From: Stefano Brivio <sbrivio@redhat.com>
To: Laurent Vivier <lvivier@redhat.com>
Cc: passt-dev@passt.top
Subject: Re: [PATCH v8 7/8] vhost-user: add vhost-user
Date: Thu, 14 Nov 2024 15:23:16 +0100 [thread overview]
Message-ID: <20241114152316.6843a427@elisabeth> (raw)
In-Reply-To: <81955149-fc8f-47ef-b6fb-ce284e8e8b1b@redhat.com>
On Thu, 14 Nov 2024 11:23:11 +0100
Laurent Vivier <lvivier@redhat.com> wrote:
> On 17/10/2024 02:10, Stefano Brivio wrote:
> >> +/**
> >> + * tcp_vu_data_from_sock() - Handle new data from socket, queue to vhost-user,
> >> + * in window
> >> + * @c: Execution context
> >> + * @conn: Connection pointer
> >> + *
> >> + * Return: Negative on connection reset, 0 otherwise
> >> + */
> >> +int tcp_vu_data_from_sock(const struct ctx *c, struct tcp_tap_conn *conn)
> >> +{
> >> + uint32_t wnd_scaled = conn->wnd_from_tap << conn->ws_from_tap;
> >> + struct vu_dev *vdev = c->vdev;
> >> + struct vu_virtq *vq = &vdev->vq[VHOST_USER_RX_QUEUE];
> >> + const struct flowside *tapside = TAPFLOW(conn);
> >> + uint16_t mss = MSS_GET(conn);
> >> + size_t l2_hdrlen, fillsize;
> >> + int i, iov_cnt, iov_used;
> >> + int v4 = CONN_V4(conn);
> >> + uint32_t already_sent = 0;
> >> + const uint16_t *check;
> >> + struct iovec *first;
> >> + int frame_size;
> >> + int num_buffers;
> >> + ssize_t len;
> >> +
> >> + if (!vu_queue_enabled(vq) || !vu_queue_started(vq)) {
> >> + flow_err(conn,
> >> + "Got packet, but RX virtqueue not usable yet");
> >> + return 0;
> >> + }
> >> +
> >> + already_sent = conn->seq_to_tap - conn->seq_ack_from_tap;
> >> +
> >> + if (SEQ_LT(already_sent, 0)) {
> >> + /* RFC 761, section 2.1. */
> >> + flow_trace(conn, "ACK sequence gap: ACK for %u, sent: %u",
> >> + conn->seq_ack_from_tap, conn->seq_to_tap);
> >> + conn->seq_to_tap = conn->seq_ack_from_tap;
> >> + already_sent = 0;
> >> + }
> >> +
> >> + if (!wnd_scaled || already_sent >= wnd_scaled) {
> >> + conn_flag(c, conn, STALLED);
> >> + conn_flag(c, conn, ACK_FROM_TAP_DUE);
> >> + return 0;
> >> + }
> >> +
> >> + /* Set up buffer descriptors we'll fill completely and partially. */
> >> +
> >> + fillsize = wnd_scaled;
> >> +
> >> + if (peek_offset_cap)
> >> + already_sent = 0;
> >> +
> >> + iov_vu[0].iov_base = tcp_buf_discard;
> >> + iov_vu[0].iov_len = already_sent;
> >> + fillsize -= already_sent;
> >> +
> >> + /* collect the buffers from vhost-user and fill them with the
> >> + * data from the socket
> >> + */
> >> + iov_cnt = tcp_vu_sock_recv(c, conn, v4, fillsize, &len);
> >> + if (iov_cnt <= 0)
> >> + return iov_cnt;
> >> +
> >> + len -= already_sent;
> >> + if (len <= 0) {
> >> + conn_flag(c, conn, STALLED);
> >> + vu_queue_rewind(vq, iov_cnt);
> >> + return 0;
> >> + }
> >> +
> >> + conn_flag(c, conn, ~STALLED);
> >> +
> >> + /* Likely, some new data was acked too. */
> >> + tcp_update_seqack_wnd(c, conn, 0, NULL);
> >> +
> >> + /* initialize headers */
> >> + l2_hdrlen = tcp_vu_l2_hdrlen(!v4);
> >> + iov_used = 0;
> >> + num_buffers = 0;
> >> + check = NULL;
> >> + frame_size = 0;
> >> +
> >> + /* iov_vu is an array of buffers and the buffer size can be
> >> + * smaller than the frame size we want to use but with
> >> + * num_buffer we can merge several virtio iov buffers in one packet
> >> + * we need only to set the packet headers in the first iov and
> >> + * num_buffer to the number of iov entries
> > ...this part is clear to me, what I don't understand is if we still
> > have a way to guarantee that the sum of several buffers is big enough
> > to fit frame_size bytes.
