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=-11.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS 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 44D59C47409 for ; Fri, 17 Jan 2020 10:09:21 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 272E32469A for ; Fri, 17 Jan 2020 10:09:21 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729300AbgAQKJU (ORCPT ); Fri, 17 Jan 2020 05:09:20 -0500 Received: from Galois.linutronix.de ([193.142.43.55]:55438 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729208AbgAQKJQ (ORCPT ); Fri, 17 Jan 2020 05:09:16 -0500 Received: from [5.158.153.53] (helo=tip-bot2.lab.linutronix.de) by Galois.linutronix.de with esmtpsa (TLS1.2:DHE_RSA_AES_256_CBC_SHA256:256) (Exim 4.80) (envelope-from ) id 1isOYv-0005ay-OB; Fri, 17 Jan 2020 11:09:09 +0100 Received: from [127.0.1.1] (localhost [IPv6:::1]) by tip-bot2.lab.linutronix.de (Postfix) with ESMTP id 6994C1C0330; Fri, 17 Jan 2020 11:09:09 +0100 (CET) Date: Fri, 17 Jan 2020 10:09:09 -0000 From: "tip-bot2 for Waiman Long" Reply-to: linux-kernel@vger.kernel.org To: linux-tip-commits@vger.kernel.org Subject: [tip: locking/core] locking/osq: Use optimized spinning loop for arm64 Cc: Waiman Long , "Peter Zijlstra (Intel)" , Will Deacon , x86 , LKML In-Reply-To: <20200113150735.21956-1-longman@redhat.com> References: <20200113150735.21956-1-longman@redhat.com> MIME-Version: 1.0 Message-ID: <157925574923.396.5221009397252239087.tip-bot2@tip-bot2> X-Mailer: tip-git-log-daemon Robot-ID: Robot-Unsubscribe: Contact to get blacklisted from these emails Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit X-Linutronix-Spam-Score: -1.0 X-Linutronix-Spam-Level: - X-Linutronix-Spam-Status: No , -1.0 points, 5.0 required, ALL_TRUSTED=-1,SHORTCIRCUIT=-0.0001 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The following commit has been merged into the locking/core branch of tip: Commit-ID: f5bfdc8e3947a7ae489cf8ae9cfd6b3fb357b952 Gitweb: https://git.kernel.org/tip/f5bfdc8e3947a7ae489cf8ae9cfd6b3fb357b952 Author: Waiman Long AuthorDate: Mon, 13 Jan 2020 10:07:35 -05:00 Committer: Peter Zijlstra CommitterDate: Fri, 17 Jan 2020 10:19:30 +01:00 locking/osq: Use optimized spinning loop for arm64 Arm64 has a more optimized spinning loop (atomic_cond_read_acquire) using wfe for spinlock that can boost performance of sibling threads by putting the current cpu to a wait state that is broken only when the monitored variable changes or an external event happens. OSQ has a more complicated spinning loop. Besides the lock value, it also checks for need_resched() and vcpu_is_preempted(). The check for need_resched() is not a problem as it is only set by the tick interrupt handler. That will be detected by the spinning cpu right after iret. The vcpu_is_preempted() check, however, is a problem as changes to the preempt state of of previous node will not affect the wait state. For ARM64, vcpu_is_preempted is not currently defined and so is a no-op. Will has indicated that he is planning to para-virtualize wfe instead of defining vcpu_is_preempted for PV support. So just add a comment in arch/arm64/include/asm/spinlock.h to indicate that vcpu_is_preempted() should not be defined as suggested. On a 2-socket 56-core 224-thread ARM64 system, a kernel mutex locking microbenchmark was run for 10s with and without the patch. The performance numbers before patch were: Running locktest with mutex [runtime = 10s, load = 1] Threads = 224, Min/Mean/Max = 316/123,143/2,121,269 Threads = 224, Total Rate = 2,757 kop/s; Percpu Rate = 12 kop/s After patch, the numbers were: Running locktest with mutex [runtime = 10s, load = 1] Threads = 224, Min/Mean/Max = 334/147,836/1,304,787 Threads = 224, Total Rate = 3,311 kop/s; Percpu Rate = 15 kop/s So there was about 20% performance improvement. Signed-off-by: Waiman Long Signed-off-by: Peter Zijlstra (Intel) Acked-by: Will Deacon Link: https://lkml.kernel.org/r/20200113150735.21956-1-longman@redhat.com --- arch/arm64/include/asm/spinlock.h | 9 +++++++++ kernel/locking/osq_lock.c | 23 ++++++++++------------- 2 files changed, 19 insertions(+), 13 deletions(-) diff --git a/arch/arm64/include/asm/spinlock.h b/arch/arm64/include/asm/spinlock.h index b093b28..102404d 100644 --- a/arch/arm64/include/asm/spinlock.h +++ b/arch/arm64/include/asm/spinlock.h @@ -11,4 +11,13 @@ /* See include/linux/spinlock.h */ #define smp_mb__after_spinlock() smp_mb() +/* + * Changing this will break osq_lock() thanks to the call inside + * smp_cond_load_relaxed(). + * + * See: + * https://lore.kernel.org/lkml/20200110100612.GC2827@hirez.programming.kicks-ass.net + */ +#define vcpu_is_preempted(cpu) false + #endif /* __ASM_SPINLOCK_H */ diff --git a/kernel/locking/osq_lock.c b/kernel/locking/osq_lock.c index 6ef600a..1f77349 100644 --- a/kernel/locking/osq_lock.c +++ b/kernel/locking/osq_lock.c @@ -134,20 +134,17 @@ bool osq_lock(struct optimistic_spin_queue *lock) * cmpxchg in an attempt to undo our queueing. */ - while (!READ_ONCE(node->locked)) { - /* - * If we need to reschedule bail... so we can block. - * Use vcpu_is_preempted() to avoid waiting for a preempted - * lock holder: - */ - if (need_resched() || vcpu_is_preempted(node_cpu(node->prev))) - goto unqueue; - - cpu_relax(); - } - return true; + /* + * Wait to acquire the lock or cancelation. Note that need_resched() + * will come with an IPI, which will wake smp_cond_load_relaxed() if it + * is implemented with a monitor-wait. vcpu_is_preempted() relies on + * polling, be careful. + */ + if (smp_cond_load_relaxed(&node->locked, VAL || need_resched() || + vcpu_is_preempted(node_cpu(node->prev)))) + return true; -unqueue: + /* unqueue */ /* * Step - A -- stabilize @prev *