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Date: Mon, 14 Aug 2023 11:24:21 -0700
From: Jakub Kicinski <kuba@kernel.org>
To: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: linux-kernel@vger.kernel.org, netdev@vger.kernel.org, "David S. Miller"
 <davem@davemloft.net>, Eric Dumazet <edumazet@google.com>, Paolo Abeni
 <pabeni@redhat.com>, Peter Zijlstra <peterz@infradead.org>, Thomas Gleixner
 <tglx@linutronix.de>, Wander Lairson Costa <wander@redhat.com>
Subject: Re: [RFC PATCH net-next 0/2] net: Use SMP threads for backlog NAPI.
Message-ID: <20230814112421.5a2fa4f6@kernel.org>
In-Reply-To: <20230814093528.117342-1-bigeasy@linutronix.de>
References: <20230814093528.117342-1-bigeasy@linutronix.de>
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On Mon, 14 Aug 2023 11:35:26 +0200 Sebastian Andrzej Siewior wrote:
> The RPS code and "deferred skb free" both send IPI/ function call
> to a remote CPU in which a softirq is raised. This leads to a warning on
> PREEMPT_RT because raising softiqrs from function call led to undesired
> behaviour in the past. I had duct tape in RT for the "deferred skb free"
> and Wander Lairson Costa reported the RPS case.

Could you find a less invasive solution?
backlog is used by veth == most containerized environments.
This change has a very high risk of regression for a lot of people.