From patchwork Thu Oct 20 15:51:04 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Uros Bizjak X-Patchwork-Id: 13013697 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 EDDFEC4332F for ; Thu, 20 Oct 2022 15:51:27 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230322AbiJTPv1 (ORCPT ); Thu, 20 Oct 2022 11:51:27 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:33826 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230406AbiJTPvX (ORCPT ); Thu, 20 Oct 2022 11:51:23 -0400 Received: from mail-wm1-x334.google.com (mail-wm1-x334.google.com [IPv6:2a00:1450:4864:20::334]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 396821B90FE; Thu, 20 Oct 2022 08:51:16 -0700 (PDT) Received: by mail-wm1-x334.google.com with SMTP id 186-20020a1c02c3000000b003c6c154d528so2685621wmc.4; Thu, 20 Oct 2022 08:51:16 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; h=content-transfer-encoding:mime-version:message-id:date:subject:cc :to:from:from:to:cc:subject:date:message-id:reply-to; bh=54fd/0yen88eFOEGtvTo0HIRTRehsPlXZmjj7D9lRYM=; b=AYzEUOOvgKrh8OY79DYRWSgwx6N8g/vR6J3zOIQt1gL8WOjDLWAvK0msuxAhyjy8H5 gggcBJuxspkS1/wgrQLT9gieS4kFqu/mJAgZ91Qbp9fsYRwVSSdVjymrhQOpRcfHFyrs vNRr0nHhoAQ+F8gPsOe5wA8m7xO+PAeHiFT3p0gr84lf5L/rtvXxecm4lkmf8I+c2Toh 2iNtwXaKtllOhvTEnCy8jnkFj3p8ozL9gV+oeNG/AXBMdhpeiy36hxivHZN0IEx6e6Fw 5Fpi5LiZdrRHQMMbr9nRKNAjvE+yYYa1ZFS3CvKJEAZ++wOhbYVd2+1kidN34KTWWFyZ FD0w== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=content-transfer-encoding:mime-version:message-id:date:subject:cc :to:from:x-gm-message-state:from:to:cc:subject:date:message-id :reply-to; bh=54fd/0yen88eFOEGtvTo0HIRTRehsPlXZmjj7D9lRYM=; b=bFpCd6txKIsCYOdo9RQx292AGuDTLgwWP7IldpdxKjB8BgE/V2a82KeXcQ5mvU7eoA SrNjf258FHSYw5g/oKffjx/3bohbnsTSWFL4etuJyntjhmMCfTkmXWek7QWpAnlm9qeq ihtFzT8u858xCqI2+VMgyBMVVlnAeeMxNsGqFO5+YfxbQ7kukMOi2eW1CMms8yYqWy2C 98o8Qx8YJzLVlsTnbTt/QXuLkqoYeO5/Gp9QeXh9GYW/g3LPGCLvONmWE7UU0vh5vQDY DjvQnHvCTHwunKKlsTwcPIs6sDKzUdrZUe6E0YAmOl5XJ6Np7z4Ljn4Zn4VQCL1iuYp4 2EUw== X-Gm-Message-State: ACrzQf3jQhfsei/+jAHvASx6INqiaz7SRou86Y6u9AeN2P+pkGGKDZXT 5WGHSMWBrhv/3O4ezgn/O2q90TGUDt+xUA== X-Google-Smtp-Source: AMsMyM4kwoM78oquyzfzXtDeD8DlaN+JrS1iv5KYcCC4O7CgALTGucAn/e7/srb06hAYQjUkLMB/vQ== X-Received: by 2002:a1c:f60d:0:b0:3be:708b:c96c with SMTP id w13-20020a1cf60d000000b003be708bc96cmr31458957wmc.168.1666281074889; Thu, 20 Oct 2022 08:51:14 -0700 (PDT) Received: from localhost.localdomain ([46.248.82.114]) by smtp.gmail.com with ESMTPSA id b21-20020a05600c4e1500b003a83ca67f73sm31645wmq.3.2022.10.20.08.51.14 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 20 Oct 2022 08:51:14 -0700 (PDT) From: Uros Bizjak To: linux-raid@vger.kernel.org, linux-kernel@vger.kernel.org Cc: Uros Bizjak , Song Liu Subject: [PATCH v2] raid5-cache: use try_cmpxchg in r5l_wake_reclaim Date: Thu, 20 Oct 2022 17:51:04 +0200 Message-Id: <20221020155104.9485-1-ubizjak@gmail.com> X-Mailer: git-send-email 2.37.3 MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-raid@vger.kernel.org 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 --- 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); }