netdev - Re: iproute2: tc deletion freezes whole server

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Message-ID: <CANxWus8P8KdcZE8L1-ZLOWLxyp4OOWNY82Xw+S2qAomanViWQA@mail.gmail.com>
Date:   Tue, 31 Mar 2020 14:46:01 +0200
From:   Václav Zindulka <vaclav.zindulka@...pnet.cz>
To:     Cong Wang <xiyou.wangcong@...il.com>
Cc:     Linux Kernel Network Developers <netdev@...r.kernel.org>
Subject: Re: iproute2: tc deletion freezes whole server

On Tue, Mar 31, 2020 at 8:00 AM Cong Wang <xiyou.wangcong@...il.com> wrote:
>
> On Sat, Mar 28, 2020 at 6:04 AM Václav Zindulka
> <vaclav.zindulka@...pnet.cz> wrote:
> >
> > On Fri, Mar 27, 2020 at 11:35 AM Václav Zindulka
> > <vaclav.zindulka@...pnet.cz> wrote:
> > >
> > > Your assumption is not totally wrong. I have added some printks into
> > > fq_codel_reset() function. Final passes during deletion are processed
> > > in the if condition you added in the patch - 13706. Yet the rest and
> > > most of them go through regular routine - 1768074. 1024 is value of i
> > > in for loop.
> >
> > Ok, so I went through the kernel source a little bit. I've found out
> > that dev_deactivate is called only for interfaces that are up. My bad
> > I forgot that after deactivation of my daemon ifb interfaces are set
> > to down. Nevertheless after setting it up and doing perf record on
> > ifb0 numbers are much lower anyway. 13706 exits through your condition
> > added in patch. 41118 regular exits. I've uploaded perf report here
> > https://github.com/zvalcav/tc-kernel/tree/master/20200328
> >
> > I've also tried this on metallic interface on different server which
> > has a link on it. There were 39651 patch exits. And 286412 regular
> > exits. It is more than ifb interface, yet it is way less than sfp+
> > interface and behaves correctly.
>
> Interesting, at the point of dev_deactivate() is called, the refcnt
> should not be zero, it should be at least 1, so my patch should
> not affect dev_deactivate(), it does affect the last qdisc_put()
> after it.
>
> Of course, my intention is indeed to eliminate all of the
> unnecessary memset() in the ->reset() before ->destroy().
> I will provide you a complete patch tomorrow if you can test
> it, which should improve hfsc_reset() too.
>
> Thanks.

Sure, I'll test it and I'm looking forward to it. :-)

Thank you for all your help and effort. I appreciate it a lot.