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Date:   Tue, 3 Aug 2021 14:51:24 -0700
From:   Jakub Kicinski <>
To:     Cong Wang <>
Cc:     David Miller <>,
        Linux Kernel Network Developers <>,
        "Cong Wang ." <>,
        Peilin Ye <>
Subject: Re: [PATCH net-next] Revert "netdevsim: Add multi-queue support"

On Tue, 3 Aug 2021 14:32:19 -0700 Cong Wang wrote:
> On Tue, Aug 3, 2021 at 2:18 PM Jakub Kicinski <> wrote:
> >
> > On Tue, 3 Aug 2021 10:11:13 -0700 Cong Wang wrote:  
> > > On Tue, Aug 3, 2021 at 5:39 AM Jakub Kicinski <> 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).

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.

> > > 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.

> > > 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 :)

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