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=-8.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=ham 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 2D89AC4332B for ; Fri, 20 Mar 2020 15:24:54 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id F2A892072D for ; Fri, 20 Mar 2020 15:24:53 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727581AbgCTPYx (ORCPT ); Fri, 20 Mar 2020 11:24:53 -0400 Received: from mx2.suse.de ([195.135.220.15]:56370 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726847AbgCTPYw (ORCPT ); Fri, 20 Mar 2020 11:24:52 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx2.suse.de (Postfix) with ESMTP id AAFFAAD68; Fri, 20 Mar 2020 15:24:50 +0000 (UTC) Subject: Re: [PATCH] bcache: optimize barrier usage for Rmw atomic bitops To: Davidlohr Bueso , kent.overstreet@gmail.com Cc: linux-bcache@vger.kernel.org, linux-kernel@vger.kernel.org, Davidlohr Bueso References: <20200129180802.24626-1-dave@stgolabs.net> From: Coly Li Organization: SUSE Labs Message-ID: <877a5349-3133-404a-86ea-02309080a520@suse.de> Date: Fri, 20 Mar 2020 23:24:45 +0800 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:68.0) Gecko/20100101 Thunderbird/68.5.0 MIME-Version: 1.0 In-Reply-To: <20200129180802.24626-1-dave@stgolabs.net> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2020/1/30 2:08 上午, Davidlohr Bueso wrote: > We can avoid the unnecessary barrier on non LL/SC architectures, > such as x86. Instead, use the smp_mb__after_atomic(). > Hi Davidlohr, > Signed-off-by: Davidlohr Bueso Sorry for replying late. Indeed we don't need to worry about the extra smp_mb() because the code patch gets called every 5 seconds by default, which is very infrequent. But I like this more accurate patch, it is in my testing already. And by your inspiration, I also fix some other locations to use smp_mb__before/after_atomic(). Thank you. Coly Li > --- > drivers/md/bcache/writeback.c | 6 +++--- > 1 file changed, 3 insertions(+), 3 deletions(-) > > diff --git a/drivers/md/bcache/writeback.c b/drivers/md/bcache/writeback.c > index 4a40f9eadeaf..284ff10f480f 100644 > --- a/drivers/md/bcache/writeback.c > +++ b/drivers/md/bcache/writeback.c > @@ -183,7 +183,7 @@ static void update_writeback_rate(struct work_struct *work) > */ > set_bit(BCACHE_DEV_RATE_DW_RUNNING, &dc->disk.flags); > /* paired with where BCACHE_DEV_RATE_DW_RUNNING is tested */ > - smp_mb(); > + smp_mb__after_atomic(); > > /* > * CACHE_SET_IO_DISABLE might be set via sysfs interface, > @@ -193,7 +193,7 @@ static void update_writeback_rate(struct work_struct *work) > test_bit(CACHE_SET_IO_DISABLE, &c->flags)) { > clear_bit(BCACHE_DEV_RATE_DW_RUNNING, &dc->disk.flags); > /* paired with where BCACHE_DEV_RATE_DW_RUNNING is tested */ > - smp_mb(); > + smp_mb__after_atomic(); > return; > } > > @@ -229,7 +229,7 @@ static void update_writeback_rate(struct work_struct *work) > */ > clear_bit(BCACHE_DEV_RATE_DW_RUNNING, &dc->disk.flags); > /* paired with where BCACHE_DEV_RATE_DW_RUNNING is tested */ > - smp_mb(); > + smp_mb__after_atomic(); > } > > static unsigned int writeback_delay(struct cached_dev *dc, > -- Coly Li