netdev - Re: iproute2: tc deletion freezes whole server

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Date:   Tue, 5 May 2020 10:46:05 +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 Mon, May 4, 2020 at 7:46 PM Cong Wang <xiyou.wangcong@...il.com> wrote:
>
> Sorry for the delay. I lost connection to my dev machine, I am trying
> to setup this on my own laptop.

Sorry to hear that. I will gladly give you access to my testing
machine where all this nasty stuff happens every time so you can test
it in place. You can try everything there and have online results. I
can give you access even to the IPMI console so you can switch the
kernel during boot easily. I didn't notice this problem until the time
of deployment. My prior testing machines were with metallic ethernet
ports only so I didn't know about those problems earlier.

> On Mon, May 4, 2020 at 10:36 PM Cong Wang <xiyou.wangcong@...il.com> wrote:
> >
> > 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.

I saw some improvement too. It was more than 1.5s faster. Yet it was
still over 21s. I measured it with perf trace, not with time. I'll try
it the same way as you did.

>
> I tried to emulate your test case in my VM, here is the script I use:
>
> ====
> ip li set dev dummy0 up
> tc qd add dev dummy0 root handle 1: htb default 1
> for i in `seq 1 1000`
> do
>   tc class add dev dummy0 parent 1:0 classid 1:$i htb rate 1mbit ceil 1.5mbit
>   tc qd add dev dummy0 parent 1:$i fq_codel
> done
>
> time tc qd del dev dummy0 root
> ====
>
> And this is the result:
>
>     Before my patch:
>      real   0m0.488s
>      user   0m0.000s
>      sys    0m0.325s
>
>     After my patch:
>      real   0m0.180s
>      user   0m0.000s
>      sys    0m0.132s

My results with your test script.

before patch:
/usr/bin/time -p tc qdisc del dev enp1s0f0 root
real 1.63
user 0.00
sys 1.63

after patch:
/usr/bin/time -p tc qdisc del dev enp1s0f0 root
real 1.55
user 0.00
sys 1.54

> This is an obvious improvement, so I have no idea why you didn't
> catch any difference.

We use hfsc instead of htb. I don't know whether it may cause any
difference. I can provide you with my test scripts if necessary.

Thank you.