netdev - Re: Very slow remove interface from kernel

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Message-ID: <CANn89iKOm2WPoemiqCsWaMXMyGf9C5xXH=NaSidPSNCpKxf_jQ@mail.gmail.com>
Date: Tue, 9 May 2023 14:36:06 +0200
From: Eric Dumazet <edumazet@...gle.com>
To: Martin Zaharinov <micron10@...il.com>
Cc: Ido Schimmel <idosch@...sch.org>, netdev <netdev@...r.kernel.org>
Subject: Re: Very slow remove interface from kernel

On Tue, May 9, 2023 at 1:10 PM Martin Zaharinov <micron10@...il.com> wrote:
>
> Hi
>
> in short, there is no way to make the kernel do it faster.

Make sure your kernel does not include options you do not need.

>
> Before time with old kernel unregister device make more faster .
>
> with latest kernel >6.x this make very slow .
>

Yup, I feel your pain.

Maybe you should start a bisection then...

You might find that you have some CONFIG_ option that makes this
operation very slow.

Some layers (like hamradio and others) lack batch operations in their
netdev removal handlers.

For instance, on one machine I have access to and with my standard
.config, your benchmark gives a not too bad result with pristine
linux-6.3

modprobe dummy
ip link set dev dummy0 up
for i in $(seq 2 4094); do ip link add link dummy0 name vlan$i type
vlan id $i; done
for i in $(seq 2 4094); do ip link set dev vlan$i up; done
time for i in $(seq 2 4094); do ip link del link eth1 name vlan$i type
vlan id $i; done
real 0m55.808s
user 0m0.788s
sys 0m6.868s

Without batching, I think one netdev removal needs three synchronize_net() calls

I am reasonably certain numbers would not look so good if I booted a
"make allyesconfig" kernel.








>
> is there any chance to try to make this more fast.
>
>
> m.
>
>
> > On 9 May 2023, at 13:32, Eric Dumazet <edumazet@...gle.com> wrote:
> >
> > On Tue, May 9, 2023 at 12:20 PM Ido Schimmel <idosch@...sch.org> wrote:
> >>
> >> On Tue, May 09, 2023 at 11:22:13AM +0300, Martin Zaharinov wrote:
> >>> add vlans :
> >>> for i in $(seq 2 4094); do ip link add link eth1 name vlan$i type vlan id $i; done
> >>> for i in $(seq 2 4094); do ip link set dev vlan$i up; done
> >>>
> >>>
> >>> and after that run :
> >>>
> >>> for i in $(seq 2 4094); do ip link del link eth1 name vlan$i type vlan id $i; done
> >>>
> >>>
> >>> time for remove for this 4093 vlans is 5-10 min .
> >>>
> >>> Is there options to make fast this ?
> >>
> >> If you know you are going to delete all of them together, then you can
> >> add them to the same group during creation:
> >>
> >> for i in $(seq 2 4094); do ip link add link eth1 name vlan$i up group 10 type vlan id $i; done
> >>
> >> Then delete the group:
> >>
> >> ip link del group 10
> >>
> >
> > Another way is to create a netns for retiring devices,
> > move devices to the 'retirens' when they need to go away.
> >
> > Then once per minute, delete the retirens and create a new one.
> >
> > -> This batches netdev deletions.
> >
> >
> >> IIRC, in the past there was a patchset to allow passing a list of
> >> ifindexes instead of a group number, but it never made its way upstream.
>
>