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

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Date:   Tue, 15 Feb 2022 09:40:03 +0800
From:   Tonghao Zhang <xiangxia.m.yue@...il.com>
To:     Jamal Hadi Salim <jhs@...atatu.com>
Cc:     Linux Kernel Network Developers <netdev@...r.kernel.org>,
        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 Tue, Feb 15, 2022 at 8:22 AM Jamal Hadi Salim <jhs@...atatu.com> wrote:
>
> 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.
Hi
I try to explain. there are two tx-queue range, e.g. A(Q0-Qn), B(Qn+1-Qm).
A is used for latency sensitive traffic. B is used for bulk sensitive
traffic. A may be shared by Pods/Containers which key is
high throughput. B may be shared by Pods/Containers which key is low
latency. So we can do the balance in range A for latency sensitive
traffic.
So we can use the skb->hash or CPUID or classid to classify the
packets in range A or B. The balance policies are used for different
use case.
For skb->hash, the packets from Pods/Containers will share the range.
Should to know that one Pod/Container may use the multi TCP/UDP flows.
That flows share the tx queue range.
For CPUID, while Pod/Container use the multi flows, pod pinned on one
CPU will use one tx-queue in range A or B.
For CLASSID, the Pod may contain the multi containters.

skb->priority may be used by applications. we can't require
application developer to change them.


>
> cheers,
> jamal
>
>


-- 
Best regards, Tonghao