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=0.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,URG_BIZ autolearn=no 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 65F7EC5CFE7 for ; Wed, 11 Jul 2018 18:32:08 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 0DBBA20C51 for ; Wed, 11 Jul 2018 18:32:08 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 0DBBA20C51 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=de.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 S2388277AbeGKShi (ORCPT ); Wed, 11 Jul 2018 14:37:38 -0400 Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:40208 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1732344AbeGKShi (ORCPT ); Wed, 11 Jul 2018 14:37:38 -0400 Received: from pps.filterd (m0098416.ppops.net [127.0.0.1]) by mx0b-001b2d01.pphosted.com (8.16.0.22/8.16.0.22) with SMTP id w6BITPH7011940 for ; Wed, 11 Jul 2018 14:32:03 -0400 Received: from e06smtp03.uk.ibm.com (e06smtp03.uk.ibm.com [195.75.94.99]) by mx0b-001b2d01.pphosted.com with ESMTP id 2k5mcwqaym-1 (version=TLSv1.2 cipher=AES256-GCM-SHA384 bits=256 verify=NOT) for ; Wed, 11 Jul 2018 14:32:03 -0400 Received: from localhost by e06smtp03.uk.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! 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Violators will be prosecuted; (version=TLSv1/SSLv3 cipher=AES256-GCM-SHA384 bits=256/256) Wed, 11 Jul 2018 19:31:57 +0100 Received: from d06av23.portsmouth.uk.ibm.com (d06av23.portsmouth.uk.ibm.com [9.149.105.59]) by b06cxnps4076.portsmouth.uk.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id w6BIVug729032536 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=FAIL); Wed, 11 Jul 2018 18:31:56 GMT Received: from d06av23.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 4F080A4053; Wed, 11 Jul 2018 21:32:18 +0100 (BST) Received: from d06av23.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 01D94A4057; Wed, 11 Jul 2018 21:32:18 +0100 (BST) Received: from oc7330422307.ibm.com (unknown [9.145.165.185]) by d06av23.portsmouth.uk.ibm.com (Postfix) with ESMTP; Wed, 11 Jul 2018 21:32:17 +0100 (BST) Subject: Re: [RFC] Make need_resched() return true when rcu_urgent_qs requested To: David Woodhouse , paulmck@linux.vnet.ibm.com Cc: Peter Zijlstra , mhillenb@amazon.de, linux-kernel , kvm References: <20180709163432.GV3593@linux.vnet.ibm.com> <1531162254.26547.3.camel@infradead.org> <20180709203441.GE3593@linux.vnet.ibm.com> <1531168538.26547.5.camel@infradead.org> <20180709204248.GF3593@linux.vnet.ibm.com> <1531169145.26547.8.camel@infradead.org> <20180709210532.GH3593@linux.vnet.ibm.com> <20180709220823.GA18045@linux.vnet.ibm.com> <1531319025.8759.57.camel@infradead.org> <20180711144303.GQ3593@linux.vnet.ibm.com> <20180711164952.GA29994@linux.vnet.ibm.com> From: Christian Borntraeger Openpgp: preference=signencrypt Autocrypt: addr=borntraeger@de.ibm.com; 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Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.8.0 MIME-Version: 1.0 In-Reply-To: Content-Language: en-US X-TM-AS-GCONF: 00 x-cbid: 18071118-0012-0000-0000-00000289236C X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 18071118-0013-0000-0000-000020BAC746 Message-Id: <9ee4d6fd-02e2-2c73-36a7-36ef4f6413b0@de.ibm.com> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit 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=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1806210000 definitions=main-1807110195 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org So why is the rcu_virt_note_context_switch(smp_processor_id()); in guest_enter_irqoff not good enough? This was actually supposed to tell rcu that being in the guest is an extended quiescing period (like userspace). What has changed? On 07/11/2018 07:03 PM, David Woodhouse wrote: > On Wed, 2018-07-11 at 09:49 -0700, Paul E. McKenney wrote: >> And here is an updated v4.15 patch with Marius's Reported-by and David's >> fix to my lost exclamation point. > > Thanks. Are you sending the original version of that to Linus? It'd be > useful to have the commit ID so that we can watch for it landing, and > chase this one up to Greg. > > As discussed on IRC, this patch reduces synchronize_sched() latency for > us from ~4600s to ~160ms, which is nice. > > However, it isn't going to be sufficient in the NO_HZ_FULL case. For > that you want a patch like the one below, which happily reduces the > latency in our (!NO_HZ_FULL) case still further to ~40ms. > > Adding kvm list for better review... > > From: David Woodhouse > Subject: [PATCH] kvm/x86: Inform RCU of quiescent state when entering guest mode > > 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 > --- > arch/x86/kvm/x86.c | 2 ++ > include/linux/rcutree.h | 2 ++ > kernel/rcu/tree.c | 16 ++++++++++++++++ > 3 files changed, 20 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/rcutree.h b/include/linux/rcutree.h > index 914655848ef6..6d07af5a50fc 100644 > --- a/include/linux/rcutree.h > +++ b/include/linux/rcutree.h > @@ -82,6 +82,8 @@ void cond_synchronize_sched(unsigned long oldstate); > > void rcu_idle_enter(void); > void rcu_idle_exit(void); > +void rcu_kvm_enter(void); > +void rcu_kvm_exit(void); > void rcu_irq_enter(void); > void rcu_irq_exit(void); > void rcu_irq_enter_irqson(void); > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c > index aa7cade1b9f3..df7893273939 100644 > --- a/kernel/rcu/tree.c > +++ b/kernel/rcu/tree.c > @@ -1019,6 +1019,22 @@ void rcu_irq_enter_irqson(void) > local_irq_restore(flags); > } > > +/* > + * These are currently identical to the _idle_ versions but let's > + * explicitly have separate copies to keep Paul honest in future. > + */ > +void rcu_kvm_enter(void) > +{ > + rcu_idle_enter(); > +} > +EXPORT_SYMBOL_GPL(rcu_kvm_enter); > + > +void rcu_kvm_exit(void) > +{ > + rcu_idle_exit(); > +} > +EXPORT_SYMBOL_GPL(rcu_kvm_exit); > + > /** > * rcu_is_watching - see if RCU thinks that the current CPU is idle > * >