Message-ID: <CAF2d9jgUccznBGtouWs37Pttzbh3uFX3OdSsZ1dz0GS16ofv-A@mail.gmail.com>
Date:	Fri, 24 Apr 2015 15:40:29 -0700
From:	Mahesh Bandewar <maheshb@...gle.com>
To:	Dan Williams <dcbw@...hat.com>
Cc:	netdev <netdev@...r.kernel.org>,
	Eric Dumazet <edumazet@...gle.com>,
	David Miller <davem@...emloft.net>
Subject: Re: [PATCH next 1/3] ipvlan: Defer multicast / broadcast processing
 to a work-queue

On Fri, Apr 24, 2015 at 1:15 PM, Dan Williams <dcbw@...hat.com> wrote:
> On Thu, 2015-04-23 at 14:29 -0700, Mahesh Bandewar wrote:
>> Processing multicast / broadcast in fast path is performance draining
>> and having more links means more clonning and bringing performance
>> down further.
>>
>> Broadcast; in particular, need to be given to all the virtual links.
>> Earlier tricks of enabling broadcast bit for IPv4 only interfaces are not
>> really working since it fails autoconf. Which means enabling braodcast
>> for all the links if protocol specific hacks do not have to be added into
>> the driver.
>>
>> This patch defers all (incoming as well as outgoing) multicast traffic to
>> a work-queue leaving only the unicast traffic in the fast-path. Now if we
>> need to apply any additional tricks to further reduce the impact of this
>> (multicast / broadcast) type of traffic, it can be implemented while
>> processing this work without affecting the fast-path.
>
> These patches appear to work for me for the L2 + DHCP use-case, however
> I experienced some quite odd behavior when pinging the ipvlan interface
> from another machine.  I did this:
>
> ip link add link eno1 type ipvlan mode l2
> ip netns add ipv
> ip link set dev ipvlan0 netns ipv
> ip netns exec ipv /sbin/dhclient -B -4 -1 -v
> -pf /run/dhclient-ipvlan0.pid -C adafdasdfasf ipvlan0
> ip netns exec ping 4.2.2.1 <success>
>
> However, when pinging from another machine, I got very inconsistent ping
> replies:
>
> 64 bytes from 192.168.1.38: icmp_seq=1 ttl=64 time=11.4 ms
> 64 bytes from 192.168.1.38: icmp_seq=16 ttl=64 time=64.9 ms
> 64 bytes from 192.168.1.38: icmp_seq=25 ttl=64 time=87.9 ms
> 64 bytes from 192.168.1.38: icmp_seq=30 ttl=64 time=242 ms
> 64 bytes from 192.168.1.38: icmp_seq=35 ttl=64 time=40.1 ms
> 64 bytes from 192.168.1.38: icmp_seq=36 ttl=64 time=60.9 ms
>
We know that there is that PAUSE frame leak but that should not cause
this behavior if those are present in your network. The sched_work()
which is wrong (as pointed by Eric) especially when the machine is
busy and that might trigger something like this. Almost every 10th -
15th ping packet seems to be processed correctly.

I did get consistent results as opposed what you have shown here, but
will dig some more to see if something obviously wrong here.

> But I cannot reproduce that in a second run (though I haven't rebooted
> to test cleanly again).
>
> And oddly, the dhclient process takes a consistent 5% CPU and wireshark
> running on eno1 (not even the ipvlan interface) jumps to 100% CPU along
> with the dumpcap process taking another 25%, none of which are normal.
> This is a 4-core i4790 box, so something is wrong here; is something
> holding onto a spinlock for way too long?
>
> But at least it handles the packets ok, so I say progress!  Happy to
> help track down the CPU usage issue if you want to give me patches to
> test.
>
Which patch(es) you are referring to?

> Dan
>
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