netdev - Re: Bypass qdiscs?

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Message-ID: <56f87c0304f8e4398d314992d1d872a7772eec9a.camel@inf.elte.hu>
Date: Sat, 04 Nov 2023 10:24:10 +0100
From: Ferenc Fejes <fejes@....elte.hu>
To: John Ousterhout <ouster@...stanford.edu>, netdev@...r.kernel.org
Subject: Re: Bypass qdiscs?

Hi!

On Fri, 2023-11-03 at 16:55 -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?

I'm not aware if we have such thing aside from the AF_PACKET's flag 
PACKET_QDISC_BYPASS [1,2]. I think the function packet_xmit [3]
utilizing that flag can be reused for your needs as well.

> 
> (Homa has its own packet scheduling mechanism so the qdiscs are just
> getting in the way and adding delays)
> 
> -John-

Best,
Ferenc

[1] https://man7.org/linux/man-pages/man7/packet.7.html
[2]
https://elixir.bootlin.com/linux/v6.6/source/net/packet/af_packet.c#L4026
[3]
https://elixir.bootlin.com/linux/v6.6/source/net/packet/af_packet.c#L273