Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752001AbaASIER (ORCPT ); Sun, 19 Jan 2014 03:04:17 -0500 Received: from e35.co.us.ibm.com ([32.97.110.153]:34366 "EHLO e35.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750774AbaASIEP (ORCPT ); Sun, 19 Jan 2014 03:04:15 -0500 Date: Sun, 19 Jan 2014 00:04:05 -0800 From: "Paul E. McKenney" To: Linus Torvalds Cc: Peter Zijlstra , Matt Turner , Waiman Long , Linux Kernel , Ivan Kokshaysky , Daniel J Blueman , Richard Henderson Subject: Re: [PATCH v8 4/4] qrwlock: Use smp_store_release() in write_unlock() Message-ID: <20140119080405.GB10038@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <20140115205346.GF10038@linux.vnet.ibm.com> <20140115232134.GM31570@twins.programming.kicks-ass.net> <20140116103659.GO7572@laptop.programming.kicks-ass.net> <20140118100105.GV10038@linux.vnet.ibm.com> <20140118113406.GY30183@twins.programming.kicks-ass.net> <20140118122548.GX10038@linux.vnet.ibm.com> <20140118124136.GZ30183@twins.programming.kicks-ass.net> <20140118212227.GA10038@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 14011908-6688-0000-0000-000005AE1A2A Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, Jan 18, 2014 at 04:57:05PM -0800, Linus Torvalds wrote: > On Sat, Jan 18, 2014 at 1:22 PM, Paul E. McKenney > wrote: > > > > Yes, this requires that -all- updates to the fields in the machine word > > in question use atomic rmw. Which would not be pretty from a core-code > > perspective. Hence my suggestion of ceasing Linux-kernel support for > > DEC Alpha CPUs that don't support byte operations. Also need 16-bit > > operations as well, of course... > > I'm not seeing this. > > Why the hell would you have byte- or halfword-sized versions of the > store_release or load_acquire things on alpha anyway? > > What it means is that data structures that do locking or atomics need > to be "int" or "long" on alpha. That has always been true. What do > you claim has changed? OK, another approach would be to never add "select ARCH_USE_QUEUE_RWLOCK" on Alpha, at least if the queued rwlocks really do want to atomically manipulate bytes. After all, the Alpha systems that I know about don't have enough CPUs to make queued rwlocks necessary anyway. Much simpler solution! Is this what you were getting at, or am I missing your point? Thanx, Paul -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/