From: Luke Hsiao <lukehs...@google.com>
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 <lukehs...@google.com>
Acked-by: Soheil Hassas Yeganeh <soh...@google.com>
Acked-by: Neal Cardwell <ncardw...@google.com>
Acked-by: Priyaranjan Jha <priyar...@google.com>
---
net/ipv4/tcp_bbr.c | 6 ++++--
1 file 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;
--
2.23.0.187.g17f5b7556c-goog
