Den 2020-11-23 kl. 23:30, skrev Jakub Kicinski:
On Mon, 23 Nov 2020 14:22:31 +0000 Thomas Karlsson wrote:
Hello,
There is a special queue handling in macvlan.c for broadcast and
multicast packages that was arbitrarily set to 1000 in commit
07d92d5cc977a7fe1e683e1d4a6f723f7f2778cb . While this is probably
sufficient for most uses cases it is insufficient to support high
packet rates. I currently have a setup with 144 000 multicast packets
incoming per second (144 different live audio RTP streams) and suffer
very frequent packet loss. With unicast this is not an issue and I
can in addition to the 144kpps load the macvlan interface with
another 450mbit/s using iperf.
In order to verify that the queue is the problem I edited the define
to 100000 and recompiled the kernel module. After replacing it with
rmmod/insmod I get 0 packet loss (measured over 2 days where I before
had losses every other second or so) and can also load an additional
450 mbit/s multicast traffic using iperf without losses. So basically
no change in performance between unicast/multicast when it comes to
lost packets on my machine.
I think It would be best if this queue length was configurable
somehow. Either an option when creating the macvlan (like how
bridge/passthrough/etc are set) or at least when loading the module
(for instance by using a config in /etc/modprobe.d). One size does
not fit all in this situation.
The former please. You can add a netlink attribute, should be
reasonably straightforward. The other macvlan attrs are defined
under "MACVLAN section" in if_link.h.
I did some work towards a patch using the first option,
by adding a netlink attribute in if_link.h as suggested.
I agree that this was reasonably straightforward, until userspace.
In order to use/test my new parameter I need to update iproute2 package
as far as I understand. But then since I use the macvlan with docker
I also need to update the docker macvlan driver to send this new
option to the kernel module.
For this reason I would like to know if you would consider
merging a patch using the module_param(...) variant instead?
I would argue that this still makes the situation better
and resolves the packet-loss issue, although not necessarily
in an optimal way. However, The upside of being able to specify the
parameter on a per macvlan interface level instead of globally is not
that big in this situation. Normally you don't use that much
multicast anyway so it's a parameter that only will be touched by
a very small user base that can understand and handle the implications
of such a global setting.
