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=-6.8 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,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 561DAC4360C for ; Thu, 10 Oct 2019 08:50:57 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 2C6E8208C3 for ; Thu, 10 Oct 2019 08:50:57 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1570697457; bh=ltpmpVIfpVjSRY1nFe8HZMAvP9cNBcb938J+Gx1/Yr0=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=sK7YeW1fkLDHGb1JrkoHIjB1dMRxSqiIARnEutmBXPallRMONOTZUTD7vFtK5aZ5H ZgmVz2n/o+w1yQEIp0ozwk465iZ/Y8zEQubOIuKheL/2+q0xniiIcytUoJh/s/o/Hp Z2mT9cnejncnd5U4J8jJiS4RCEss8GV1Z0BYgMqE= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2390040AbfJJIuz (ORCPT ); Thu, 10 Oct 2019 04:50:55 -0400 Received: from mail.kernel.org ([198.145.29.99]:58068 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2390029AbfJJIuu (ORCPT ); Thu, 10 Oct 2019 04:50:50 -0400 Received: from localhost (83-86-89-107.cable.dynamic.v4.ziggo.nl [83.86.89.107]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id ECE2421929; Thu, 10 Oct 2019 08:50:48 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1570697449; bh=ltpmpVIfpVjSRY1nFe8HZMAvP9cNBcb938J+Gx1/Yr0=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=vX92p1J7yuEQP9GK9I1pWdepkhoMDqVkOaYcFrqjP0cA7yZLvz5/orzfQ1+IQwqB9 0wdn6ZHJCYBRxLQZ8uIAvxj3geVncRvgGOhDl+luFdQY94HDLA7r/uGxv1PkCjA62c hVAdm67hXUw2OY5APigUENdKU3VCvSoktxHauav0= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, loobinliu@tencent.com, Peter Zijlstra , Thomas Gleixner , Ingo Molnar , Waiman Long , Paolo Bonzini , =?UTF-8?q?Radim=20Kr=C4=8Dm=C3=A1=C5=99?= , Wanpeng Li Subject: [PATCH 4.14 24/61] Revert "locking/pvqspinlock: Dont wait if vCPU is preempted" Date: Thu, 10 Oct 2019 10:36:49 +0200 Message-Id: <20191010083504.491883659@linuxfoundation.org> X-Mailer: git-send-email 2.23.0 In-Reply-To: <20191010083449.500442342@linuxfoundation.org> References: <20191010083449.500442342@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Wanpeng Li commit 89340d0935c9296c7b8222b6eab30e67cb57ab82 upstream. This patch reverts commit 75437bb304b20 (locking/pvqspinlock: Don't wait if vCPU is preempted). A large performance regression was caused by this commit. on over-subscription scenarios. The test was run on a Xeon Skylake box, 2 sockets, 40 cores, 80 threads, with three VMs of 80 vCPUs each. The score of ebizzy -M is reduced from 13000-14000 records/s to 1700-1800 records/s: Host Guest score vanilla w/o kvm optimizations upstream 1700-1800 records/s vanilla w/o kvm optimizations revert 13000-14000 records/s vanilla w/ kvm optimizations upstream 4500-5000 records/s vanilla w/ kvm optimizations revert 14000-15500 records/s Exit from aggressive wait-early mechanism can result in premature yield and extra scheduling latency. Actually, only 6% of wait_early events are caused by vcpu_is_preempted() being true. However, when one vCPU voluntarily releases its vCPU, all the subsequently waiters in the queue will do the same and the cascading effect leads to bad performance. kvm optimizations: [1] commit d73eb57b80b (KVM: Boost vCPUs that are delivering interrupts) [2] commit 266e85a5ec9 (KVM: X86: Boost queue head vCPU to mitigate lock waiter preemption) Tested-by: loobinliu@tencent.com Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: Ingo Molnar Cc: Waiman Long Cc: Paolo Bonzini Cc: Radim Krčmář Cc: loobinliu@tencent.com Cc: stable@vger.kernel.org Fixes: 75437bb304b20 (locking/pvqspinlock: Don't wait if vCPU is preempted) Signed-off-by: Wanpeng Li Signed-off-by: Paolo Bonzini Signed-off-by: Greg Kroah-Hartman --- kernel/locking/qspinlock_paravirt.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) --- a/kernel/locking/qspinlock_paravirt.h +++ b/kernel/locking/qspinlock_paravirt.h @@ -247,7 +247,7 @@ pv_wait_early(struct pv_node *prev, int if ((loop & PV_PREV_CHECK_MASK) != 0) return false; - return READ_ONCE(prev->state) != vcpu_running || vcpu_is_preempted(prev->cpu); + return READ_ONCE(prev->state) != vcpu_running; } /*