From nobody Fri Jun 19 15:47:15 2026 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 0C56FC433EF for ; Sat, 2 Apr 2022 03:08:51 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231800AbiDBDKj (ORCPT ); Fri, 1 Apr 2022 23:10:39 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:46442 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1348321AbiDBDKX (ORCPT ); Fri, 1 Apr 2022 23:10:23 -0400 Received: from out30-57.freemail.mail.aliyun.com (out30-57.freemail.mail.aliyun.com [115.124.30.57]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id CFACBCC4 for ; Fri, 1 Apr 2022 20:08:27 -0700 (PDT) X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R211e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=e01e04407;MF=dtcccc@linux.alibaba.com;NM=1;PH=DS;RN=9;SR=0;TI=SMTPD_---0V8xeb44_1648868903; Received: from localhost.localdomain(mailfrom:dtcccc@linux.alibaba.com fp:SMTPD_---0V8xeb44_1648868903) by smtp.aliyun-inc.com(127.0.0.1); Sat, 02 Apr 2022 11:08:24 +0800 From: Tianchen Ding To: Andrew Morton , Thomas Gleixner , Fenghua Yu , Borislav Petkov , Pavel Tatashin , NeilBrown , Vasily Averin , "Matthew Wilcox (Oracle)" Cc: linux-kernel@vger.kernel.org Subject: [RFC PATCH] sched: avoid unnecessary atomic_read when sync_core_before_usermode() is empty Date: Sat, 2 Apr 2022 11:08:22 +0800 Message-Id: <20220402030822.11441-1-dtcccc@linux.alibaba.com> X-Mailer: git-send-email 2.30.1 (Apple Git-130) MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" On archs except x86, CONFIG_ARCH_HAS_SYNC_CORE_BEFORE_USERMODE is not defined. We found membarrier_mm_sync_core_before_usermode() looks like this when compiled by gcc10: if (current->mm !=3D mm) return; atomic_read(&mm->membarrier_state); This memory access is unnecessary. Remove it to improve performance. Signed-off-by: Tianchen Ding --- include/linux/sched/mm.h | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/include/linux/sched/mm.h b/include/linux/sched/mm.h index a80356e9dc69..3ded68d9f913 100644 --- a/include/linux/sched/mm.h +++ b/include/linux/sched/mm.h @@ -401,6 +401,7 @@ enum { #include #endif =20 +#ifdef CONFIG_ARCH_HAS_SYNC_CORE_BEFORE_USERMODE static inline void membarrier_mm_sync_core_before_usermode(struct mm_struc= t *mm) { if (current->mm !=3D mm) @@ -410,6 +411,11 @@ static inline void membarrier_mm_sync_core_before_user= mode(struct mm_struct *mm) return; sync_core_before_usermode(); } +#else +static inline void membarrier_mm_sync_core_before_usermode(struct mm_struc= t *mm) +{ +} +#endif =20 extern void membarrier_exec_mmap(struct mm_struct *mm); =20 --=20 2.33.0