netdev - Re: iproute2: tc deletion freezes whole server

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Message-ID: <CAM_iQpXjsrraZpU3xhTvQ=owwzSTjAVdx-Aszz-yLitFzE5GsA@mail.gmail.com>
Date:   Mon, 4 May 2020 10:46:13 -0700
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     Václav Zindulka <vaclav.zindulka@...pnet.cz>
Cc:     Linux Kernel Network Developers <netdev@...r.kernel.org>
Subject: Re: iproute2: tc deletion freezes whole server

On Thu, Apr 30, 2020 at 5:40 AM Václav Zindulka
<vaclav.zindulka@...pnet.cz> wrote:
>
> On Wed, Apr 15, 2020 at 5:01 PM Václav Zindulka
> <vaclav.zindulka@...pnet.cz> wrote:
> > > > > The problem is actually more complicated than I thought, although it
> > > > > needs more work, below is the first pile of patches I have for you to
> > > > > test:
> > > > >
> > > > > https://github.com/congwang/linux/commits/qdisc_reset
> > > > >
> > > > > It is based on the latest net-next branch. Please let me know the result.
> > > >
> > > > I have applied all the patches in your four commits to my custom 5.4.6
> > > > kernel source. There was no change in the amount of fq_codel_reset
> > > > calls. Tested on ifb, RJ45 and SFP+ interfaces.
> > >
> > > It is true my patches do not reduce the number of fq_codel_reset() calls,
> > > they are intended to reduce the CPU time spent in each fq_codel_reset().
> > >
> > > Can you measure this? Note, you do not have to add your own printk()
> > > any more, because my patches add a few tracepoints, especially for
> > > qdisc_reset(). So you can obtain the time by checking the timestamps
> > > of these trace events. Of course, you can also use perf trace like you
> > > did before.
> >
> > Sorry for delayed responses. We were moving to a new house so I didn't
> > have much time to test it. I've measured your pile of patches applied
> > vs unpatched kernel. Result is a little bit better, but it is only
> > about 1s faster. Results are here. Do you need any additional reports
> > or measurements of other interfaces?
> > https://github.com/zvalcav/tc-kernel/tree/master/20200415 I've
> > recompiled the kernel without printk which had some overhead too.
>
> Hello Cong,
>
> did you have any time to look at it further? I'm just asking since my
> boss wants me to give him some verdict. I've started to study eBPF and
> XDP in the meantime so we have an alternative in case there won't be a
> solution to this problem.

Sorry for the delay. I lost connection to my dev machine, I am trying
to setup this on my own laptop.

Regarding to your test result above, I think I saw some difference
on my side, I have no idea why you didn't see any difference. Please
let me collect the data once I setup the test environment shortly today.

Thanks!