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Date: Mon, 20 Feb 2023 16:15:43 +0100
From: Ferenc Fejes <fejes@....elte.hu>
To: Péter Antal <peti.antal99@...il.com>,
netdev@...r.kernel.org
Cc: John Fastabend <john.fastabend@...il.com>,
Vladimir Oltean <vladimir.oltean@....com>,
Stephen Hemminger <stephen@...workplumber.org>,
Vinicius Costa Gomes <vinicius.gomes@...el.com>,
Péter Antal <antal.peti99@...il.com>
Subject: Re: [PATCH iproute2] man: tc-mqprio: extend prio-tc-queue mapping
with examples
Hi!
On Mon, 2023-02-20 at 16:05 +0100, Péter Antal wrote:
> The current mqprio manual is not detailed about queue mapping
> and priorities, this patch adds some examples to it.
Thank you Péter for doing this! The same principles however applies to
tc-taprio as well so it would be nice to see a v2 with those included
too.
>
> Suggested-by: Ferenc Fejes <fejes@....elte.hu>
> Signed-off-by: Péter Antal <peti.antal99@...il.com>
> ---
> man/man8/tc-mqprio.8 | 96
> ++++++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 96 insertions(+)
>
> diff --git a/man/man8/tc-mqprio.8 b/man/man8/tc-mqprio.8
> index 4b9e942e..16ecb9a1 100644
> --- a/man/man8/tc-mqprio.8
> +++ b/man/man8/tc-mqprio.8
> @@ -98,6 +98,7 @@ belong to an application. See kernel and cgroup
> documentation for details.
> .TP
> num_tc
> Number of traffic classes to use. Up to 16 classes supported.
> +You cannot have more classes than queues
>
> .TP
> map
> @@ -119,6 +120,8 @@ Set to
> to support hardware offload. Set to
> .B 0
> to configure user specified values in software only.
> +The default value of this parameter is
> +.B 1
It especially important when applied to multi TX queue veth.
Vladimir already addressed this in kernel UAPI to give more expressive
error message:
https://lore.kernel.org/netdev/20230220122343.1156614-6-vladimir.oltean@nxp.com/T/#u
But knowing the default parameter from the manpage is still a good
addition IMO.
>
> .TP
> mode
> @@ -146,5 +149,98 @@ max_rate
> Maximum value of bandwidth rate limit for a traffic class.
>
>
> +.SH EXAMPLE
> +
> +The following example shows how to attach priorities to 4 traffic
> classes ("num_tc 4"),
> +and then how to pair these traffic classes with 4 hardware queues
> with mqprio,
> +with hardware coordination ("hw 1", or does not specified, because 1
> is the default value).
> +Traffic class 0 (tc0) is mapped to hardware queue 0 (q0), tc1 is
> mapped to q1,
> +tc2 is mapped to q2, and tc3 is mapped q3.
> +
> +.EX
> +# tc qdisc add dev eth0 root mqprio \
> + num_tc 4 \
> + map 0 0 0 0 1 1 1 1 2 2 2 2 3 3 3 3 \
> + queues 1@0 1@1 1@2 1@3 \
> + hw 1
> +.EE
> +
> +The next example shows how to attach priorities to 3 traffic classes
> ("num_tc 3"),
> +and how to pair these traffic classes with 4 queues,
> +without hardware coordination ("hw 0").
> +Traffic class 0 (tc0) is mapped to hardware queue 0 (q0), tc1 is
> mapped to q1,
> +tc2 and is mapped to q2 and q3, where the queue selection between
> these
> +two queues is somewhat randomly decided.
> +
> +.EX
> +# tc qdisc add dev eth0 root mqprio \
> + num_tc 3 \
> + map 0 0 0 0 1 1 1 1 2 2 2 2 2 2 2 2 \
> + queues 1@0 1@1 2@2 \
> + hw 0
> +.EE
> +
> +
> +In both cases from above the priority values from 0 to 3 (prio0-3)
> are
> +mapped to tc0, prio4-7 are mapped to tc1, and the
> +prio8-11 are mapped to tc2 ("map" attribute). The last four priority
> values
> +(prio12-15) are mapped in different ways in the two examples.
> +They are mapped to tc3 in the first example and mapped to tc2 in the
> second example.
> +The values of these two examples are the following:
> +
> + ┌────┬────┬───────┐ ┌────┬────┬────────┐
> + │Prio│ tc │ queue │ │Prio│ tc │ queue │
> + ├────┼────┼───────┤ ├────┼────┼────────┤
> + │ 0 │ 0 │ 0 │ │ 0 │ 0 │ 0 │
> + │ 1 │ 0 │ 0 │ │ 1 │ 0 │ 0 │
> + │ 2 │ 0 │ 0 │ │ 2 │ 0 │ 0 │
> + │ 3 │ 0 │ 0 │ │ 3 │ 0 │ 0 │
> + │ 4 │ 1 │ 1 │ │ 4 │ 1 │ 1 │
> + │ 5 │ 1 │ 1 │ │ 5 │ 1 │ 1 │
> + │ 6 │ 1 │ 1 │ │ 6 │ 1 │ 1 │
> + │ 7 │ 1 │ 1 │ │ 7 │ 1 │ 1 │
> + │ 8 │ 2 │ 2 │ │ 8 │ 2 │ 2 or 3 │
> + │ 9 │ 2 │ 2 │ │ 9 │ 2 │ 2 or 3 │
> + │ 10 │ 2 │ 2 │ │ 10 │ 2 │ 2 or 3 │
> + │ 11 │ 2 │ 2 │ │ 11 │ 2 │ 2 or 3 │
> + │ 12 │ 3 │ 3 │ │ 12 │ 2 │ 2 or 3 │
> + │ 13 │ 3 │ 3 │ │ 13 │ 2 │ 2 or 3 │
> + │ 14 │ 3 │ 3 │ │ 14 │ 2 │ 2 or 3 │
> + │ 15 │ 3 │ 3 │ │ 15 │ 2 │ 2 or 3 │
> + └────┴────┴───────┘ └────┴────┴────────┘
> + example1 example2
> +
> +
> +Another example of queue mapping is the following.
> +There are 5 traffic classes, and there are 8 hardware queues.
> +
> +.EX
> +# tc qdisc add dev eth0 root mqprio \
> + num_tc 5 \
> + map 0 0 0 1 1 1 1 2 2 3 3 4 4 4 4 4 \
> + queues 1@0 2@1 1@3 1@4 3@5
> +.EE
> +
> +The value mapping is the following for this example:
> +
> + ┌───────┐
> + tc0────┤Queue 0│◄────1@0
> + ├───────┤
> + ┌─┤Queue 1│◄────2@1
> + tc1──┤ ├───────┤
> + └─┤Queue 2│
> + ├───────┤
> + tc2────┤Queue 3│◄────1@3
> + ├───────┤
> + tc3────┤Queue 4│◄────1@4
> + ├───────┤
> + ┌─┤Queue 5│◄────3@5
> + │ ├───────┤
> + tc4──┼─┤Queue 6│
> + │ ├───────┤
> + └─┤Queue 7│
> + └───────┘
> +
> +
> .SH AUTHORS
> John Fastabend, <john.r.fastabend@...el.com>
Best,
Ferenc
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