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tcp: enable LRD by default 

Lost Retransmission Detection was added as a
feature in May 2021, but disabled by default.

Enabling the feature by default to reduce the
flow completion time by avoiding RTOs when
retransmissions get lost too.

Reviewed By:           tuexen, #transport, zlei
MFC after:             10 weeks
Sponsored by:          NetApp, Inc.
Differential Revision: https://reviews.freebsd.org/D42845
This commit is contained in:
Richard Scheffenegger 2023-11-30 05:33:50 +01:00
parent 839999e7ef
commit 34c45bc6a3
2 changed files with 3 additions and 3 deletions
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4
share/man/man4/tcp.4
View File

@ -31,7 +31,7 @@
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
.\" SUCH DAMAGE. .\" SUCH DAMAGE.
.\" .\"
.Dd November 17, 2023 .Dd November 30, 2023
.Dt TCP 4 .Dt TCP 4
.Os .Os
.Sh NAME .Sh NAME
@ -465,7 +465,7 @@ Maximum amount of time, in milliseconds, before a delayed ACK is sent.
.It Va delayed_ack .It Va delayed_ack
Delay ACK to try and piggyback it onto a data packet or another ACK. Delay ACK to try and piggyback it onto a data packet or another ACK.
.It Va do_lrd .It Va do_lrd
Enable Lost Retransmission Detection for SACK-enabled sessions, disabled by Enable Lost Retransmission Detection for SACK-enabled sessions, enabled by
default. default.
Under severe congestion, a retransmission can be lost which then leads to a Under severe congestion, a retransmission can be lost which then leads to a
mandatory Retransmission Timeout (RTO), followed by slow-start. mandatory Retransmission Timeout (RTO), followed by slow-start.

2
sys/netinet/tcp_input.c
View File

@ -162,7 +162,7 @@ SYSCTL_INT(_net_inet_tcp, OID_AUTO, do_prr, CTLFLAG_VNET | CTLFLAG_RW,
&VNET_NAME(tcp_do_prr), 1, &VNET_NAME(tcp_do_prr), 1,
"Enable Proportional Rate Reduction per RFC 6937"); "Enable Proportional Rate Reduction per RFC 6937");
VNET_DEFINE(int, tcp_do_lrd) = 0; VNET_DEFINE(int, tcp_do_lrd) = 1;
SYSCTL_INT(_net_inet_tcp, OID_AUTO, do_lrd, CTLFLAG_VNET | CTLFLAG_RW, SYSCTL_INT(_net_inet_tcp, OID_AUTO, do_lrd, CTLFLAG_VNET | CTLFLAG_RW,
&VNET_NAME(tcp_do_lrd), 1, &VNET_NAME(tcp_do_lrd), 1,
"Perform Lost Retransmission Detection"); "Perform Lost Retransmission Detection");