linux-kernel - Re: [PATCH net-next 2/3] net: ethernet: ti: cpsw_new: enable broadcast/multicast rate limit support

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Message-ID: <20201114190909.cc3rlnvom6wf2zkg@skbuf>
Date:   Sat, 14 Nov 2020 21:09:09 +0200
From:   Vladimir Oltean <olteanv@...il.com>
To:     Grygorii Strashko <grygorii.strashko@...com>
Cc:     "David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org,
        Jakub Kicinski <kuba@...nel.org>,
        Vignesh Raghavendra <vigneshr@...com>,
        Sekhar Nori <nsekhar@...com>, linux-kernel@...r.kernel.org,
        linux-omap@...r.kernel.org, Tony Lindgren <tony@...mide.com>
Subject: Re: [PATCH net-next 2/3] net: ethernet: ti: cpsw_new: enable
 broadcast/multicast rate limit support

On Sat, Nov 14, 2020 at 05:56:53AM +0200, Grygorii Strashko wrote:
> This patch enables support for ingress broadcast(BC)/multicast(MC) rate limiting
> in TI CPSW switchdev driver (the corresponding ALE support was added in previous
> patch) by implementing HW offload for simple tc-flower policer with matches
> on dst_mac:
>  - ff:ff:ff:ff:ff:ff has to be used for BC rate limiting
>  - 01:00:00:00:00:00 fixed value has to be used for MC rate limiting
> 
> Hence tc policer defines rate limit in terms of bits per second, but the
> ALE supports limiting in terms of packets per second - the rate limit
> bits/sec is converted to number of packets per second assuming minimum
> Ethernet packet size ETH_ZLEN=60 bytes.
> 
> Examples:
> - BC rate limit to 1000pps:
>   tc qdisc add dev eth0 clsact
>   tc filter add dev eth0 ingress flower skip_sw dst_mac ff:ff:ff:ff:ff:ff \
>   action police rate 480kbit burst 64k
> 
>   rate 480kbit - 1000pps * 60 bytes * 8, burst - not used.
> 
> - MC rate limit to 20000pps:
>   tc qdisc add dev eth0 clsact
>   tc filter add dev eth0 ingress flower skip_sw dst_mac 01:00:00:00:00:00 \
>   action police rate 9600kbit burst 64k
> 
>   rate 9600kbit - 20000pps * 60 bytes * 8, burst - not used.
> 
> Signed-off-by: Grygorii Strashko <grygorii.strashko@...com>
> ---

Your example for multicast would actually be correct if you specified
the mask as well. Like this:

tc filter add dev eth0 ingress flower skip_sw \
	dst_mac 01:00:00:00:00:00/01:00:00:00:00:00 \
	action police rate 9600kbit burst 64k

But as things stand, the flow rule would have a certain meaning in
software (rate-limit only that particular multicast MAC address) and a
different meaning in hardware. Please modify the driver code to also
match on the mask.