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Diffstat (limited to 'src/plugins/af_xdp/af_xdp_doc.md')
| -rw-r--r-- | src/plugins/af_xdp/af_xdp_doc.md | 28 |
1 files changed, 27 insertions, 1 deletions
diff --git a/src/plugins/af_xdp/af_xdp_doc.md b/src/plugins/af_xdp/af_xdp_doc.md index 7d83d712918..f5859dbb901 100644 --- a/src/plugins/af_xdp/af_xdp_doc.md +++ b/src/plugins/af_xdp/af_xdp_doc.md @@ -12,11 +12,15 @@ Under development: it should work, but has not been thoroughly tested. - custom eBPF program - polling, interrupt and adaptive mode -## Limitations +## Known limitations + +### MTU Because of AF_XDP restrictions, the MTU is limited to below PAGE_SIZE (4096-bytes on most systems) minus 256-bytes, and they are additional limitations depending upon specific Linux device drivers. As a rule of thumb, a MTU of 3000-bytes or less should be safe. + +### Number of buffers Furthermore, upon UMEM creation, the kernel allocates a physically-contiguous structure, whose size is proportional to the number of 4KB pages contained in the UMEM. That allocation might fail when @@ -25,7 +29,29 @@ controlled with the `buffers { buffers-per-numa }` configuration option. Finally, note that because of this limitation, this plugin is unlikely to be compatible with the use of 1GB hugepages. +### Interrupt mode +Interrupt and adaptive mode are supported but is limited by default to single +threaded (no worker) configurations because of a kernel limitation prior to +5.6. You can bypass the limitation at interface creation time by adding the +`no-syscall-lock` parameter, but you must be sure that your kernel can +support it, otherwise you will experience double-frees. +See +https://lore.kernel.org/bpf/BYAPR11MB365382C5DB1E5FCC53242609C1549@BYAPR11MB3653.namprd11.prod.outlook.com/ +for more details. + +### Mellanox +When setting the number of queues on Mellanox NIC with `ethtool -L`, you must +use twice the amount of configured queues: it looks like the Linux driver will +create separate RX queues and TX queues (but all queues can be used for both +RX and TX, the NIC will just not sent any packet on "pure" TX queues. +Confused? So I am.). For example if you set `combined 2` you will effectively +have to create 4 rx queues in AF_XDP if you want to be sure to receive all +packets. + ## Requirements +This drivers supports Linux kernel 5.4 and later. Kernels older than 5.4 are +missing unaligned buffers support. + The Linux kernel interface must be up and have enough queues before creating the VPP AF_XDP interface, otherwise Linux will deny creating the AF_XDP socket. |