From mboxrd@z Thu Jan 1 00:00:00 1970 From: Sebastian Andrzej Siewior Subject: Re: INFO: rcu_preempt detected stalls on CPUs/tasks Date: Fri, 29 Jul 2016 18:46:58 +0200 Message-ID: <20160729164658.GH21715@linutronix.de> References: <20160714152703.GA12152@linutronix.de> <150d1d1f-b427-50be-524d-dbe80dd5523e@ginzinger.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Cc: "linux-rt-users@vger.kernel.org" To: Henri Roosen Return-path: Received: from Galois.linutronix.de ([146.0.238.70]:52007 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751695AbcG2QrA (ORCPT ); Fri, 29 Jul 2016 12:47:00 -0400 Content-Disposition: inline In-Reply-To: <150d1d1f-b427-50be-524d-dbe80dd5523e@ginzinger.com> Sender: linux-rt-users-owner@vger.kernel.org List-ID: * Henri Roosen | 2016-07-15 12:54:25 [+0200]: >The problem is easily triggered, but only after starting a flood-ping to >the PREEMPT_RT-system under test. This also results in huge latency, >much bigger than on a 'normal' PREEMPT-system, which seems to be >resistant against the flood-ping. > >Any suggestions how to best trace this down? Hmm. 4.1.27-rt30 has softirq: split timer softirqs out of ksoftirqd net: provide a way to delegate processing a softirq to ksoftirqd I would suggest using those two but you should have them. Your ksoftirqd runs as SCHED_OTHER, right? And you do have CONFIG_RCU_BOOST enabled? Your do_hell script which starts hackbench does not run with higher priority? >>From the backtrace it is hackbench "doing things" and this one should be preempted by RCU and ethernet networking napi code should be preempted / moved to ksoftirqd during the flood-ping. Can you check this happens? >Thanks, >Henri Sebastian