netdev - Re: Bypass qdiscs?

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Message-ID: <29217dab-e00e-4e4c-8d6a-4088d8e79c8e@lunn.ch>
Date: Sat, 4 Nov 2023 16:08:11 +0100
From: Andrew Lunn <andrew@...n.ch>
To: John Ousterhout <ouster@...stanford.edu>
Cc: netdev@...r.kernel.org
Subject: Re: Bypass qdiscs?

On Fri, Nov 03, 2023 at 04:55:35PM -0700, John Ousterhout wrote:
> Is there a way to mark an skb (or its socket) before invoking
> ip_queue_xmit/ip6_xmit so that the packet will bypass the qdiscs and
> be transmitted immediately? Is doing such a thing considered bad
> practice?
> 
> (Homa has its own packet scheduling mechanism so the qdiscs are just
> getting in the way and adding delays)

Hi John

One thing to think about is what happens when hardware starts
supporting Homa. Can the packet scheduling be moved into the hardware?
Ideally you want to make use of the existing mechanisms to offload
scheduling to the hardware, rather than add a Homa specific one.

Did you try adding a Homa specific qdisc implementing the scheduling
algorithm? Did it kill performance? We prefer to try to fix problems,
rather than bypass them.

       Andrew