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=-9.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,URIBL_BLOCKED, USER_AGENT_GIT 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 1ED67C282DA for ; Sat, 2 Feb 2019 05:21:59 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id E37A02086C for ; Sat, 2 Feb 2019 05:21:58 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727046AbfBBFVT (ORCPT ); Sat, 2 Feb 2019 00:21:19 -0500 Received: from mga12.intel.com ([192.55.52.136]:23419 "EHLO mga12.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726516AbfBBFVS (ORCPT ); Sat, 2 Feb 2019 00:21:18 -0500 X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga004.jf.intel.com ([10.7.209.38]) by fmsmga106.fm.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 01 Feb 2019 21:21:17 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.56,551,1539673200"; d="scan'208";a="271934471" Received: from romley-ivt3.sc.intel.com ([172.25.110.60]) by orsmga004.jf.intel.com with ESMTP; 01 Feb 2019 21:21:16 -0800 From: Fenghua Yu To: "Thomas Gleixner" , "Ingo Molnar" , "H Peter Anvin" , "Dave Hansen" , "Ashok Raj" , "Peter Zijlstra" , "Michael Chan" , "Ravi V Shankar" , "Ricardo Neri" Cc: "linux-kernel" , "x86" , Fenghua Yu Subject: [PATCH v3 01/10] x86/common: Align cpu_caps_cleared and cpu_caps_set to unsigned long Date: Fri, 1 Feb 2019 21:14:42 -0800 Message-Id: <1549084491-57808-2-git-send-email-fenghua.yu@intel.com> X-Mailer: git-send-email 2.5.0 In-Reply-To: <1549084491-57808-1-git-send-email-fenghua.yu@intel.com> References: <1549084491-57808-1-git-send-email-fenghua.yu@intel.com> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org cpu_caps_cleared and cpu_caps_set may not be aligned to unsigned long. Atomic operations (i.e. set_bit and clear_bit) on the bitmaps may access two cache lines (a.k.a. split lock) and lock bus to block all memory accesses from other processors to ensure atomicity. To avoid the overall performance degradation from the bus locking, align the two variables to unsigned long. Defining the variables as unsigned long may also fix the issue because they are naturally aligned to unsigned long. But that needs additional code changes. Adding __aligned(unsigned long) are simpler fixes. Signed-off-by: Fenghua Yu --- arch/x86/kernel/cpu/common.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c index cb28e98a0659..51ab37ba5f64 100644 --- a/arch/x86/kernel/cpu/common.c +++ b/arch/x86/kernel/cpu/common.c @@ -488,8 +488,9 @@ static const char *table_lookup_model(struct cpuinfo_x86 *c) return NULL; /* Not found */ } -__u32 cpu_caps_cleared[NCAPINTS + NBUGINTS]; -__u32 cpu_caps_set[NCAPINTS + NBUGINTS]; +/* Unsigned long alignment to avoid split lock in atomic bitmap ops */ +__u32 cpu_caps_cleared[NCAPINTS + NBUGINTS] __aligned(sizeof(unsigned long)); +__u32 cpu_caps_set[NCAPINTS + NBUGINTS] __aligned(sizeof(unsigned long)); void load_percpu_segment(int cpu) { -- 2.7.4