From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752773AbdLEWJu (ORCPT ); Tue, 5 Dec 2017 17:09:50 -0500 Received: from mx1.redhat.com ([209.132.183.28]:58060 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752145AbdLEWJl (ORCPT ); Tue, 5 Dec 2017 17:09:41 -0500 Date: Wed, 6 Dec 2017 00:09:36 +0200 From: "Michael S. Tsirkin" To: Peter Zijlstra Cc: "Paul E. McKenney" , 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, fweisbec@gmail.com, oleg@redhat.com, Jason Wang , kvm@vger.kernel.org, virtualization@lists.linux-foundation.org, netdev@vger.kernel.org Subject: Re: [PATCH tip/core/rcu 21/21] drivers/vhost: Remove now-redundant read_barrier_depends() Message-ID: <20171206000541-mutt-send-email-mst@kernel.org> References: <20171205202928-mutt-send-email-mst@kernel.org> <20171205183946.GP3165@worktop.lehotels.local> <20171205204928-mutt-send-email-mst@kernel.org> <20171205191733.GQ3165@worktop.lehotels.local> <20171205212053-mutt-send-email-mst@kernel.org> <20171205193339.GP7829@linux.vnet.ibm.com> <20171205215020-mutt-send-email-mst@kernel.org> <20171205200801.GR7829@linux.vnet.ibm.com> <20171205222857-mutt-send-email-mst@kernel.org> <20171205215700.GV3165@worktop.lehotels.local> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20171205215700.GV3165@worktop.lehotels.local> X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.32]); Tue, 05 Dec 2017 22:09:41 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Dec 05, 2017 at 10:57:00PM +0100, Peter Zijlstra wrote: > On Tue, Dec 05, 2017 at 11:24:49PM +0200, Michael S. Tsirkin wrote: > > READ_ONCE is really all over the place (some code literally replaced all > > memory accesses with READ/WRITE ONCE). > > Yeah, so? Oh my point was I can't just look for READ_ONCE and go *that's the pair*. there are too many of these. At Paul's suggestion I will document the pairing *this read once has a barrier that is paired with that barrier*. > Complain to the compiler people for forcing us into that. In some cases when you end up with all accesses going through read/write once volatile just might better. > > Would an API like WRITE_POINTER()/smp_store_pointer make sense, > > and READ_POINTER for symmetry? > > No, the whole point of the exercise was to get away from the fact that > dependent loads are special. It's a pity that dependent stores are still special. -- MST