netdev - Query about the impact of using CONFIG_PREEMPT_RT on locking mechanisms within networking drivers

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Message-ID:
 <TYCPR01MB12093B8476E1B9EC33CBA4953C2E8A@TYCPR01MB12093.jpnprd01.prod.outlook.com>
Date: Wed, 15 Oct 2025 11:24:35 +0000
From: Fabrizio Castro <fabrizio.castro.jz@...esas.com>
To: "davem@...emloft.net" <davem@...emloft.net>, "edumazet@...gle.com"
	<edumazet@...gle.com>, "kuba@...nel.org" <kuba@...nel.org>,
	"pabeni@...hat.com" <pabeni@...hat.com>, "andrew@...n.ch" <andrew@...n.ch>,
	"bigeasy@...utronix.de" <bigeasy@...utronix.de>, "clrkwllms@...nel.org"
	<clrkwllms@...nel.org>, "rostedt@...dmis.org" <rostedt@...dmis.org>
CC: "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"linux-rt-devel@...ts.linux.dev" <linux-rt-devel@...ts.linux.dev>
Subject: Query about the impact of using CONFIG_PREEMPT_RT on locking
 mechanisms within networking drivers

Dear All,

We have recently started debugging some issues that only show up
with the kernel built with CONFIG_PREEMPT_RT=y, and we have noticed
some differences w.r.t. the non-RT version.

One of the major differences that we have noticed is that spin locks
basically become rtmutexes with the RT kernel, whereas they are mapped
to raw spin locks in non-RT kernels.

When is using raw spin locks directly in networking drivers considered
acceptable (if ever)?

Thank you for taking the time for reading this email, comments welcome.

Kind regards,
Fab