netdev - Re: [PATCH net-next] net: don't set sw irq coalescing defaults in case of PREEMPT

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Message-ID: <87535ce9-4780-d982-0535-d010720aa636@gmail.com>
Date: Wed, 31 May 2023 10:18:40 +0200
From: Heiner Kallweit <hkallweit1@...il.com>
To: Jakub Kicinski <kuba@...nel.org>
Cc: David Miller <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>,
 Paolo Abeni <pabeni@...hat.com>,
 "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [PATCH net-next] net: don't set sw irq coalescing defaults in
 case of PREEMPT_RT

On 31.05.2023 08:30, Jakub Kicinski wrote:
> On Sun, 28 May 2023 19:39:59 +0200 Heiner Kallweit wrote:
>> If PREEMPT_RT is set, then assume that the user focuses on minimum
>> latency. Therefore don't set sw irq coalescing defaults.
>> This affects the defaults only, users can override these settings
>> via sysfs.
> 
> Did someone complain? I don't have an opinion, but I'm curious what
> prompted the patch.

No direct complain, and not covering exactly this point.
Background: I witnessed some discussions between PREEMPT_RT users
(e.g. from linuxcnc project) regarding network latency with
RTL8168 NICs. It seems these users aren't really aware of the
userspace knobs that the kernel provides for RT optimization.
To make their life easier we could optimize few things for latency
and use PREEMPT_RT as an indicator.