netdev - Re: dsa traffic priorization

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Message-ID: <20190919083638.wgxrrgtqxwpjcsu3@pengutronix.de>
Date:   Thu, 19 Sep 2019 10:36:38 +0200
From:   Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>
To:     Sascha Hauer <s.hauer@...gutronix.de>
Cc:     Vladimir Oltean <olteanv@...il.com>,
        netdev <netdev@...r.kernel.org>,
        Vivien Didelot <vivien.didelot@...oirfairelinux.com>,
        Florian Fainelli <f.fainelli@...il.com>, kernel@...gutronix.de,
        Andrew Lunn <andrew@...n.ch>
Subject: Re: dsa traffic priorization

On Thu, Sep 19, 2019 at 10:00:51AM +0200, Sascha Hauer wrote:
> Hi Vladimir,
> 
> On Wed, Sep 18, 2019 at 05:36:08PM +0300, Vladimir Oltean wrote:
> > Hi Sascha,
> > 
> > On Wed, 18 Sep 2019 at 17:03, Sascha Hauer <s.hauer@...gutronix.de> wrote:
> > >
> > > Hi All,
> > >
> > > We have a customer using a Marvell 88e6240 switch with Ethercat on one port and
> > > regular network traffic on another port. The customer wants to configure two things
> > > on the switch: First Ethercat traffic shall be priorized over other network traffic
> > > (effectively prioritizing traffic based on port). Second the ethernet controller
> > > in the CPU is not able to handle full bandwidth traffic, so the traffic to the CPU
> > > port shall be rate limited.
> > >
> > 
> > You probably already know this, but egress shaping will not drop
> > frames, just let them accumulate in the egress queue until something
> > else happens (e.g. queue occupancy threshold triggers pause frames, or
> > tail dropping is enabled, etc). Is this what you want?
> 
> If I understand correctly then the switch has multiple output queues per
> port. The Ethercat traffic will go to a higher priority queue and on
> congestion on other queues, frames designated for that queue will be
> dropped. I just talked to our customer and he verified that their
> Ethercat traffic still goes through even when the ports with the general
> traffic are jammed with packets. So yes, I think this is what I want.

Moreover egressing the cpu port has the advantage that network
participants on other ports that might be able to process packet quicker
are not limited.

Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |