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=-2.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,URIBL_BLOCKED,USER_AGENT_MUTT 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 ABDA4C5CFE7 for ; Wed, 11 Jul 2018 18:18:42 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 740A4208E5 for ; Wed, 11 Jul 2018 18:18:42 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 740A4208E5 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=linux.vnet.ibm.com 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 S2387720AbeGKSYK (ORCPT ); Wed, 11 Jul 2018 14:24:10 -0400 Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:47846 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1732496AbeGKSYJ (ORCPT ); Wed, 11 Jul 2018 14:24:09 -0400 Received: from pps.filterd (m0098394.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.16.0.22/8.16.0.22) with SMTP id w6BIEKGG134430 for ; Wed, 11 Jul 2018 14:18:38 -0400 Received: from e12.ny.us.ibm.com (e12.ny.us.ibm.com [129.33.205.202]) by mx0a-001b2d01.pphosted.com with ESMTP id 2k5md9ewcw-1 (version=TLSv1.2 cipher=AES256-GCM-SHA384 bits=256 verify=NOT) for ; Wed, 11 Jul 2018 14:18:38 -0400 Received: from localhost by e12.ny.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Wed, 11 Jul 2018 14:18:37 -0400 Received: from b01cxnp22034.gho.pok.ibm.com (9.57.198.24) by e12.ny.us.ibm.com (146.89.104.199) with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted; (version=TLSv1/SSLv3 cipher=AES256-GCM-SHA384 bits=256/256) Wed, 11 Jul 2018 14:18:34 -0400 Received: from b01ledav003.gho.pok.ibm.com (b01ledav003.gho.pok.ibm.com [9.57.199.108]) by b01cxnp22034.gho.pok.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id w6BIIYjT55509042 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=FAIL); Wed, 11 Jul 2018 18:18:34 GMT Received: from b01ledav003.gho.pok.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 63DF7B205F; Wed, 11 Jul 2018 14:18:33 -0400 (EDT) Received: from b01ledav003.gho.pok.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 45A03B2065; Wed, 11 Jul 2018 14:18:33 -0400 (EDT) Received: from paulmck-ThinkPad-W541 (unknown [9.70.82.159]) by b01ledav003.gho.pok.ibm.com (Postfix) with ESMTP; Wed, 11 Jul 2018 14:18:33 -0400 (EDT) Received: by paulmck-ThinkPad-W541 (Postfix, from userid 1000) id 3C5E316C3B6E; Wed, 11 Jul 2018 11:20:53 -0700 (PDT) Date: Wed, 11 Jul 2018 11:20:53 -0700 From: "Paul E. McKenney" To: David Woodhouse Cc: peterz@infradead.org, mhillenb@amazon.de, linux-kernel@vger.kernel.org, kvm@vger.kernel.org Subject: Re: [PATCH v2] kvm/x86: Inform RCU of quiescent state when entering guest mode Reply-To: paulmck@linux.vnet.ibm.com References: <20180711174843.GX3593@linux.vnet.ibm.com> <20180711180101.3711464-1-dwmw2@infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180711180101.3711464-1-dwmw2@infradead.org> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-GCONF: 00 x-cbid: 18071118-0060-0000-0000-0000028AB197 X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00009352; HX=3.00000241; KW=3.00000007; PH=3.00000004; SC=3.00000266; SDB=6.01059892; UDB=6.00544003; IPR=6.00837812; MB=3.00022105; MTD=3.00000008; XFM=3.00000015; UTC=2018-07-11 18:18:36 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 18071118-0061-0000-0000-000045C323D1 Message-Id: <20180711182053.GA3593@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2018-07-11_04:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 malwarescore=0 suspectscore=0 phishscore=0 bulkscore=0 spamscore=0 clxscore=1015 lowpriorityscore=0 mlxscore=0 impostorscore=0 mlxlogscore=961 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1806210000 definitions=main-1807110193 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Jul 11, 2018 at 07:01:01PM +0100, David Woodhouse wrote: > From: David Woodhouse > > RCU can spend long periods of time waiting for a CPU which is actually in > KVM guest mode, entirely pointlessly. Treat it like the idle and userspace > modes, and don't wait for it. > > Signed-off-by: David Woodhouse And idiot here forgot about some of the debugging code in RCU's dyntick-idle code. I will reply with a fixed patch. The code below works just fine as long as you don't enable CONFIG_RCU_EQS_DEBUG, so should be OK for testing, just not for mainline. Thanx, Paul > --- > arch/x86/kvm/x86.c | 2 ++ > include/linux/rcupdate.h | 7 +++++++ > kernel/rcu/tree.c | 2 ++ > 3 files changed, 11 insertions(+) > > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c > index 0046aa70205a..b0c82f70afa7 100644 > --- a/arch/x86/kvm/x86.c > +++ b/arch/x86/kvm/x86.c > @@ -7458,7 +7458,9 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu) > vcpu->arch.switch_db_regs &= ~KVM_DEBUGREG_RELOAD; > } > > + rcu_kvm_enter(); > kvm_x86_ops->run(vcpu); > + rcu_kvm_exit(); > > /* > * Do this here before restoring debug registers on the host. And > diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h > index 65163aa0bb04..1325f9d9ce00 100644 > --- a/include/linux/rcupdate.h > +++ b/include/linux/rcupdate.h > @@ -212,6 +212,13 @@ do { \ > #error "Unknown RCU implementation specified to kernel configuration" > #endif > > +/* > + * These are currently identical to the _idle_ versions but let's > + * explicitly have separate copies to keep Paul honest in future. > + */ > +static inline void rcu_kvm_enter(void) { rcu_idle_enter(); } > +static inline void rcu_kvm_exit(void) { rcu_idle_exit(); } > + > /* > * The init_rcu_head_on_stack() and destroy_rcu_head_on_stack() calls > * are needed for dynamic initialization and destruction of rcu_head > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c > index aa7cade1b9f3..d38c381bf4e3 100644 > --- a/kernel/rcu/tree.c > +++ b/kernel/rcu/tree.c > @@ -760,6 +760,7 @@ void rcu_idle_enter(void) > lockdep_assert_irqs_disabled(); > rcu_eqs_enter(false); > } > +EXPORT_SYMBOL_GPL(rcu_idle_enter); > > #ifdef CONFIG_NO_HZ_FULL > /** > @@ -913,6 +914,7 @@ void rcu_idle_exit(void) > rcu_eqs_exit(false); > local_irq_restore(flags); > } > +EXPORT_SYMBOL_GPL(rcu_idle_exit); > > #ifdef CONFIG_NO_HZ_FULL > /** > -- > 2.17.1 >