diff mbox series

[net-next] tcp: improve PRR loss recovery

Message ID 20220519003410.2531936-1-ycheng@google.com (mailing list archive)
State Accepted
Commit 9ad084d666194c20a30e3589cbfaf971dae55c24
Delegated to: Netdev Maintainers
Headers show
Series [net-next] tcp: improve PRR loss recovery | expand

Checks

Context Check Description
netdev/tree_selection success Clearly marked for net-next
netdev/fixes_present success Fixes tag not required for -next series
netdev/subject_prefix success Link
netdev/cover_letter success Single patches do not need cover letters
netdev/patch_count success Link
netdev/header_inline success No static functions without inline keyword in header files
netdev/build_32bit success Errors and warnings before: 3 this patch: 3
netdev/cc_maintainers warning 4 maintainers not CCed: yoshfuji@linux-ipv6.org dsahern@kernel.org pabeni@redhat.com kuba@kernel.org
netdev/build_clang success Errors and warnings before: 10 this patch: 10
netdev/module_param success Was 0 now: 0
netdev/verify_signedoff success Signed-off-by tag matches author and committer
netdev/verify_fixes success No Fixes tag
netdev/build_allmodconfig_warn success Errors and warnings before: 3 this patch: 3
netdev/checkpatch fail ERROR: Unrecognized email address: 'Neal Cardwell <ncardwell@google.com'
netdev/kdoc success Errors and warnings before: 0 this patch: 0
netdev/source_inline success Was 0 now: 0

Commit Message

Yuchung Cheng May 19, 2022, 12:34 a.m. UTC 
This patch improves TCP PRR loss recovery behavior for a corner
case. Previously during PRR conservation-bound mode, it strictly
sends the amount equals to the amount newly acked or s/acked.

The patch changes s.t. PRR may send additional amount that was banked
previously (e.g. application-limited) in the conservation-bound
mode, similar to the slow-start mode. This unifies and simplifies the
algorithm further and may improve the recovery latency. This change
still follow the general packet conservation design principle and
always keep inflight/cwnd below the slow start threshold set
by the congestion control module.

PRR is described in RFC 6937. We'll include this change in the
latest revision rfc6937-bis as well.

Reported-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: Yuchung Cheng <ycheng@google.com>
Signed-off-by: Neal Cardwell <ncardwell@google.com
Signed-off-by: Eric Dumazet <edumazet@google.com>
---
 net/ipv4/tcp_input.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

Comments

patchwork-bot+netdevbpf@kernel.org May 20, 2022, 2:10 a.m. UTC | #1 
Hello:

This patch was applied to netdev/net-next.git (master)
by Jakub Kicinski <kuba@kernel.org>:

On Wed, 18 May 2022 17:34:10 -0700 you wrote:
> This patch improves TCP PRR loss recovery behavior for a corner
> case. Previously during PRR conservation-bound mode, it strictly
> sends the amount equals to the amount newly acked or s/acked.
> 
> The patch changes s.t. PRR may send additional amount that was banked
> previously (e.g. application-limited) in the conservation-bound
> mode, similar to the slow-start mode. This unifies and simplifies the
> algorithm further and may improve the recovery latency. This change
> still follow the general packet conservation design principle and
> always keep inflight/cwnd below the slow start threshold set
> by the congestion control module.
> 
> [...]

Here is the summary with links:
  - [net-next] tcp: improve PRR loss recovery
    https://git.kernel.org/netdev/net-next/c/9ad084d66619

You are awesome, thank you!
diff mbox series

Patch

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 97cfcd85f84e..3231af73e430 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -2620,12 +2620,12 @@  void tcp_cwnd_reduction(struct sock *sk, int newly_acked_sacked, int newly_lost,
 		u64 dividend = (u64)tp->snd_ssthresh * tp->prr_delivered +
 			       tp->prior_cwnd - 1;
 		sndcnt = div_u64(dividend, tp->prior_cwnd) - tp->prr_out;
-	} else if (flag & FLAG_SND_UNA_ADVANCED && !newly_lost) {
-		sndcnt = min_t(int, delta,
-			       max_t(int, tp->prr_delivered - tp->prr_out,
-				     newly_acked_sacked) + 1);
 	} else {
-		sndcnt = min(delta, newly_acked_sacked);
+		sndcnt = max_t(int, tp->prr_delivered - tp->prr_out,
+			       newly_acked_sacked);
+		if (flag & FLAG_SND_UNA_ADVANCED && !newly_lost)
+			sndcnt++;
+		sndcnt = min(delta, sndcnt);
 	}
 	/* Force a fast retransmit upon entering fast recovery */
 	sndcnt = max(sndcnt, (tp->prr_out ? 0 : 1));