netdev - Re: [PATCH net-next] Revert "netdevsim: Add multi-queue support"

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Date:   Tue, 3 Aug 2021 14:32:19 -0700
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     Jakub Kicinski <kuba@...nel.org>
Cc:     David Miller <davem@...emloft.net>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>,
        "Cong Wang ." <cong.wang@...edance.com>,
        Peilin Ye <peilin.ye@...edance.com>
Subject: Re: [PATCH net-next] Revert "netdevsim: Add multi-queue support"

On Tue, Aug 3, 2021 at 2:18 PM Jakub Kicinski <kuba@...nel.org> wrote:
>
> On Tue, 3 Aug 2021 10:11:13 -0700 Cong Wang wrote:
> > On Tue, Aug 3, 2021 at 5:39 AM Jakub Kicinski <kuba@...nel.org> wrote:
> > >
> > > This reverts commit d4861fc6be581561d6964700110a4dede54da6a6.
> > >
> > > netdevsim is for enabling upstream tests, two weeks in
> > > and there's no sign of upstream test using the "mutli-queue"
> > > option.
> >
> > Since when netdevsim is *only* for upstream tests?
>
> Since it was created.

Why it was created only for upstream? IOW, what's wrong with
using it only for non-upstream tests?

BTW, we also use dummy device for testing, it is not only for
upstream. It is extremely odd to single netdevsim out. I don't
see any special reason here.

>
> > Even if so, where is this documented? And why not just point it
> > out when reviewing it instead of silently waiting for weeks?
>
> I was AFK for the last two weeks.

How about documenting it in netdev-FAQ (or literally any doc)?
This would save everyone's time.

>
> > > We can add this option back when such test materializes.
> > > Right now it's dead code.
> >
> > It is clearly not dead. We internally used it for testing sch_mq,
> > this is clearly stated in the git log.
>
> Please contribute those tests upstream or keep any test harness
> they require where such test are, out of tree.

Peilin will add tc-testing for sch_mq which requires this netdevsim
feature.

>
> > How did you draw such a conclusion without talking to authors?
>
> There is no upstream test using this code, and I did CC you, didn't I?

There are downstream tests, which are mentioned in changelog.

I am pretty sure upstream tests only cover part of the whole networking
code, if you really want to apply the rule, a lot of code are already dead.
Once again, I don't see any reason why you only treat netdevsim differently.
;)

>
> > But this does remind me of using netdevsim for tc-testing.
>
> Please bring the code back as part of the series adding upstream tests.

Please remove all those not covered by upstream tests just to be fair??

Thank you!