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=-6.9 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,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 DA75FC33CAD for ; Mon, 13 Jan 2020 15:07:54 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id ADD1C207E0 for ; Mon, 13 Jan 2020 15:07:54 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="HU2qf7r1" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728873AbgAMPHy (ORCPT ); Mon, 13 Jan 2020 10:07:54 -0500 Received: from us-smtp-delivery-1.mimecast.com ([205.139.110.120]:22119 "EHLO us-smtp-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726399AbgAMPHx (ORCPT ); Mon, 13 Jan 2020 10:07:53 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1578928071; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc; bh=j0msucI64dJuIAu2X81lzy2WWfJxmhNNupBdmcu4cNw=; b=HU2qf7r1aTUusC0blwg/6Dccy8RQS+tAHq2M+ESE8qU1ASSi/sK4EQULJYB5Abhe5nV30y 4M6OY/61xFOpkmC4g0a1E/q4zHVx2Z+axgX+ChhY2TjqWX+1GMuF36i+1KzhA3mDaIzvTq mZn/7AF+XE17tj2XoMVWL6HzGaEA4lc= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-228-17KnZeizOzqCtpqsnADSdg-1; Mon, 13 Jan 2020 10:07:48 -0500 X-MC-Unique: 17KnZeizOzqCtpqsnADSdg-1 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id BF5A210054E3; Mon, 13 Jan 2020 15:07:46 +0000 (UTC) Received: from llong.com (dhcp-17-59.bos.redhat.com [10.18.17.59]) by smtp.corp.redhat.com (Postfix) with ESMTP id 325425C21B; Mon, 13 Jan 2020 15:07:43 +0000 (UTC) From: Waiman Long To: Peter Zijlstra , Ingo Molnar , Will Deacon , Catalin Marinas Cc: linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, maz@kernel.org, yezengruan , Waiman Long Subject: [PATCH v3] locking/osq: Use optimized spinning loop for arm64 Date: Mon, 13 Jan 2020 10:07:35 -0500 Message-Id: <20200113150735.21956-1-longman@redhat.com> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 --- arch/arm64/include/asm/spinlock.h | 9 +++++++++ kernel/locking/osq_lock.c | 17 ++++------------- 2 files changed, 13 insertions(+), 13 deletions(-) diff --git a/arch/arm64/include/asm/spinlock.h b/arch/arm64/include/asm/spinlock.h index b093b287babf..102404dc1e13 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 6ef600aa0f47..e42893f2fcbc 100644 --- a/kernel/locking/osq_lock.c +++ b/kernel/locking/osq_lock.c @@ -134,20 +134,11 @@ 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; + 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 * -- 2.18.1