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 E4E15C43381 for ; Sat, 2 Mar 2019 02:53:30 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id BC2592075B for ; Sat, 2 Mar 2019 02:53:30 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727858AbfCBCwb (ORCPT ); Fri, 1 Mar 2019 21:52:31 -0500 Received: from mga09.intel.com ([134.134.136.24]:61568 "EHLO mga09.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727337AbfCBCwa (ORCPT ); Fri, 1 Mar 2019 21:52:30 -0500 X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from fmsmga004.fm.intel.com ([10.253.24.48]) by orsmga102.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 01 Mar 2019 18:52:28 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.58,430,1544515200"; d="scan'208";a="148572589" Received: from romley-ivt3.sc.intel.com ([172.25.110.60]) by fmsmga004.fm.intel.com with ESMTP; 01 Mar 2019 18:52:27 -0800 From: Fenghua Yu To: "Thomas Gleixner" , "Ingo Molnar" , "Borislav Petkov" , "H Peter Anvin" , "Paolo Bonzini" , "Dave Hansen" , "Ashok Raj" , "Peter Zijlstra" , "Ravi V Shankar" , "Xiaoyao Li " Cc: "linux-kernel" , "x86" , kvm@vger.kernel.org, Fenghua Yu Subject: [PATCH v4 01/17] x86/common: Align cpu_caps_cleared and cpu_caps_set to unsigned long Date: Fri, 1 Mar 2019 18:44:55 -0800 Message-Id: <1551494711-213533-2-git-send-email-fenghua.yu@intel.com> X-Mailer: git-send-email 2.5.0 In-Reply-To: <1551494711-213533-1-git-send-email-fenghua.yu@intel.com> References: <1551494711-213533-1-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