On Fri, Oct 16, 2026 at 10:33 PM Ammar Yasser wrote:

This work is based on the original v2 RFC by Eugenio Perez:

Link: https://archives.passt.top/passt-dev/20250709174748.3514693-1-eperezma@redha...

It is the first finished patch series for vhost-kernel support after a third RFC was submitted:

Link: https://archives.passt.top/passt-dev/20260802132155.870796-1-aerosound161@gm...

vhost-net is a kernel device that allows reading and writing packets to a tap device using virtqueues instead of read(2), write(2), and their vectored counterparts. Frames are handed over through a shared descriptor ring, so several of them can be passed to the kernel at once rather than issuing a syscall per frame.

The v3 RFC didn't yield any performance improvements because, to retain correctness, sends between pasta and the vhost-kernel thread had to be synchronous. This patch series fixes this problem through the changes introduced in the last commit, titled:

"tap/tcp: Replace tcp_payload_used with a ring buffer style index"

The changes reliably yield a roughly 2x speedup on the TX path (container to host).

Numbers were obtained through iperf3 with the following methodology and results:

Pasta command: ./pasta -f --runas 0:0 --map-guest-addr 192.168.0.5 --vhost-kernel on --config-net 2729785

Host: iperf3 -s1J

Container: iperf3 -c 192.168.0.5 -t 10 -P4 -l 1M -w 32M -i1

With --vhost-kernel on:

[SUM] 0.00-10.00 sec 1.36 GBytes 1.17 Gbits/sec 3643 sender [SUM] 0.00-10.00 sec 1.16 GBytes 999 Mbits/sec receiver

With --vhost-kernel off:

[SUM] 0.00-10.00 sec 700 MBytes 587 Mbits/sec 3556 sender [SUM] 0.00-10.10 sec 495 MBytes 411 Mbits/sec receiver

Sounds good :). Sorry I didn't have the time to review the series properly, but I suspect you can use VIRTIO F IN ORDER to both: * Increase the performance even more. * Make the code simpler as pasta fits (or it used to fit) very nicely with it. It would have make *my* code simpler at least, so I'm suspecting it will make this series simpler too. Does that help? Thanks!

v2: - removed all use of epoll_ctl in vhost_setup_eventfds in favor of epoll_add - prevent all functions that register memory regions into the vhost_memory object from overflowing - remove the unions with flexible array members in vring_avail_pasta and vring_used_pasta in favor of hardcoding the ring array to have VHOST_NDESCS entries to avoid having to ignore Wpedantic - remove the && operator with TCP_CURR_IDX when computing no_csum - make desc_id in tx_reap a uint32_t - don't make vhost-kernel a required argument

Ammar Yasser (7): tap: Move the tap_hdr file to a separate file conf: Add context fields, epoll types and --vhost-kernel flag to pasta virtio: Add the pasta vhost-net interface and implementation tap: Implement the pasta vhost-net from-guest path tap, tcp, udp: Prepare the to-guest path for vhost-net tap: Implement the pasta vhost-net to-guest path tap/tcp: Replace tcp_payload_used with a ring buffer style index

Makefile | 2 +- conf.c | 19 +++ epoll_type.h | 4 + passt.c | 9 ++ passt.h | 79 ++++++++++- tap.c | 368 +++++++++++++++++++++++++++++++++++++++++++++------ tap.h | 47 ++----- tap_hdr.h | 23 ++++ tcp_buf.c | 149 ++++++++++++++++----- tcp_buf.h | 4 + udp.c | 47 +++++-- udp.h | 3 + util.c | 18 +++ util.h | 2 + vhost.c | 295 +++++++++++++++++++++++++++++++++++++++++ vhost.h | 91 +++++++++++++ 16 files changed, 1036 insertions(+), 124 deletions(-) create mode 100644 tap_hdr.h create mode 100644 vhost.c create mode 100644 vhost.h

-- 2.39.5 (Apple Git-154)