Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1762674AbdDSLfd (ORCPT ); Wed, 19 Apr 2017 07:35:33 -0400 Received: from merlin.infradead.org ([205.233.59.134]:54470 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1761254AbdDSLfa (ORCPT ); Wed, 19 Apr 2017 07:35:30 -0400 Date: Wed, 19 Apr 2017 13:35:12 +0200 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, marc.zyngier@arm.com Subject: Re: [PATCH v2 tip/core/rcu 0/13] Miscellaneous fixes for 4.12 Message-ID: <20170419113512.y6oyda43xh7wv3bd@hirez.programming.kicks-ass.net> References: <20170412165441.GA17149@linux.vnet.ibm.com> <20170417232714.GA19013@linux.vnet.ibm.com> <20170419112845.3rt3zlyzuzert647@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170419112845.3rt3zlyzuzert647@hirez.programming.kicks-ass.net> User-Agent: NeoMutt/20170113 (1.7.2) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 543 Lines: 14 On Wed, Apr 19, 2017 at 01:28:45PM +0200, Peter Zijlstra wrote: > > So the thing Maz complained about is because KVM assumes > synchronize_srcu() is 'free' when there is no srcu_read_lock() activity. > This series 'breaks' that. Could've been call_srcu() instead. Looking at the code that triggers the sp->running case and we slow down. That is !running will queue and insta-complete the callback, resulting in done=true and no waiting. > > I've not looked hard enough at the new SRCU to see if its possible to > re-instate that feature.