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Message-ID: <20230929162121.1822900-1-bigeasy@linutronix.de> Date: Fri, 29 Sep 2023 18:20:18 +0200 From: Sebastian Andrzej Siewior <bigeasy@...utronix.de> To: linux-kernel@...r.kernel.org, netdev@...r.kernel.org Cc: "David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, Peter Zijlstra <peterz@...radead.org>, Thomas Gleixner <tglx@...utronix.de>, Wander Lairson Costa <hawk@...nel.org> Subject: [PATCH net-next 0/2] net: Use SMP threads for backlog NAPI (or optional). 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. Changes: - RFC…v1 https://lore.kernel.org/all/20230818092111.5d86e351@kernel.org - Patch #2 has been removed. Removing the warning is still an option. - There are two patches in the series: - Patch #1 always creates backlog threads - Patch #2 creates the backlog threads if requested at boot time, mandatory on PREEMPT_RT. So it is either or and I wanted to show how both look like. - The kernel test robot reported a performance regression with loopback (stress-ng --udp X --udp-ops Y) against the RFC version. The regression is now avoided by using local-NAPI if backlog processing is requested on the local CPU. Sebastian
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