netdev - Re: [PATCH net-next 1/3] net: sched: update default qdisc visibility after Tx queue cnt changes

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Date:   Sun, 19 Sep 2021 16:38:30 -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>,
        Jamal Hadi Salim <jhs@...atatu.com>,
        Jiri Pirko <jiri@...nulli.us>,
        Eric Dumazet <edumazet@...gle.com>,
        Matthew Massey <matthewmassey@...com>,
        Dave Taht <dave.taht@...il.com>
Subject: Re: [PATCH net-next 1/3] net: sched: update default qdisc visibility
 after Tx queue cnt changes

On Fri, Sep 17, 2021 at 6:09 AM Jakub Kicinski <kuba@...nel.org> wrote:
>
> On Thu, 16 Sep 2021 22:46:42 -0700 Cong Wang wrote:
> > On Wed, Sep 15, 2021 at 12:36 PM Jakub Kicinski <kuba@...nel.org> wrote:
> > > On Wed, 15 Sep 2021 09:31:08 -0700 Cong Wang wrote:
> > > > Don't we need to flip the device with dev_deactivate()+dev_activate()?
> > > > It looks like the only thing this function resets is qdisc itself, and only
> > > > partially.
> > >
> > > We're only making the qdiscs visible, there should be
> > > no datapath-visible change.
> >
> > Isn't every qdisc under mq visible to datapath?
> >
> > Packets can be pending in qdisc's, and qdisc's can be scheduled
> > in TX softirq, so essentially we need to flip the device like other
>
> By visible I mean tc qdisc dump shows them. I'm adding/removing
> the qdiscs to netdev->qdisc_hash. That's only used by control
> paths to dump or find qdiscs by handle.

Oh, I see, I missed this difference. If datapath can't see this change
immediately, we don't need to flip it.

Thanks.