From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752109AbaANTJj (ORCPT ); Tue, 14 Jan 2014 14:09:39 -0500 Received: from g4t0014.houston.hp.com ([15.201.24.17]:40851 "EHLO g4t0014.houston.hp.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751610AbaANTJh (ORCPT ); Tue, 14 Jan 2014 14:09:37 -0500 Message-ID: <52D58B6A.5070103@hp.com> Date: Tue, 14 Jan 2014 14:09:30 -0500 From: Waiman Long User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:10.0.12) Gecko/20130109 Thunderbird/10.0.12 MIME-Version: 1.0 To: Richard Henderson CC: Matt Turner , Peter Zijlstra , Daniel J Blueman , "Paul E. McKenney" , Linux Kernel , Ivan Kokshaysky , Linus Torvalds Subject: Re: [PATCH v8 4/4] qrwlock: Use smp_store_release() in write_unlock() References: <52D353C8.4000000@numascale.com> <52D4172E.6030706@hp.com> <52D4A0C7.5070601@numascale.com> <20140114110307.GW7572@laptop.programming.kicks-ass.net> <52D57B60.9020209@twiddle.net> In-Reply-To: <52D57B60.9020209@twiddle.net> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 01/14/2014 01:01 PM, Richard Henderson wrote: > On 01/14/2014 09:08 AM, Matt Turner wrote: >> On Tue, Jan 14, 2014 at 3:03 AM, Peter Zijlstra wrote: >>> On Tue, Jan 14, 2014 at 10:28:23AM +0800, Daniel J Blueman wrote: >>>>> Peter, >>>>> >>>>> I found out that the build failure was caused by the fact that the >>>>> __native_word() macro (used internally by compiletime_assert_atomic()) >>>>> allows only a size of 4 or 8 for x86-64. The data type that I used is a >>>>> byte. Is there a reason why byte and short are not considered native? >>>> It seems likely it was implemented like that since there was no existing >>>> need; long can be relied on as the largest native type, so this should >>>> suffice and works here: >>> There's Alphas that cannot actually atomically adres a byte; I do not >>> konw if Linux cares about them, but if it does, we cannot in fact rely >>> on this in generic primitives like this. >> That's right, and thanks for the heads-up. Alpha can only address 4 >> and 8 bytes atomically. (LDL_L, LDQ_L, STL_C, STQ_C). >> >> The Byte-Word extension in EV56 doesn't add new atomics, so in fact no >> Alphas can address< 4 bytes atomically. >> > Emulated with aligned 4 byte atomics, and masking. The same is true for arm, > ppc, mips which, depending on cpu, also lack< 4 byte atomics. > I would like to know if the action of writing out a byte (e.g. *byte = 0) is atomic in those architectures or is emulated by a compiler-generated software read-modify-write. -Longman