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=-9.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,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 141D9ECDE44 for ; Wed, 31 Oct 2018 23:08:02 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id D027D2064C for ; Wed, 31 Oct 2018 23:08:01 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="cqV2sVlU" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org D027D2064C Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729499AbeKAIIK (ORCPT ); Thu, 1 Nov 2018 04:08:10 -0400 Received: from mail.kernel.org ([198.145.29.99]:56690 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729434AbeKAIIJ (ORCPT ); Thu, 1 Nov 2018 04:08:09 -0400 Received: from sasha-vm.mshome.net (c-73-47-72-35.hsd1.nh.comcast.net [73.47.72.35]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 33F2E20664; Wed, 31 Oct 2018 23:07:57 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1541027278; bh=bRKgJ+xBYUCEpjXEyHI+O3QUHYNbv1I4xyLFczcsd4g=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=cqV2sVlUvuxbd6FVksxhyTlUQlnPFTumaZf1RlZgqCoAzq/L7NdtvNFV1cDB1Ha1g mjcgZaafyGr338U/lFRJlTUKqfJcbRgcA7oKakPpohonUw4Bhj1g5lEaY8lSHcrgOZ zWOhUz9qlb5xar0Tn+pMlQTgJmRn+49JxZy/OiKo= From: Sasha Levin To: stable@vger.kernel.org, linux-kernel@vger.kernel.org Cc: Waiman Long , Andrew Morton , Linus Torvalds , "Paul E . McKenney" , Peter Zijlstra , Thomas Gleixner , Will Deacon , Ingo Molnar , Sasha Levin Subject: [PATCH AUTOSEL 4.18 003/126] locking/lockdep: Fix debug_locks off performance problem Date: Wed, 31 Oct 2018 19:05:51 -0400 Message-Id: <20181031230754.29029-3-sashal@kernel.org> X-Mailer: git-send-email 2.17.1 In-Reply-To: <20181031230754.29029-1-sashal@kernel.org> References: <20181031230754.29029-1-sashal@kernel.org> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Waiman Long [ Upstream commit 9506a7425b094d2f1d9c877ed5a78f416669269b ] It was found that when debug_locks was turned off because of a problem found by the lockdep code, the system performance could drop quite significantly when the lock_stat code was also configured into the kernel. For instance, parallel kernel build time on a 4-socket x86-64 server nearly doubled. Further analysis into the cause of the slowdown traced back to the frequent call to debug_locks_off() from the __lock_acquired() function probably due to some inconsistent lockdep states with debug_locks off. The debug_locks_off() function did an unconditional atomic xchg to write a 0 value into debug_locks which had already been set to 0. This led to severe cacheline contention in the cacheline that held debug_locks. As debug_locks is being referenced in quite a few different places in the kernel, this greatly slow down the system performance. To prevent that trashing of debug_locks cacheline, lock_acquired() and lock_contended() now checks the state of debug_locks before proceeding. The debug_locks_off() function is also modified to check debug_locks before calling __debug_locks_off(). Signed-off-by: Waiman Long Cc: Andrew Morton Cc: Linus Torvalds Cc: Paul E. McKenney Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: Will Deacon Link: http://lkml.kernel.org/r/1539913518-15598-1-git-send-email-longman@redhat.com Signed-off-by: Ingo Molnar Signed-off-by: Sasha Levin --- kernel/locking/lockdep.c | 4 ++-- lib/debug_locks.c | 2 +- 2 files changed, 3 insertions(+), 3 deletions(-) diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c index 5fa4d3138bf1..aa6ebb799f16 100644 --- a/kernel/locking/lockdep.c +++ b/kernel/locking/lockdep.c @@ -4148,7 +4148,7 @@ void lock_contended(struct lockdep_map *lock, unsigned long ip) { unsigned long flags; - if (unlikely(!lock_stat)) + if (unlikely(!lock_stat || !debug_locks)) return; if (unlikely(current->lockdep_recursion)) @@ -4168,7 +4168,7 @@ void lock_acquired(struct lockdep_map *lock, unsigned long ip) { unsigned long flags; - if (unlikely(!lock_stat)) + if (unlikely(!lock_stat || !debug_locks)) return; if (unlikely(current->lockdep_recursion)) diff --git a/lib/debug_locks.c b/lib/debug_locks.c index 96c4c633d95e..124fdf238b3d 100644 --- a/lib/debug_locks.c +++ b/lib/debug_locks.c @@ -37,7 +37,7 @@ EXPORT_SYMBOL_GPL(debug_locks_silent); */ int debug_locks_off(void) { - if (__debug_locks_off()) { + if (debug_locks && __debug_locks_off()) { if (!debug_locks_silent) { console_verbose(); return 1; -- 2.17.1