Re: Scalability of interface creation and deletion

Paul,

quoted

Yes, really 20-49us and 50-99us, not ms. Raw data attached :-)

I'm guessing there are circumstances where there is an early exit.

Well, if you were onlining and offlining CPUs, then if there was only
one CPU online, this could happen.

No, I wasn't doing that.

 And there really is only one CPU
online during boot, so if your measurements included early boot time,
this could easily explain these very short timings.

No, I waited a few minutes after boot for the system to stabilize, and
all CPUs were definitely online.

The patch to the kernel I am running is below.

quoted

There is nothing much going on these systems (idle, no other users,
just normal system daemons).

And normal system daemons might cause this, right?

Yes. Everything is normal, except I did
 service udev stop
 unshare -n bash
which together stop the system running interface scripts when
interfaces are created (as upstart and upstart-udev-bridge are
now integrated, you can't kill upstart, so you have to rely on
unshare -n to stop the events being propagated). That's just
to avoid measuring the time it takes to execute the scripts.

-- 
Alex Bligh

diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index dd4aea8..e401018 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c

@@ -1518,6 +1518,7 @@ EXPORT_SYMBOL_GPL(call_rcu_bh);
 void synchronize_sched(void)
 {
        struct rcu_synchronize rcu;
+       ktime_t time_start = ktime_get();

        if (rcu_blocking_is_gp())
                return;

@@ -1529,6 +1530,7 @@ void synchronize_sched(void)
        /* Wait for it. */
        wait_for_completion(&rcu.completion);
        destroy_rcu_head_on_stack(&rcu.head);
+       pr_err("synchronize_sched() in %lld us\n", 

ktime_us_delta(ktime_get(), time_start));
 }
 EXPORT_SYMBOL_GPL(synchronize_sched);

diff --git a/net/core/dev.c b/net/core/dev.c
index 856b6ee..013f627 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c

@@ -5164,7 +5164,9 @@ static void rollback_registered_many(struct list_head 

*head)
        dev = list_first_entry(head, struct net_device, unreg_list);
        call_netdevice_notifiers(NETDEV_UNREGISTER_BATCH, dev);

+       pr_err("begin rcu_barrier()\n");
        rcu_barrier();
+       pr_err("end rcu_barrier()\n");

        list_for_each_entry(dev, head, unreg_list)
                dev_put(dev);

@@ -5915,8 +5917,10 @@ EXPORT_SYMBOL(free_netdev);
  */
 void synchronize_net(void)
 {
+       pr_err("begin synchronize_net()\n");
        might_sleep();
        synchronize_rcu();
+       pr_err("end synchronize_net()\n");
 }
 EXPORT_SYMBOL(synchronize_net);