netdev - Re: Very slow remove interface from kernel

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Message-Id: <E187AF3F-CF56-408C-B89D-6CC99563D242@gmail.com>
Date: Wed, 10 May 2023 12:16:54 +0300
From: Martin Zaharinov <micron10@...il.com>
To: Ido Schimmel <idosch@...sch.org>
Cc: Eric Dumazet <edumazet@...gle.com>,
 netdev <netdev@...r.kernel.org>
Subject: Re: Very slow remove interface from kernel

Hi all 

one more update

i test with Proxmox direct  with kernel 6.2.6

modprobe dummy numdummies=1
ip link set dev dummy0 up
for i in $(seq 2 1999); do ip link add link dummy0 name vlan$i type vlan id $i; done
for i in $(seq 2 1999); do ip link set dev vlan$i up; done
 time for i in $(seq 2 1999); do ip link del link dummy0 name vlan$i type vlan id $i; done

real	1m6.308s
user	0m4.451s
sys	0m1.589s


This kernel is configured with CONFIG_HZ 250 and as you see i add 1998 vlans  if add 4094 is time up to 4-5 min to remove 

in test kernel i set CONFIG_HZ to 1000 but i dont this this is fine for any server.




> On 9 May 2023, at 23:08, Ido Schimmel <idosch@...sch.org> wrote:
> 
> On Tue, May 09, 2023 at 09:50:18PM +0300, Martin Zaharinov wrote:
>> 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
> 
> You are off-CPU most of the time, the question is what is blocking. I'm
> getting the following results with net-next:
> 
> # time -p for i in $(seq 2 4094); do ip link del dev eth0.$i; done
> real 177.09
> user 3.85
> sys 31.26
> 
> When using a batch file to perform the deletion:
> 
> # time -p ip -b vlan_del.batch 
> real 35.25
> user 0.02
> sys 3.61
> 
> And to check where we are blocked most of the time while using the batch
> file:
> 
> # ../bcc/libbpf-tools/offcputime -p `pgrep -nx ip`
> [...]
>    __schedule
>    schedule
>    schedule_timeout
>    wait_for_completion
>    rcu_barrier
>    netdev_run_todo
>    rtnetlink_rcv_msg
>    netlink_rcv_skb
>    netlink_unicast
>    netlink_sendmsg
>    ____sys_sendmsg
>    ___sys_sendmsg
>    __sys_sendmsg
>    do_syscall_64
>    entry_SYSCALL_64_after_hwframe
>    -                ip (3660)
>        25089479
> [...]
> 
> We are blocked for around 70% of the time on the rcu_barrier() in
> netdev_run_todo().
> 
> Note that one big difference between my setup and yours is that in my
> case eth0 is a dummy device and in your case it's probably a physical
> device that actually implements netdev_ops::ndo_vlan_rx_kill_vid(). If
> so, it's possible that a non-negligible amount of time is spent talking
> to hardware/firmware to delete the 4K VIDs from the device's VLAN
> filter.
> 
>> 
>> 
>> Config is very clean i remove big part of CONFIG options .
>> 
>> is there options to debug what is happen.
>> 
>> m