ovs/lib/dpif-netlink-unixctl.man

.SS "DPIF-NETLINK COMMANDS"
These commands are used to expose internal information of the "dpif-netlink"
kernel space datapath.
.
.IP "\fBdpif-netlink/dispatch-mode\fR"
Displays the "dispatch-mode" for all datapaths.
dpif-netlink: Introduce per-cpu upcall dispatch. The Open vSwitch kernel module uses the upcall mechanism to send packets from kernel space to user space when it misses in the kernel space flow table. The upcall sends packets via a Netlink socket. Currently, a Netlink socket is created for every vport. In this way, there is a 1:1 mapping between a vport and a Netlink socket. When a packet is received by a vport, if it needs to be sent to user space, it is sent via the corresponding Netlink socket. This mechanism, with various iterations of the corresponding user space code, has seen some limitations and issues: * On systems with a large number of vports, there is correspondingly a large number of Netlink sockets which can limit scaling. (https://bugzilla.redhat.com/show_bug.cgi?id=1526306) * Packet reordering on upcalls. (https://bugzilla.redhat.com/show_bug.cgi?id=1844576) * A thundering herd issue. (https://bugzilla.redhat.com/show_bug.cgi?id=1834444) This patch introduces an alternative, feature-negotiated, upcall mode using a per-cpu dispatch rather than a per-vport dispatch. In this mode, the Netlink socket to be used for the upcall is selected based on the CPU of the thread that is executing the upcall. In this way, it resolves the issues above as: a) The number of Netlink sockets scales with the number of CPUs rather than the number of vports. b) Ordering per-flow is maintained as packets are distributed to CPUs based on mechanisms such as RSS and flows are distributed to a single user space thread. c) Packets from a flow can only wake up one user space thread. Reported-at: https://bugzilla.redhat.com/1844576 Signed-off-by: Mark Gray <mark.d.gray@redhat.com> Acked-by: Flavio Leitner <fbl@sysclose.org> Acked-by: Aaron Conole <aconole@redhat.com> Signed-off-by: Ilya Maximets <i.maximets@ovn.org> 2021-07-16 06:17:36 -04:00			`.SS "DPIF-NETLINK COMMANDS"`
			`These commands are used to expose internal information of the "dpif-netlink"`
			`kernel space datapath.`
			`.`
			`.IP "\fBdpif-netlink/dispatch-mode\fR"`
			`Displays the "dispatch-mode" for all datapaths.`