netdev - Re: [net-next v8 2/2] net: sched: support hash/classid/cpuid selecting tx queue

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Message-ID: <0b486c4e-0af5-d142-44e5-ed81aa0b98c2@mojatatu.com>
Date:   Mon, 14 Feb 2022 19:22:42 -0500
From:   Jamal Hadi Salim <jhs@...atatu.com>
To:     xiangxia.m.yue@...il.com, netdev@...r.kernel.org
Cc:     Cong Wang <xiyou.wangcong@...il.com>,
        Jiri Pirko <jiri@...nulli.us>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        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>
Subject: Re: [net-next v8 2/2] net: sched: support hash/classid/cpuid
 selecting tx queue

On 2022-01-26 09:32, xiangxia.m.yue@...il.com wrote:
> From: Tonghao Zhang <xiangxia.m.yue@...il.com>
> 
> This patch allows user to select queue_mapping, range
> from A to B. And user can use skbhash, cgroup classid
> and cpuid to select Tx queues. Then we can load balance
> packets from A to B queue. The range is an unsigned 16bit
> value in decimal format.
> 
> $ tc filter ... action skbedit queue_mapping skbhash A B
> 
> "skbedit queue_mapping QUEUE_MAPPING" (from "man 8 tc-skbedit")
> is enhanced with flags:
> * SKBEDIT_F_TXQ_SKBHASH
> * SKBEDIT_F_TXQ_CLASSID
> * SKBEDIT_F_TXQ_CPUID
> 
> Use skb->hash, cgroup classid, or cpuid to distribute packets.
> Then same range of tx queues can be shared for different flows,
> cgroups, or CPUs in a variety of scenarios.
> 
> For example, F1 may share range R1 with F2. The best way to do
> that is to set flag to SKBEDIT_F_TXQ_HASH, using skb->hash to
> share the queues. If cgroup C1 want to share the R1 with cgroup
> C2 .. Cn, use the SKBEDIT_F_TXQ_CLASSID. Of course, in some other
> scenario, C1 use R1, while Cn can use the Rn.
> 

So while i dont agree that ebpf is the solution for reasons i mentioned
earlier - after looking at the details think iam confused by this change
and maybe i didnt fully understand the use case.

What is the driver that would work  with this?
You said earlier packets are coming out of some pods and then heading to
the wire and you are looking to balance and isolate between bulk and
latency  sensitive traffic - how are any of these metadatum useful for
that? skb->priority seems more natural for that.


cheers,
jamal