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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 3DED3C433FE for ; Thu, 20 Oct 2022 18:10:53 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230190AbiJTSKv (ORCPT ); Thu, 20 Oct 2022 14:10:51 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:42078 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230090AbiJTSKt (ORCPT ); Thu, 20 Oct 2022 14:10:49 -0400 Received: from ams.source.kernel.org (ams.source.kernel.org [145.40.68.75]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id AB71A16F74E; Thu, 20 Oct 2022 11:10:35 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id 90483B8274A; Thu, 20 Oct 2022 18:09:40 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 4CA72C433D7; Thu, 20 Oct 2022 18:09:39 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1666289379; bh=PBunTa7rce9oPUHewe2pTnhit7GvQJqymuWwU3QKUXM=; h=References:In-Reply-To:From:Date:Subject:To:Cc:From; b=T6KODpSujSMwgSBYn8ps6OsFiGEP+mFua+xq2LF7eTAmVCFXap2zrS/xQskdZRnE3 sX6muDQriwpDR8ycL/2J8aoBIPcJnM5F8FT3aZD2wmh0qRgH8TE2NhYpZ8XQowTc4R AFilFdujps4dudONDLufhK52DdFGHp5Kse+jkrtu1+fhYLGsoLLo9o3B3NUfXN39cj bp65K+KJzSANN87wy8wz/IDYYuG2lN3Isu/JdpCHHbkAaYIngamdyqJiUsz+kRsyWi 0spb8hQKhsmznSY1j0NmKbNbcm9+G2EkHxv5sW5r8cvyfB8i6yuaQq0ADtV1rx1hKj ePH7bGJEhpV6Q== Received: by mail-ej1-f48.google.com with SMTP id a26so1465070ejc.4; Thu, 20 Oct 2022 11:09:39 -0700 (PDT) X-Gm-Message-State: ACrzQf3g+BfHcZ9ADJSVA4HOcQcdAMBNAar4ttqM6haFPZQnlCgjPmxh tvpX5g6Txwm+6FnscNco6iImT/ms//bGSK9yaiA= X-Google-Smtp-Source: AMsMyM6dBHethUPJpGWt/pGXdbIIfVcM3sIT6J9dz+n7IuFyddVg1deCn3XF+9udYMoHeEpl4tupoWZ4gVhAZEyiJik= X-Received: by 2002:a17:906:eec1:b0:782:6384:76be with SMTP id wu1-20020a170906eec100b00782638476bemr12134290ejb.756.1666289377447; Thu, 20 Oct 2022 11:09:37 -0700 (PDT) MIME-Version: 1.0 References: <20221020155104.9485-1-ubizjak@gmail.com> In-Reply-To: <20221020155104.9485-1-ubizjak@gmail.com> From: Song Liu Date: Thu, 20 Oct 2022 11:09:25 -0700 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH v2] raid5-cache: use try_cmpxchg in r5l_wake_reclaim To: Uros Bizjak Cc: linux-raid@vger.kernel.org, linux-kernel@vger.kernel.org Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-raid@vger.kernel.org On Thu, Oct 20, 2022 at 8:51 AM Uros Bizjak wrote: > > Use try_cmpxchg instead of cmpxchg (*ptr, old, new) == old in > r5l_wake_reclaim. 86 CMPXCHG instruction returns success in ZF flag, so > this change saves a compare after cmpxchg (and related move instruction in > front of cmpxchg). > > Also, try_cmpxchg implicitly assigns old *ptr value to "old" when cmpxchg > fails. There is no need to re-read the value in the loop. > > Note that the value from *ptr should be read using READ_ONCE to prevent > the compiler from merging, refetching or reordering the read. > > No functional change intended. > > Cc: Song Liu > Signed-off-by: Uros Bizjak Applied to md-next. Thanks! Song > --- > v2: Fix garbled subject line > --- > drivers/md/raid5-cache.c | 5 +++-- > 1 file changed, 3 insertions(+), 2 deletions(-) > > diff --git a/drivers/md/raid5-cache.c b/drivers/md/raid5-cache.c > index 832d8566e165..a63023aae21e 100644 > --- a/drivers/md/raid5-cache.c > +++ b/drivers/md/raid5-cache.c > @@ -1565,11 +1565,12 @@ void r5l_wake_reclaim(struct r5l_log *log, sector_t space) > > if (!log) > return; > + > + target = READ_ONCE(log->reclaim_target); > do { > - target = log->reclaim_target; > if (new < target) > return; > - } while (cmpxchg(&log->reclaim_target, target, new) != target); > + } while (!try_cmpxchg(&log->reclaim_target, &target, new)); > md_wakeup_thread(log->reclaim_thread); > } > > -- > 2.37.3 >