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Date: Wed, 10 May 2023 16:15:07 +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
Ok i will try to set CONFIG_HZ to 1000 and will make tests
Thanks Eric
> On 10 May 2023, at 12:40, Eric Dumazet <edumazet@...gle.com> wrote:
>
> On Wed, May 10, 2023 at 8:06 AM Martin Zaharinov <micron10@...il.com> wrote:
>>
>> I think problem is in this part of code in net/core/dev.c
>
> What makes you think this ?
>
> msleep() is not called a single time on my test bed.
>
> # perf probe -a msleep
> # cat bench.sh
> modprobe dummy 2>/dev/null
> ip link set dev dummy0 up 2>/dev/null
> 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 $(seq 2 4094); do ip link del link dummy0 name vlan$i
> type vlan id $i; done
>
> # perf record -e probe:msleep -a -g ./bench.sh
>
> real 0m59.877s
> user 0m0.588s
> sys 0m7.023s
> [ perf record: Woken up 6 times to write data ]
> [ perf record: Captured and wrote 8.561 MB perf.data ]
> # perf script
> # << empty, nothing >>
>
>
>
>
>> #define WAIT_REFS_MIN_MSECS 1
>> #define WAIT_REFS_MAX_MSECS 250
>> /**
>> * netdev_wait_allrefs_any - wait until all references are gone.
>> * @list: list of net_devices to wait on
>> *
>> * This is called when unregistering network devices.
>> *
>> * Any protocol or device that holds a reference should register
>> * for netdevice notification, and cleanup and put back the
>> * reference if they receive an UNREGISTER event.
>> * We can get stuck here if buggy protocols don't correctly
>> * call dev_put.
>> */
>> static struct net_device *netdev_wait_allrefs_any(struct list_head *list)
>> {
>> unsigned long rebroadcast_time, warning_time;
>> struct net_device *dev;
>> int wait = 0;
>>
>> rebroadcast_time = warning_time = jiffies;
>>
>> list_for_each_entry(dev, list, todo_list)
>> if (netdev_refcnt_read(dev) == 1)
>> return dev;
>>
>> while (true) {
>> if (time_after(jiffies, rebroadcast_time + 1 * HZ)) {
>> rtnl_lock();
>>
>> /* Rebroadcast unregister notification */
>> list_for_each_entry(dev, list, todo_list)
>> call_netdevice_notifiers(NETDEV_UNREGISTER, dev);
>>
>> __rtnl_unlock();
>> rcu_barrier();
>> rtnl_lock();
>>
>> list_for_each_entry(dev, list, todo_list)
>> if (test_bit(__LINK_STATE_LINKWATCH_PENDING,
>> &dev->state)) {
>> /* We must not have linkwatch events
>> * pending on unregister. If this
>> * happens, we simply run the queue
>> * unscheduled, resulting in a noop
>> * for this device.
>> */
>> linkwatch_run_queue();
>> break;
>> }
>>
>> __rtnl_unlock();
>>
>> rebroadcast_time = jiffies;
>> }
>>
>> if (!wait) {
>> rcu_barrier();
>> wait = WAIT_REFS_MIN_MSECS;
>> } else {
>> msleep(wait);
>> wait = min(wait << 1, WAIT_REFS_MAX_MSECS);
>> }
>>
>> list_for_each_entry(dev, list, todo_list)
>> if (netdev_refcnt_read(dev) == 1)
>> return dev;
>>
>> if (time_after(jiffies, warning_time +
>> READ_ONCE(netdev_unregister_timeout_secs) * HZ)) {
>> list_for_each_entry(dev, list, todo_list) {
>> pr_emerg("unregister_netdevice: waiting for %s to become free. Usage count = %d\n",
>> dev->name, netdev_refcnt_read(dev));
>> ref_tracker_dir_print(&dev->refcnt_tracker, 10);
>> }
>>
>> warning_time = jiffies;
>> }
>> }
>> }
>>
>>
>>
>> m.
>>
>>
>>> 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
>>
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