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tcp_bbr: update comments to reflect pacing_margin_percent 

Recently, in commit ab408b6dc7 ("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 <ncardwell@google.com>
Signed-off-by: Yuchung Cheng <ycheng@google.com>
Signed-off-by: Soheil Hassas Yeganeh <soheil@google.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Neal Cardwell 2018-11-08 21:54:00 -05:00 committed by David S. Miller
parent dd00e06d3b
commit 1106a5ade1
1 changed files with 7 additions and 8 deletions
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15
net/ipv4/tcp_bbr.c
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@ -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);