From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753545AbaFMQVq (ORCPT ); Fri, 13 Jun 2014 12:21:46 -0400 Received: from mail-wg0-f42.google.com ([74.125.82.42]:36699 "EHLO mail-wg0-f42.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752978AbaFMQVf (ORCPT ); Fri, 13 Jun 2014 12:21:35 -0400 Date: Fri, 13 Jun 2014 18:21:32 +0200 From: Frederic Weisbecker To: "Paul E. McKenney" Cc: LKML , Josh Triplett , Steven Rostedt , Mathieu Desnoyers Subject: Re: [PATCH] rcu: Only pin GP kthread when full dynticks is actually used Message-ID: <20140613162130.GP6635@localhost.localdomain> References: <1402618619-32630-1-git-send-email-fweisbec@gmail.com> <20140613012432.GH4581@linux.vnet.ibm.com> <20140613013515.GA9589@linux.vnet.ibm.com> <20140613124714.GC6635@localhost.localdomain> <20140613155233.GM4581@linux.vnet.ibm.com> <20140613160002.GL6635@localhost.localdomain> <20140613161630.GQ4581@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20140613161630.GQ4581@linux.vnet.ibm.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Jun 13, 2014 at 09:16:30AM -0700, Paul E. McKenney wrote: > > Is it because we have dynticks CPUs staying too long in the kernel without > > taking any quiescent states? Are we perhaps missing some rcu_user_enter() or > > things? > > Sort of the former, but combined with the fact that in-kernel CPUs still > need scheduling-clock interrupts for RCU to make progress. I could > move this to RCU's context-switch hook, but that could be very bad for > workloads that do lots of context switching. Or I can restart the tick if the CPU stays in the kernel for too long without a tick. I think that's what we were doing before but we removed that because we never implemented it correctly (we sent scheduler IPI that did nothing...)