netdev - Re: [net-next v5 2/2] net: sched: support hash/classid/cpuid selecting tx queue

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Message-ID: <CAM_iQpULb_+whVGsEv+BD09MBOdvpT-3C8WmiuBSSCbT9Yrw3Q@mail.gmail.com>
Date:   Fri, 24 Dec 2021 11:26:31 -0800
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     Tonghao Zhang <xiangxia.m.yue@...il.com>
Cc:     Linux Kernel Network Developers <netdev@...r.kernel.org>,
        Jamal Hadi Salim <jhs@...atatu.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 v5 2/2] net: sched: support hash/classid/cpuid
 selecting tx queue

On Tue, Dec 21, 2021 at 5:24 PM Tonghao Zhang <xiangxia.m.yue@...il.com> wrote:
>
> On Tue, Dec 21, 2021 at 1:57 AM Cong Wang <xiyou.wangcong@...il.com> wrote:
> >
> > On Mon, Dec 20, 2021 at 4:39 AM <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
> >
> > Once again, you are enforcing policies in kernel, which is not good.
> > Kernel should just set whatever you give to it, not selecting policies
> > like a menu.
> I agree that, but for tc/net-sched layer, there are a lot of

If you agree, why still move on with this patch? Apparently
you don't. ;)

> networking policies, for example , cls_A, act_B, sch_C.

You are justifying your logic by shifting the topics here.

The qdisc algorithm is very different from your case, it is essentially
hard, if not impossible, to completely move to user-space. Even if we
had eBPF based Qdisc, its programmablility is still very limited.
Your code is much much much easier, which is essentially one-line,
hence you have to reason to compare it with this, nor you can even
justify it.

> > Any reason why you can't obtain these values in user-space?
> Did you mean that we add this flags to iproute2 tools? This patch for
> iproute2, is not post. If the kerenl patches are accepted, I will send
> them.

Nope, I mean you can for example, obtain the CPU ID in user-space
and pass it directly to _current_ act_skbedit as it is.

Thanks.