From mboxrd@z Thu Jan 1 00:00:00 1970 From: Neal Cardwell Subject: [PATCH net-next] tcp_bbr: update comments to reflect pacing_margin_percent Date: Thu, 8 Nov 2018 21:54:00 -0500 Message-ID: <20181109025400.38021-1-ncardwell@google.com> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Cc: netdev@vger.kernel.org, Neal Cardwell , Yuchung Cheng , Soheil Hassas Yeganeh , Eric Dumazet To: David Miller Return-path: Received: from mail-yw1-f73.google.com ([209.85.161.73]:39661 "EHLO mail-yw1-f73.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727349AbeKIMck (ORCPT ); Fri, 9 Nov 2018 07:32:40 -0500 Received: by mail-yw1-f73.google.com with SMTP id 4-v6so935198ywb.6 for ; Thu, 08 Nov 2018 18:54:06 -0800 (PST) Sender: netdev-owner@vger.kernel.org List-ID: Recently, in commit ab408b6dc744 ("tcp: switch tcp and sch_fq to new earliest departure time model"), the TCP BBR code switched to a new approach of using an explicit bbr_pacing_margin_percent for shaving a pacing rate "haircut", rather than the previous implict approach. Update an old comment to reflect the new approach. Signed-off-by: Neal Cardwell Signed-off-by: Yuchung Cheng Signed-off-by: Soheil Hassas Yeganeh Signed-off-by: Eric Dumazet --- net/ipv4/tcp_bbr.c | 15 +++++++-------- 1 file changed, 7 insertions(+), 8 deletions(-) diff --git a/net/ipv4/tcp_bbr.c b/net/ipv4/tcp_bbr.c index 9277abdd822a0..0f497fc49c3fe 100644 --- a/net/ipv4/tcp_bbr.c +++ b/net/ipv4/tcp_bbr.c @@ -128,7 +128,12 @@ static const u32 bbr_probe_rtt_mode_ms = 200; /* Skip TSO below the following bandwidth (bits/sec): */ static const int bbr_min_tso_rate = 1200000; -/* Pace at ~1% below estimated bw, on average, to reduce queue at bottleneck. */ +/* Pace at ~1% below estimated bw, on average, to reduce queue at bottleneck. + * In order to help drive the network toward lower queues and low latency while + * maintaining high utilization, the average pacing rate aims to be slightly + * lower than the estimated bandwidth. This is an important aspect of the + * design. + */ static const int bbr_pacing_margin_percent = 1; /* We use a high_gain value of 2/ln(2) because it's the smallest pacing gain @@ -247,13 +252,7 @@ static void bbr_init_pacing_rate_from_rtt(struct sock *sk) sk->sk_pacing_rate = bbr_bw_to_pacing_rate(sk, bw, bbr_high_gain); } -/* Pace using current bw estimate and a gain factor. In order to help drive the - * network toward lower queues while maintaining high utilization and low - * latency, the average pacing rate aims to be slightly (~1%) lower than the - * estimated bandwidth. This is an important aspect of the design. In this - * implementation this slightly lower pacing rate is achieved implicitly by not - * including link-layer headers in the packet size used for the pacing rate. - */ +/* Pace using current bw estimate and a gain factor. */ static void bbr_set_pacing_rate(struct sock *sk, u32 bw, int gain) { struct tcp_sock *tp = tcp_sk(sk); -- 2.19.1.930.g4563a0d9d0-goog