netdev - Re: [v2 2/9] dpaa_eth: add support for DPAA Ethernet

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Date:	Sat, 08 Aug 2015 10:38:34 -0700
From:	Florian Fainelli <f.fainelli@...il.com>
To:	madalin.bucur@...escale.com, netdev@...r.kernel.org
CC:	linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
	davem@...emloft.net, scottwood@...escale.com,
	igal.liberman@...escale.com, ppc@...dchasers.com, joe@...ches.com,
	pebolle@...cali.nl, joakim.tjernlund@...nsmode.se
Subject: Re: [v2 2/9] dpaa_eth: add support for DPAA Ethernet

Le 08/05/15 08:41, Madalin Bucur a écrit :
> This introduces the Freescale Data Path Acceleration Architecture
> (DPAA) Ethernet driver (dpaa_eth) that builds upon the DPAA QMan,
> BMan, PAMU and FMan drivers to deliver Ethernet connectivity on
> the Freescale DPAA QorIQ platforms.
> 
> Signed-off-by: Madalin Bucur <madalin.bucur@...escale.com>
> ---
[snip]
> +
> +if FSL_DPAA_ETH
> +
> +config FSL_DPAA_CS_THRESHOLD_1G
> +	hex "Egress congestion threshold on 1G ports"
> +	range 0x1000 0x10000000
> +	default "0x06000000"

This sounds like something you would want to be able to configure at
runtime, either via private sysfs attributes, or better, using ethtool
and either a newly introduced set of tunables, or creating a private
driver API for this.

> +	---help---
> +	  The size in bytes of the egress Congestion State notification threshold on 1G ports.
> +	  The 1G dTSECs can quite easily be flooded by cores doing Tx in a tight loop
> +	  (e.g. by sending UDP datagrams at "while(1) speed"),
> +	  and the larger the frame size, the more acute the problem.
> +	  So we have to find a balance between these factors:
> +	       - avoiding the device staying congested for a prolonged time (risking
> +                 the netdev watchdog to fire - see also the tx_timeout module param);
> +               - affecting performance of protocols such as TCP, which otherwise
> +	         behave well under the congestion notification mechanism;
> +	       - preventing the Tx cores from tightly-looping (as if the congestion
> +	         threshold was too low to be effective);
> +	       - running out of memory if the CS threshold is set too high.
> +
> +config FSL_DPAA_CS_THRESHOLD_10G
> +	hex "Egress congestion threshold on 10G ports"
> +	range 0x1000 0x20000000
> +	default "0x10000000"
> +	---help ---
> +	  The size in bytes of the egress Congestion State notification threshold on 10G ports.
> +
> +config FSL_DPAA_INGRESS_CS_THRESHOLD
> +	hex "Ingress congestion threshold on FMan ports"
> +	default "0x10000000"
> +	---help---
> +	  The size in bytes of the ingress tail-drop threshold on FMan ports.
> +	  Traffic piling up above this value will be rejected by QMan and discarded by FMan.

Same here.
-- 
Florian
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