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Date: Wed, 10 May 2023 11:40:39 +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 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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