netdev - Re: [PATCH v2 net-next 0/7] dpaa2-eth: add support for Rx traffic classes

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Message-ID: <20200515152500.158ca070@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com>
Date:   Fri, 15 May 2020 15:25:00 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     Ioana Ciornei <ioana.ciornei@....com>
Cc:     "davem@...emloft.net" <davem@...emloft.net>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [PATCH v2 net-next 0/7] dpaa2-eth: add support for Rx traffic
 classes

On Fri, 15 May 2020 20:48:27 +0000 Ioana Ciornei wrote:
> > > There is no input taken from the user at the moment. The traffic class
> > > id is statically selected based on the VLAN PCP field. The
> > > configuration for this is added in patch 3/7.  
> > 
> > Having some defaults for RX queue per TC is understandable. But patch 1
> > changes how many RX queues are used in the first place. Why if user does not
> > need RX queues per TC?  
> 
> In DPAA2 we have a boot time configurable system in which the user can select
> for each interface how many queues and how many traffic classes it needs.

Looking at the UG online DPNI_CREATE has a NUM_RX_TCS param. You're not
using that for the kernel driver?

> The driver picks these up from firmware and configures the traffic class
> distribution only if there is more than one requested.
> With one TC the behavior of the driver is exactly as before.

This configuring things statically via some direct FW interface when
system boots really sounds like a typical "using Linux to boot a
proprietary networking stack" scenario.

With the Rx QoS features users won't even be able to tell via standard
Linux interfaces what the config was.