linux-kernel - Re: [PATCH net-next 2/2] net: dsa: mv88e6xxx: implement egress tbf qdisc for 6393x family

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <bb799b06-8ca8-8a29-3873-af09c859ae88@bootlin.com>
Date:   Fri, 9 Jun 2023 19:38:13 +0200
From:   Alexis Lothoré <alexis.lothore@...tlin.com>
To:     Andrew Lunn <andrew@...n.ch>
Cc:     Florian Fainelli <f.fainelli@...il.com>,
        Vladimir Oltean <olteanv@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>, linux-kernel@...r.kernel.org,
        netdev@...r.kernel.org,
        Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
        paul.arola@...us.com, scott.roberts@...us.com
Subject: Re: [PATCH net-next 2/2] net: dsa: mv88e6xxx: implement egress tbf
 qdisc for 6393x family

On 6/9/23 19:16, Andrew Lunn wrote:
>> Yes, I can do that (or maybe -EINVAL to match Vladimir's comment ?). I think
>> it's worth mentioning that I encountered an issue regarding those values during
>> tests: I use tc program to set the tbf, and I observed that tc does not even
>> reach kernel to set the qdisc if we pass no burst/latency value OR if we set it
>> to 0. So tc enforces right on userspace side non-zero value for those
>> parameters, and I have passed random values and ignored them on kernel side.
> 
> That is not good. Please take a look around and see if any other
> driver offloads TBF, and what they do with burst.
> 
>> Checking available doc about tc-tbf makes me feel like that indeed a TBF qdisc
>> command without burst or latency value makes no sense, except my use case can
>> not have such values. That's what I struggled a bit to find a proper qdisc to
>> match hardware cap. I may fallback to a custom netlink program to improve testing.
> 
> We don't really want a custom application, since we want users to use
> TC to set this up.
> 
> Looking at the 6390 datasheet, Queue Counter Registers, mode 8 gives
> the number of egress buffers for a port. You could validate that the
> switch has at least the requested number of buffers assigned to the
> port? There is quite a bit you can configure, so maybe there is a way
> to influence the number of buffers, so you can actually implement the
> burst parameter?

Thanks for the pointers. I will check the egress buffers configuration and see
if I can come up with something better

> 
>       Andrew

-- 
Alexis Lothoré, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com