From: Stephen Hemminger <stephen@networkplumber.org>
To: Fengkai Sun <qcloud1014@gmail.com>
Cc: users@dpdk.org
Subject: Re: Scheduling of multiple RX/TX queues on a single port
Date: Tue, 30 May 2023 09:24:29 -0700 [thread overview]
Message-ID: <20230530092429.00e68897@hermes.local> (raw)
In-Reply-To: <CAF6YOcMuqncMm_XQfhgUc2B2jhnObmSgQrFJGQbWYLe1FGpU+Q@mail.gmail.com>
On Mon, 29 May 2023 23:02:45 +0800
Fengkai Sun <qcloud1014@gmail.com> wrote:
> Hi list,
>
> I'm curious how DPDK programs the NIC to receive/transmit packets when
> there are multiple queues on a single port.
>
> As for RX, the answer might be clear.
> The NIC can only receive a packet once at a time, since the cable only
> outputs one signal (0 or 1) at a time (correct me if I'm wrong).
> Therefore the NIC can receive a packet, check it's information, and finally
> put in into the right queue via some policies, e.g. RSS, all sequentially.
>
> However, it confuses me when it comes to TX.
> As there are multiple TX queues on the same port, the NIC must decide which
> queue to get packets from when it's idle.
> This is where scheduling lies. How does the NIC select the queue?
> Round-Robin? Does it have to enforce fairness among the queues?
>
> I'm wondering where I can find some documentation on this issue. Thank you!
Transmit scheduling is up to the hardware (not DPDK).
Generally I assume it is round-robin
but there maybe cases like priority queues (like DCB) or large packets
with segment offload.
next prev parent reply other threads:[~2023-05-30 16:24 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-05-29 15:02 Fengkai Sun
2023-05-30 16:24 ` Stephen Hemminger [this message]
2023-06-02 10:14 ` Fengkai Sun
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=20230530092429.00e68897@hermes.local \
--to=stephen@networkplumber.org \
--cc=qcloud1014@gmail.com \
--cc=users@dpdk.org \
/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.
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 NNTP newsgroup(s).