netdev - Re: [net-next v1 1/2] net: sched: use queue

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Message-ID: <20211206124001.5a264583@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com>
Date:   Mon, 6 Dec 2021 12:40:01 -0800
From:   Jakub Kicinski <kuba@...nel.org>
To:     xiangxia.m.yue@...il.com
Cc:     netdev@...r.kernel.org, Jamal Hadi Salim <jhs@...atatu.com>,
        Cong Wang <xiyou.wangcong@...il.com>,
        Jiri Pirko <jiri@...nulli.us>,
        "David S. Miller" <davem@...emloft.net>,
        Jonathan Lemon <jonathan.lemon@...il.com>,
        Eric Dumazet <edumazet@...gle.com>,
        Alexander Lobakin <alobakin@...me>,
        Paolo Abeni <pabeni@...hat.com>,
        Talal Ahmad <talalahmad@...gle.com>,
        Kevin Hao <haokexin@...il.com>,
        Ilias Apalodimas <ilias.apalodimas@...aro.org>,
        Kees Cook <keescook@...omium.org>,
        Kumar Kartikeya Dwivedi <memxor@...il.com>,
        Antoine Tenart <atenart@...nel.org>,
        Wei Wang <weiwan@...gle.com>, Arnd Bergmann <arnd@...db.de>,
        alexander.duyck@...il.com
Subject: Re: [net-next v1 1/2] net: sched: use queue_mapping to pick tx
 queue

On Mon,  6 Dec 2021 16:05:11 +0800 xiangxia.m.yue@...il.com wrote:
>   +----+      +----+      +----+
>   | P1 |      | P2 |      | Pn |
>   +----+      +----+      +----+
>     |           |           |
>     +-----------+-----------+
>                 |
>                 | clsact/skbedit
>                 |    MQ
>                 v
>     +-----------+-----------+
>     | q0        | q1        | qn
>     v           v           v
>    HTB         HTB   ...   FIFO

The usual suggestion these days is to try to use FQ + EDT to
implement efficient policies. You don't need dedicated qdiscs, 
just modulate transmission time appropriately on egress of the
container.

In general recording the decision in the skb seems a little heavy
handed. We just need to carry the information from the egress hook
to the queue selection a few lines below. Or in fact maybe egress
hook shouldn't be used for this in the first place, and we need 
a more appropriate root qdisc than simple mq?

Not sure. What I am sure of is that you need to fix these warnings:

include/linux/skbuff.h:937: warning: Function parameter or member 'tc_skip_txqueue' not described in 'sk_buff'

ERROR: spaces required around that '=' (ctx:VxW)
#103: FILE: net/sched/act_skbedit.c:42:
+	queue_mapping= (queue_mapping & 0xff) + hash % mapping_mod;
 	             ^

;)