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tcp: clarify tcp_congestion_ops functions comments

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The optional and required hints in the tcp_congestion_ops are information
for the user of this interface to signalize its importance when
implementing these functions.

However, cong_avoid comment incorrectly tells that it is required,
in reality congestion control must provide one of either cong_avoid or
cong_control.

In addition, min_tso_segs has not had any comment optional/required
hints. So mark it as optional since it is used only in BBR.

Co-developed-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: Daniel Sedlak <daniel.sedlak@cdn77.com>
Link: https://patch.msgid.link/20260105115533.1151442-1-daniel.sedlak@cdn77.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Daniel Sedlak
2026-01-05 12:55:33 +01:00
committed by Jakub Kicinski
parent f66086798f
commit 55ffb0b14a
1 changed files with 19 additions and 10 deletions
Download Patch File Download Diff File Expand all files Collapse all files

29
include/net/tcp.h
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@@ -1243,12 +1243,27 @@ struct rate_sample {
struct tcp_congestion_ops {
/* fast path fields are put first to fill one cache line */
/* A congestion control (CC) must provide one of either:
*
* (a) a cong_avoid function, if the CC wants to use the core TCP
* stack's default functionality to implement a "classic"
* (Reno/CUBIC-style) response to packet loss, RFC3168 ECN,
* idle periods, pacing rate computations, etc.
*
* (b) a cong_control function, if the CC wants custom behavior and
* complete control of all congestion control behaviors.
*/
/* (a) "classic" response: calculate new cwnd.
*/
void (*cong_avoid)(struct sock *sk, u32 ack, u32 acked);
/* (b) "custom" response: call when packets are delivered to update
* cwnd and pacing rate, after all the ca_state processing.
*/
void (*cong_control)(struct sock *sk, u32 ack, int flag, const struct rate_sample *rs);
/* return slow start threshold (required) */
u32 (*ssthresh)(struct sock *sk);
/* do new cwnd calculation (required) */
void (*cong_avoid)(struct sock *sk, u32 ack, u32 acked);
/* call before changing ca_state (optional) */
void (*set_state)(struct sock *sk, u8 new_state);
@@ -1261,15 +1276,9 @@ struct tcp_congestion_ops {
/* hook for packet ack accounting (optional) */
void (*pkts_acked)(struct sock *sk, const struct ack_sample *sample);
/* override sysctl_tcp_min_tso_segs */
/* override sysctl_tcp_min_tso_segs (optional) */
u32 (*min_tso_segs)(struct sock *sk);
/* call when packets are delivered to update cwnd and pacing rate,
* after all the ca_state processing. (optional)
*/
void (*cong_control)(struct sock *sk, u32 ack, int flag, const struct rate_sample *rs);
/* new value of cwnd after loss (required) */
u32 (*undo_cwnd)(struct sock *sk);
/* returns the multiplier used in tcp_sndbuf_expand (optional) */