On 2020/11/19 下午7:13, Andrew Melnychenko wrote:
> From: Andrew <andrew@daynix.com>
>
> Also, added maintainers information.
>
> Signed-off-by: Yuri Benditovich <yuri.benditovich@daynix.com>
> Signed-off-by: Andrew Melnychenko <andrew@daynix.com>
> ---
> MAINTAINERS | 7 +++
> docs/ebpf_rss.rst | 133 ++++++++++++++++++++++++++++++++++++++++++++++
> 2 files changed, 140 insertions(+)
> create mode 100644 docs/ebpf_rss.rst
>
> diff --git a/MAINTAINERS b/MAINTAINERS
> index 2c22bbca5a..d93c85b867 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -3111,6 +3111,13 @@ S: Maintained
> F: hw/semihosting/
> F: include/hw/semihosting/
>
> +EBPF:
> +M: Jason Wang <jasowang@redhat.com>
> +R: Andrew Melnychenko <andrew@daynix.com>
> +R: Yuri Benditovich <yuri.benditovich@daynix.com>
> +S: Maintained
> +F: ebpf/*
> +
> Build and test automation
> -------------------------
> Build and test automation
> diff --git a/docs/ebpf_rss.rst b/docs/ebpf_rss.rst
> new file mode 100644
> index 0000000000..f832defdf4
> --- /dev/null
> +++ b/docs/ebpf_rss.rst
> @@ -0,0 +1,133 @@
> +===========================
> +eBPF RSS virtio-net support
> +===========================
> +
> +RSS(Receive Side Scaling) is used to distribute network packets to guest virtqueues
> +by calculating packet hash. Usually every queue is processed then by a specific guest CPU core.
> +
> +For now there are 2 RSS implementations in qemu:
> +- 'in-qemu' RSS (functions if qemu receives network packets, i.e. vhost=off)
> +- eBPF RSS (can function with also with vhost=on)
> +
> +eBPF support (CONFIG_EBPF) is enabled by 'configure' script.
> +To enable eBPF RSS support use './configure --enable-bpf'.
> +
> +If steering BPF is not set for kernel's TUN module, the TUN uses automatic selection
> +of rx virtqueue based on lookup table built according to calculated symmetric hash
> +of transmitted packets.
> +If steering BPF is set for TUN the BPF code calculates the hash of packet header and
> +returns the virtqueue number to place the packet to.
> +
> +Simplified decision formula:
> +
> +.. code:: C
> +
> + queue_index = indirection_table[hash(<packet data>)%<indirection_table size>]
> +
> +
> +Not for all packets, the hash can/should be calculated.
> +
> +Note: currently, eBPF RSS does not support hash reporting.
> +
> +eBPF RSS turned on by different combinations of vhost-net, vitrio-net and tap configurations:
> +
> +- eBPF is used:
> +
> + tap,vhost=off & virtio-net-pci,rss=on,hash=off
> +
> +- eBPF is used:
> +
> + tap,vhost=on & virtio-net-pci,rss=on,hash=off
> +
> +- 'in-qemu' RSS is used:
> +
> + tap,vhost=off & virtio-net-pci,rss=on,hash=on
> +
> +- eBPF is used, hash population feature is not reported to the guest:
> +
> + tap,vhost=on & virtio-net-pci,rss=on,hash=on
> +
> +If CONFIG_EBPF is not set then only 'in-qemu' RSS is supported.
> +Also 'in-qemu' RSS, as a fallback, is used if the eBPF program failed to load or set to TUN.
> +
> +RSS eBPF program
> +----------------
> +
> +RSS program located in ebpf/tun_rss_steering.h as an array of 'struct bpf_insn'.
> +So the program is part of the qemu binary.
> +Initially, the eBPF program was compiled by clang and source code located at ebpf/rss.bpf.c.
> +Prerequisites to recompile the eBPF program (regenerate ebpf/tun_rss_steering.h):
> +
> + llvm, clang, kernel source tree, python3 + (pip3 pyelftools)
> + Adjust 'linuxhdrs' in Makefile.ebpf to reflect the location of the kernel source tree
> +
> + $ cd ebpf
> + $ make -f Makefile.ebpf
> +
> +Note the python script for convertation from eBPF ELF object to '.h' file - Ebpf_to_C.py:
> +
> + $ python EbpfElf_to_C.py rss.bpf.o tun_rss_steering
> +
> +The first argument of the script is ELF object, second - section name where the eBPF program located.
