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

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Date:   Tue, 3 Aug 2021 15:04:26 -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 2:51 PM Jakub Kicinski <kuba@...nel.org> wrote:
>
> On Tue, 3 Aug 2021 14:32:19 -0700 Cong Wang wrote:
> > 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:
> > > > 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.
>
> From my own experience companies which are serious about their
> engineering have a lot of code dedicated to testing. I don't think
> we can deal with all such code upstream.
>
> At the same time I want to incentivize upstreaming all of the tests
> which are widely applicable (i.e. not HW-specific).

So, nothing special for netdevsim? This seems applicable to all code,
not just netdevsim code.

>
> Last but not least test harnesses are really weird from functional, code
> lifetime and refactoring perspective. netdevsim is not expected to keep
> uAPI as long as in-tree tests do no break/are updated as well.

Sure. Our test is not any special, sch_mq is in upstream, only sch_mq
tests are not yet. Peilin will send out sch_mq tests very soon.

>
> > > > 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.
>
> Fair, I'll send a patch.

Great! Really appreciate it.

>
> > > > 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.
> > ;)
>
> I hope the first part of this response scheds some light.
>
> > > > 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??
>
> I'd love to remove all test harnesses upstream which are not used by
> upstream tests, sure :)

Many net/*/ code can be gone. Maybe start with net/netrom/? ;)

Thanks.