>
> We don't have this garantee. But I think it's the same for the socket version?
Well, there we do:
fill_bufs = DIV_ROUND_UP(wnd_scaled - already_sent, mss);
if (fill_bufs > TCP_FRAMES) {
fill_bufs = TCP_FRAMES;
and we don't fetch more data than that from the socket (in one pass).
Is this implicit in the i < iov_cnt loop condition here? That's the part
I don't understand: how do we limit the amount of data we can dequeue
from a socket in one single pass.
--
Stefano
next prev parent reply other threads:[~2024-11-14 14:23 UTC|newest]
Thread overview: 50+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-10-10 12:28 [PATCH v8 0/8] Add vhost-user support to passt. (part 3) Laurent Vivier
2024-10-10 12:28 ` [PATCH v8 1/8] packet: replace struct desc by struct iovec Laurent Vivier
2024-10-10 12:28 ` [PATCH v8 2/8] vhost-user: introduce virtio API Laurent Vivier
2024-10-10 12:28 ` [PATCH v8 3/8] vhost-user: introduce vhost-user API Laurent Vivier
2024-10-10 12:28 ` [PATCH v8 4/8] udp: Prepare udp.c to be shared with vhost-user Laurent Vivier
2024-10-14 4:29 ` David Gibson
2024-10-10 12:28 ` [PATCH v8 5/8] tcp: Export headers functions Laurent Vivier
2024-10-14 4:29 ` David Gibson
2024-10-10 12:29 ` [PATCH v8 6/8] passt: rename tap_sock_init() to tap_backend_init() Laurent Vivier
2024-10-14 4:30 ` David Gibson
2024-10-14 22:38 ` Stefano Brivio
2024-10-10 12:29 ` [PATCH v8 7/8] vhost-user: add vhost-user Laurent Vivier
2024-10-15 3:23 ` David Gibson
2024-10-16 10:07 ` Laurent Vivier
2024-10-16 16:26 ` Stefano Brivio
2024-10-15 19:54 ` Stefano Brivio
2024-10-16 0:41 ` David Gibson
2024-10-17 0:10 ` Stefano Brivio
2024-10-17 11:25 ` Stefano Brivio
2024-10-17 11:54 ` Laurent Vivier
2024-10-17 17:18 ` Laurent Vivier
2024-10-17 17:25 ` Laurent Vivier
2024-10-17 17:33 ` Stefano Brivio
2024-10-17 21:21 ` Stefano Brivio
2024-10-22 12:59 ` Laurent Vivier
2024-10-22 13:19 ` Stefano Brivio
2024-10-22 18:19 ` Stefano Brivio
2024-10-22 18:22 ` Stefano Brivio
2024-10-23 15:27 ` Laurent Vivier
2024-10-23 16:23 ` Stefano Brivio
2024-10-17 0:10 ` Stefano Brivio
2024-10-17 7:28 ` Laurent Vivier
2024-10-17 8:33 ` Stefano Brivio
2024-11-14 10:20 ` Laurent Vivier
2024-11-14 14:23 ` Stefano Brivio
2024-11-14 15:16 ` Laurent Vivier
2024-11-14 15:38 ` Stefano Brivio
2024-11-14 10:23 ` Laurent Vivier
2024-11-14 14:23 ` Stefano Brivio [this message]
2024-11-15 8:30 ` Laurent Vivier
2024-11-15 10:08 ` Stefano Brivio
2024-11-14 10:29 ` Laurent Vivier
2024-11-14 14:23 ` Stefano Brivio
2024-11-15 11:13 ` Laurent Vivier
2024-11-15 11:23 ` Stefano Brivio
2024-10-10 12:29 ` [PATCH v8 8/8] test: Add tests for passt in vhost-user mode Laurent Vivier
2024-10-15 3:40 ` David Gibson
2024-10-15 19:54 ` Stefano Brivio
2024-10-16 8:06 ` Laurent Vivier
2024-10-16 9:47 ` Stefano Brivio
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20241114152316.6843a427@elisabeth \
--to=sbrivio@redhat.com \
--cc=lvivier@redhat.com \
--cc=passt-dev@passt.top \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
Code repositories for project(s) associated with this public inbox
https://passt.top/passt
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for IMAP folder(s).