netdev - Re: Very slow remove interface from kernel

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Message-Id: <FE7CE62C-DBEB-4FE1-8ACB-C8B7DAF15710@gmail.com>
Date: Tue, 9 May 2023 21:50:18 +0300
From: Martin Zaharinov <micron10@...il.com>
To: Eric Dumazet <edumazet@...gle.com>
Cc: Ido Schimmel <idosch@...sch.org>,
 netdev <netdev@...r.kernel.org>
Subject: Re: Very slow remove interface from kernel

Hi Eric

i try on kernel 6.3.1 


time for i in $(seq 2 4094); do ip link del link eth1 name vlan$i type vlan id $i; done

real	4m51.633s  —— here i stop with Ctrl + C  -  and rerun  and second part finish after 3 min
user	0m7.479s
sys	0m0.367s


Config is very clean i remove big part of CONFIG options .

is there options to debug what is happen.

m


> On 9 May 2023, at 15:36, Eric Dumazet <edumazet@...gle.com> wrote:
> 
> 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.
>> 
>>