* Re: linux manual question consultation
[not found] <tencent_4802CC87FBE6F4234103D9D5FD8A4811BB0A@qq.com>
@ 2022-07-05 22:45 ` Vinicius Costa Gomes
0 siblings, 0 replies; only message in thread
From: Vinicius Costa Gomes @ 2022-07-05 22:45 UTC (permalink / raw)
To: Ascend~, netdev, shemminger
Hi,
"Ascend~" <1176303504@qq.com> writes:
> Hello, I am studying the linux manual, and I don't understand something, I don't know if it is written wrong, can you provide a little help? Questions are as follows:
> URL:https://www.mankier.com/8/tc-taprio
> I see "the txtime offload mode in taprio" gives an example like this:
>
> # tc qdisc replace dev eth0 parent root handle 100 taprio \ num_tc 3 \ map 2 2 1 0 2 2 2 2 2 2 2 2 2 2 2 2 \ queues 1@0 1@0 1@0 \ base-time 1528743495910289987 \ sched-entry S 01 300000 \ sched-entry S 02 300000 \ sched-entry S 04 400000 \ flags 0x1 \ txtime-delay 200000 \ clockid CLOCK_TAI # tc qdisc replace dev $IFACE parent 100:1 etf skip_skb_check \ offload delta 200000 clockid CLOCK_TAI
>
> Why is count@offset written as queues 1@0 1@0 1@0 here?
A bit of background, txtime assisted mode is an implementation of the
enhancements for scheduled traffic state machines from IEEE 802.1Q-2018
using the "LaunchTime" (be able to specify a "precise" transmission time
of a packet) feature, using the ETF qdisc.
The current implementation has a limitation in the sense that it is only
able to use a single HW transmission queue, that's why, all traffic is
directed to a single HW queue.
> Is it mapping all traffic traffic types to queue 0?
Yes.
> If it is understood, is it meaningless to set "sched-entry"? If it is
> not understood this way, can you help me explain it? Thank you very
> much!
It's not meaningless, the traffic scheduling is done in terms of
"traffic classes" (the bit mask in 'sched-entry' are in reference to
traffic classes), "only" when sending packets down to the driver/NIC
that we use a single queue.
Note that this limitation is not a "hard" one, it most probably can be
solved with some time and better data structures in the taprio side.
Hope this answers your questions.
Cheers,
--
Vinicius
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