a9ec54d1b0
The VRF driver allows users to implement device based features for an entire domain. For example, a qdisc or netfilter rules can be attached to a VRF device or tcpdump can be used to view packets for all devices in the L3 domain. The device-based features come with a performance penalty, most notably in the Tx path. The VRF driver uses the l3mdev_l3_out hook to switch the dst on an skb to its private dst. This allows the skb to traverse the xmit stack with the device set to the VRF device which in turn enables the netfilter and qdisc features. The VRF driver then performs the FIB lookup again and reinserts the packet. This patch avoids the redirect for IPv6 packets if a qdisc has not been attached to a VRF device which is the default config. In this case the netfilter hooks and network taps are directly traversed in the l3mdev_l3_out handler. If a qdisc is attached to a VRF device, then the redirect using the vrf dst is done. Additional overhead is removed by only checking packet taps if a socket is open on the device (vrf_dev->ptype_all list is not empty). Packet sockets bound to any device will still get a copy of the packet via the real ingress or egress interface. The end result of this change is a decrease in the overhead of VRF for the default, baseline case (ie., no netfilter rules, no packet sockets, no qdisc) from a +3% improvement for UDP which has a lookup per packet (VRF being better than no l3mdev) to ~2% loss for TCP_CRR which connects a socket for each request-response. Signed-off-by: David Ahern <dsa@cumulusnetworks.com> Signed-off-by: David S. Miller <davem@davemloft.net> |
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README
Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. Please read the Documentation/process/changes.rst file, as it contains the requirements for building and running the kernel, and information about the problems which may result by upgrading your kernel.