Filter TCP connections to SO_REUSEPORT_LB listen sockets by NUMA domain

In order to efficiently serve web traffic on a NUMA
machine, one must avoid as many NUMA domain crossings as
possible. With SO_REUSEPORT_LB, a number of workers can share a
listen socket. However, even if a worker sets affinity to a core
or set of cores on a NUMA domain, it will receive connections
associated with all NUMA domains in the system. This will lead to
cross-domain traffic when the server writes to the socket or
calls sendfile(), and memory is allocated on the server's local
NUMA node, but transmitted on the NUMA node associated with the
TCP connection. Similarly, when the server reads from the socket,
he will likely be reading memory allocated on the NUMA domain
associated with the TCP connection.

This change provides a new socket ioctl, TCP_REUSPORT_LB_NUMA. A
server can now tell the kernel to filter traffic so that only
incoming connections associated with the desired NUMA domain are
given to the server. (Of course, in the case where there are no
servers sharing the listen socket on some domain, then as a
fallback, traffic will be hashed as normal to all servers sharing
the listen socket regardless of domain). This allows a server to
deal only with traffic that is local to its NUMA domain, and
avoids cross-domain traffic in most cases.

This patch, and a corresponding small patch to nginx to use
TCP_REUSPORT_LB_NUMA allows us to serve 190Gb/s of kTLS encrypted
https media content from dual-socket Xeons with only 13% (as
measured by pcm.x) cross domain traffic on the memory controller.

Reviewed by:	jhb, bz (earlier version), bcr (man page)
Tested by: gonzo
Sponsored by:	Netfix
Differential Revision:	https://reviews.freebsd.org/D21636

1 files changed, 16 insertions, 1 deletions

diff --git a/share/man/man4/tcp.4 b/share/man/man4/tcp.4
index b046c56ef4e6..24b2e2d24d19 100644
--- a/share/man/man4/tcp.4
+++ b/share/man/man4/tcp.4
@@ -34,7 +34,7 @@
 .\"     From: @(#)tcp.4	8.1 (Berkeley) 6/5/93
 .\" $FreeBSD$
 .\"
-.Dd November 25, 2020
+.Dd December 19, 2020
 .Dt TCP 4
 .Os
 .Sh NAME
@@ -314,6 +314,21 @@ Enable in-kernel TLS for data read from this socket.
 See
 .Xr ktls 4
 for more details.
+.It Dv TCP_REUSPORT_LB_NUMA
+Changes NUMA affinity filtering for an established TCP listen
+socket.
+This option takes a single integer argument which specifies
+the NUMA domain to filter on for this listen socket.
+The argument can also have the follwing special values:
+.Bl -tag -width "Dv TCP_REUSPORT_LB_NUMA"
+.It Dv TCP_REUSPORT_LB_NUMA_NODOM
+Remove NUMA filtering for this listen socket.
+.It Dv TCP_REUSPORT_LB_NUMA_CURDOM
+Filter traffic associated with the domain where the calling thread is
+currently executing.
+This is typically used after a process or thread inherits a listen
+socket from its parent, and sets its CPU affinity to a particular core.
+.El
 .El
 .Pp
 The option level for the