> +The script would generate <section name>.h file with eBPF instructions and 'relocate array'.
> +'relocate array' is an array of 'struct fixup_mapfd_t' with the name of the eBPF map and instruction offset where the file descriptor of the map should be placed.
> +
> +Current eBPF RSS implementation uses 'bounded loops' with 'backward jump instructions' which present in the last kernels.
> +Overall eBPF RSS works on kernels 5.8+.
This reminds me that we probably need to probe this ability via
configure script.
I'm not sure. One can boot with an older kernel, build qemu and run it with a newer kernel, correct?
Thanks
> +
> +eBPF RSS implementation
> +-----------------------
> +
> +eBPF RSS loading functionality located in ebpf/ebpf_rss.c and ebpf/ebpf_rss.h.
> +
> +The `struct EBPFRSSContext` structure that holds 4 file descriptors:
> +
> +- ctx - pointer of the libbpf context.
> +- program_fd - file descriptor of the eBPF RSS program.
> +- map_configuration - file descriptor of the 'configuration' map. This map contains one element of 'struct EBPFRSSConfig'. This configuration determines eBPF program behavior.
> +- map_toeplitz_key - file descriptor of the 'Toeplitz key' map. One element of the 40byte key prepared for the hashing algorithm.
> +- map_indirections_table - 128 elements of queue indexes.
> +
> +`struct EBPFRSSConfig` fields:
> +
> +- redirect - "boolean" value, should the hash be calculated, on false - `default_queue` would be used as the final decision.
> +- populate_hash - for now, not used. eBPF RSS doesn't support hash reporting.
> +- hash_types - binary mask of different hash types. See `VIRTIO_NET_RSS_HASH_TYPE_*` defines. If for packet hash should not be calculated - `default_queue` would be used.
> +- indirections_len - length of the indirections table, maximum 128.
> +- default_queue - the queue index that used for packet that shouldn't be hashed. For some packets, the hash can't be calculated(g.e ARP).
> +
> +Functions:
> +
> +- `ebpf_rss_init()` - sets ctx to NULL, which indicates that EBPFRSSContext is not loaded.
> +- `ebpf_rss_load()` - creates 3 maps and loads eBPF program from tun_rss_steering.h. Returns 'true' on success. After that, program_fd can be used to set steering for TAP.
> +- `ebpf_rss_set_all()` - sets values for eBPF maps. `indirections_table` length is in EBPFRSSConfig. `toeplitz_key` is VIRTIO_NET_RSS_MAX_KEY_SIZE aka 40 bytes array.
> +- `ebpf_rss_unload()` - close all file descriptors and set ctx to NULL.
> +
> +Simplified eBPF RSS workflow:
> +
> +.. code:: C
> +
> + struct EBPFRSSConfig config;
> + config.redirect = 1;
> + config.hash_types = VIRTIO_NET_RSS_HASH_TYPE_UDPv4 | VIRTIO_NET_RSS_HASH_TYPE_TCPv4;
> + config.indirections_len = VIRTIO_NET_RSS_MAX_TABLE_LEN;
> + config.default_queue = 0;
> +
> + uint16_t table[VIRTIO_NET_RSS_MAX_TABLE_LEN] = {...};
> + uint8_t key[VIRTIO_NET_RSS_MAX_KEY_SIZE] = {...};
> +
> + struct EBPFRSSContext ctx;
> + ebpf_rss_init(&ctx);
> + ebpf_rss_load(&ctx);
> + ebpf_rss_set_all(&ctx, &config, table, key);
> + if (net_client->info->set_steering_ebpf != NULL) {
> + net_client->info->set_steering_ebpf(net_client, ctx->program_fd);
> + }
> + ...
> + ebpf_unload(&ctx);
> +
> +
> +NetClientState SetSteeringEBPF()
> +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> +
> +For now, `set_steering_ebpf()` method supported by Linux TAP NetClientState. The method requires an eBPF program file descriptor as an argument.