From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1760280AbcBYJnY (ORCPT ); Thu, 25 Feb 2016 04:43:24 -0500 Received: from casper.infradead.org ([85.118.1.10]:55815 "EHLO casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751434AbcBYJnX (ORCPT ); Thu, 25 Feb 2016 04:43:23 -0500 Date: Thu, 25 Feb 2016 10:43:17 +0100 From: Peter Zijlstra To: "Paul E. McKenney" Cc: linux-kernel@vger.kernel.org, mingo@kernel.org, jiangshanlai@gmail.com, dipankar@in.ibm.com, akpm@linux-foundation.org, mathieu.desnoyers@efficios.com, josh@joshtriplett.org, tglx@linutronix.de, rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com, dvhart@linux.intel.com, fweisbec@gmail.com, oleg@redhat.com, bobby.prani@gmail.com Subject: Re: [PATCH tip/core/rcu 03/13] rcu: Stop treating in-kernel CPU-bound workloads as errors Message-ID: <20160225094317.GN6356@twins.programming.kicks-ass.net> References: <20160224051221.GA17099@linux.vnet.ibm.com> <1456290770-18659-3-git-send-email-paulmck@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1456290770-18659-3-git-send-email-paulmck@linux.vnet.ibm.com> User-Agent: Mutt/1.5.21 (2012-12-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Feb 23, 2016 at 09:12:40PM -0800, Paul E. McKenney wrote: > Commit 4a81e8328d379 ("Reduce overhead of cond_resched() checks for RCU") > handles the error case where a nohz_full loops indefinitely in the kernel > with the scheduling-clock interrupt disabled. However, this handling > includes IPIing the CPU running the offending loop, which is not what > we want for real-time workloads. And there are starting to be real-time > CPU-bound in-kernel workloads, and these must be handled without IPIing > the CPU, at least not in the common case. Therefore, this situation can > no longer be dismissed as an error case. Do explain. Doing "for (;;) ;" in a kernel RT thread is just as bad for general system health as is doing the same in userspace. Also, who runs his RT workload in-kernel ?