From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-5.5 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id B3C2EC4727E for ; Wed, 30 Sep 2020 12:48:53 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 71DC7207FB for ; Wed, 30 Sep 2020 12:48:53 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729693AbgI3Msx (ORCPT ); Wed, 30 Sep 2020 08:48:53 -0400 Received: from elvis.franken.de ([193.175.24.41]:36177 "EHLO elvis.franken.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725776AbgI3Msw (ORCPT ); Wed, 30 Sep 2020 08:48:52 -0400 Received: from uucp (helo=alpha) by elvis.franken.de with local-bsmtp (Exim 3.36 #1) id 1kNbXO-0003um-00; Wed, 30 Sep 2020 14:48:50 +0200 Received: by alpha.franken.de (Postfix, from userid 1000) id E9CE4C103C; Wed, 30 Sep 2020 13:16:44 +0200 (CEST) Date: Wed, 30 Sep 2020 13:16:44 +0200 From: Thomas Bogendoerfer To: Heiher Cc: linux-mips@vger.kernel.org, Jiaxun Yang , Huacai Chen , Paul Burton , "Maciej W . Rozycki" Subject: Re: [PATCH] MIPS: Optional SYNC emulation Message-ID: <20200930111644.GA19903@alpha.franken.de> References: <20200821031228.31231-1-r@hev.cc> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200821031228.31231-1-r@hev.cc> User-Agent: Mutt/1.5.23 (2014-03-12) Precedence: bulk List-ID: X-Mailing-List: linux-mips@vger.kernel.org On Fri, Aug 21, 2020 at 11:12:28AM +0800, Heiher wrote: > MIPS ISA defines several types of memory barrier, of which Type-0 (full barrier) > is required, and the others are optional. In some vendor implementation (such as > Loongson), all optional parts are implemented to emit an illegal instruction > exception. Here, emulate to full barrier to ensure the functional semantics. > > If an implementation does not support SYNC 0, it should also not support SMP, so > the `smp_mb()` is only a compilation barrier. I see your point, but isn't taking an exception already more than a compiler barrier ? Does the missing sync hurt in real life ? Thomas. -- Crap can work. Given enough thrust pigs will fly, but it's not necessarily a good idea. [ RFC1925, 2.3 ]