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tcp: enable LRD by default

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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
.\" SUCH DAMAGE.
.\"
.Dd November 17, 2023
.Dd November 30, 2023
.Dt TCP 4
.Os
.Sh NAME
@ -465,7 +465,7 @@ Maximum amount of time, in milliseconds, before a delayed ACK is sent.
.It Va delayed_ack
Delay ACK to try and piggyback it onto a data packet or another ACK.
.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.
Under severe congestion, a retransmission can be lost which then leads to a
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,
"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,
&VNET_NAME(tcp_do_lrd), 1,
"Perform Lost Retransmission Detection");