtt_us; - /* Apply a gain to the given value, then remove the BW_SCALE shift. */ + /* Apply a gain to the given value, remove the BW_SCALE shift, and + * round the value up to avoid a negative feedback loop. + */ bdp = (((w * gain) >> BBR_SCALE) + BW_UNIT - 1) / BW_UNIT; return bdp; |