netdev - Re: Hardcoded multicast queue length in macvlan.c driver causes poor multicast receive performance

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Date:   Fri, 27 Nov 2020 09:27:05 -0800
From:   Jakub Kicinski <kuba@...nel.org>
To:     Thomas Karlsson <thomas.karlsson@...eda.se>
Cc:     "davem@...emloft.net" <davem@...emloft.net>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        jiri@...nulli.us, kaber@...sh.net, edumazet@...gle.com,
        vyasevic@...hat.com, alexander.duyck@...il.com
Subject: Re: Hardcoded multicast queue length in macvlan.c driver causes
 poor multicast receive performance

On Thu, 26 Nov 2020 21:00:46 +0100 Thomas Karlsson wrote:
> On 2020-11-26 00:01, Jakub Kicinski wrote:
> > On Wed, 25 Nov 2020 23:15:39 +0100 Thomas Karlsson wrote:  
> >> Or is there a way to set the parameters in a more "raw" form that
> >> does not require a patch to iproute2 with parameter parsing, error
> >> handing, man pages updates, etc. I feel that I'm getting in over my
> >> head here.  
> > 
> > We're here to assist! Netlink takes a little bit of effort 
> > to comprehend but it's very simple once you get the mechanics!
> >   
> 
> Thanks for the encouragement, I have been able to build iproute2 today and
> I am successfully communicating with the driver now being able to set and retrieve my queue len!
> 
> As I'm working on this I do got a question. I placed the bc_queue_len into the struct macvlan_port *port
> since that is where the bc_queue is located today. But when I change and retrieve the queue from userspace I realize
> that all macvlan interfaces that share the same physical lowerdev uses the same port structure and thus
> the same bc_queue_len.

Indeed looks like its an ingress attribute.

> It confused me at first and I'm not sure if that is how it should be. I expected the driver to have different
> bc_queues for all macvlan interfaces no matter which lowerdev they were using but obviously that is not the case.
> 
> It may be a bit confusing to change bc_queue_len on one macvlan and see that the change was applied to more than one.
> 
> But I'm not sure if I should just move bc_queue_len to the struct macvlan_dev either. because then different macvlans will use different queue lengths while they still use the same queue. Which may also be considered a bit illogical
> 
> Let me know what you prefer here!

I'd record the queue len requested by each interface in their struct
macvlan_dev and then calculate a max over the members to set the actual
value in struct macvlan_port.

Let me CC some extra people, looks like macvlan does not have a
maintainer..