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Commit 1106a5ad authored by Neal Cardwell's avatar Neal Cardwell Committed by David S. Miller
Browse files

tcp_bbr: update comments to reflect pacing_margin_percent 



Recently, in commit ab408b6d ("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: default avatarNeal Cardwell <ncardwell@google.com>
Signed-off-by: default avatarYuchung Cheng <ycheng@google.com>
Signed-off-by: default avatarSoheil Hassas Yeganeh <soheil@google.com>
Signed-off-by: default avatarEric Dumazet <edumazet@google.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent dd00e06d

net/ipv4/tcp_bbr.c

+7 −8
Original line number Diff line number Diff line
@@ -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);