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Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Peter Zijlstra , Thomas Gleixner , Wander Lairson Costa Subject: [PATCH net-next 0/2] net: Use SMP threads for backlog NAPI (or optional). Date: Fri, 29 Sep 2023 18:20:18 +0200 Message-ID: <20230929162121.1822900-1-bigeasy@linutronix.de> MIME-Version: 1.0 X-Spam-Status: No, score=-0.9 required=5.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS autolearn=unavailable autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on agentk.vger.email Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org X-Greylist: Sender passed SPF test, not delayed by milter-greylist-4.6.4 (agentk.vger.email [0.0.0.0]); Fri, 29 Sep 2023 09:21:54 -0700 (PDT) X-getmail-retrieved-from-mailbox: INBOX X-GMAIL-THRID: 1778410794499051243 X-GMAIL-MSGID: 1778410794499051243 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