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=-5.4 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=unavailable 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 9A473CA9EB9 for ; Wed, 23 Oct 2019 01:39:21 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 660FE2086D for ; Wed, 23 Oct 2019 01:39:21 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=oracle.com header.i=@oracle.com header.b="BuVelkAP" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1733290AbfJWBjU (ORCPT ); Tue, 22 Oct 2019 21:39:20 -0400 Received: from userp2120.oracle.com ([156.151.31.85]:47504 "EHLO userp2120.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730047AbfJWBjT (ORCPT ); Tue, 22 Oct 2019 21:39:19 -0400 Received: from pps.filterd (userp2120.oracle.com [127.0.0.1]) by userp2120.oracle.com (8.16.0.27/8.16.0.27) with SMTP id x9N1YOd8190852; Wed, 23 Oct 2019 01:36:11 GMT DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=oracle.com; h=subject : to : cc : references : from : message-id : date : mime-version : in-reply-to : content-type : content-transfer-encoding; s=corp-2019-08-05; bh=mgnTopzGZ8f1FGKvPSTHhrMy24Rq85HzQQkpuJIKlp0=; b=BuVelkAPmWzz/ViA5GxMxUd6Ilv/ZHMliID3HYO+ysbz6xcFLl0G7qwrW9ZnhZ5+fw5K ZZwhM1WQ1gpb5f91a2e/3a5K45dUKqz8th5DCDbvJQLQfhXq8imBPNdnNJzDlaNpoHbk MtpwAQQ9uayFJCsgXIPxV4TOl4+N6WL5OrEp1fWLAPHtJEr3Ae5bbcqtmT5o/9Nh6ytW BCV30iby7KyJaxOZfvfwdPZ6v+bRwsi0ufN6DxKVo9xw4OiXTuuAcdsjuY8Jq3hxlM9O YCK0rVUp3NoDs/PhwZcs9Sw9XoQZjTDwsW4wqZi80KUm3adpOAZZ4Jpw0VMvsphz52N8 lA== Received: from aserp3030.oracle.com (aserp3030.oracle.com [141.146.126.71]) by userp2120.oracle.com with ESMTP id 2vqu4qt1qa-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Wed, 23 Oct 2019 01:36:11 +0000 Received: from pps.filterd (aserp3030.oracle.com [127.0.0.1]) by aserp3030.oracle.com (8.16.0.27/8.16.0.27) with SMTP id x9N1YE5W158224; Wed, 23 Oct 2019 01:36:10 GMT Received: from userv0121.oracle.com (userv0121.oracle.com [156.151.31.72]) by aserp3030.oracle.com with ESMTP id 2vsx23yaku-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Wed, 23 Oct 2019 01:36:10 +0000 Received: from abhmp0021.oracle.com (abhmp0021.oracle.com [141.146.116.27]) by userv0121.oracle.com (8.14.4/8.13.8) with ESMTP id x9N1a7iT001979; Wed, 23 Oct 2019 01:36:08 GMT Received: from [10.191.28.118] (/10.191.28.118) by default (Oracle Beehive Gateway v4.0) with ESMTP ; Wed, 23 Oct 2019 01:36:07 +0000 Subject: Re: [PATCH v7 3/5] x86/kvm: Add "nopvspin" parameter to disable PV spinlocks To: Sean Christopherson Cc: Vitaly Kuznetsov , linux-kernel@vger.kernel.org, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, x86@kernel.org, pbonzini@redhat.com, rkrcmar@redhat.com, wanpengli@tencent.com, jmattson@google.com, joro@8bytes.org, boris.ostrovsky@oracle.com, jgross@suse.com, peterz@infradead.org, will@kernel.org, linux-hyperv@vger.kernel.org, kvm@vger.kernel.org, mikelley@microsoft.com, kys@microsoft.com, haiyangz@microsoft.com, sthemmin@microsoft.com, sashal@kernel.org, Jonathan Corbet , "H. Peter Anvin" References: <1571649076-2421-1-git-send-email-zhenzhong.duan@oracle.com> <1571649076-2421-4-git-send-email-zhenzhong.duan@oracle.com> <8736fl1071.fsf@vitty.brq.redhat.com> <20191022210355.GR2343@linux.intel.com> From: Zhenzhong Duan Organization: Oracle Corporation Message-ID: Date: Wed, 23 Oct 2019 09:36:00 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:60.0) Gecko/20100101 Thunderbird/60.9.0 MIME-Version: 1.0 In-Reply-To: <20191022210355.GR2343@linux.intel.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Content-Language: en-US X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9418 signatures=668684 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 suspectscore=0 malwarescore=0 phishscore=0 bulkscore=0 spamscore=0 mlxscore=0 mlxlogscore=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1908290000 definitions=main-1910230013 X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9418 signatures=668684 X-Proofpoint-Spam-Details: rule=notspam policy=default 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=8.0.1-1908290000 definitions=main-1910230013 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2019/10/23 5:03, Sean Christopherson wrote: > On Tue, Oct 22, 2019 at 08:46:46PM +0800, Zhenzhong Duan wrote: >> Hi Vitaly, >> >> On 2019/10/22 19:36, Vitaly Kuznetsov wrote: >> >>> Zhenzhong Duan writes: >>> >> ...snip >> >>>> diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c >>>> index 249f14a..3945aa5 100644 >>>> --- a/arch/x86/kernel/kvm.c >>>> +++ b/arch/x86/kernel/kvm.c >>>> @@ -825,18 +825,36 @@ __visible bool __kvm_vcpu_is_preempted(long cpu) >>>> */ >>>> void __init kvm_spinlock_init(void) >>>> { >>>> - /* Does host kernel support KVM_FEATURE_PV_UNHALT? */ >>>> - if (!kvm_para_has_feature(KVM_FEATURE_PV_UNHALT)) >>>> + /* >>>> + * In case host doesn't support KVM_FEATURE_PV_UNHALT there is still an >>>> + * advantage of keeping virt_spin_lock_key enabled: virt_spin_lock() is >>>> + * preferred over native qspinlock when vCPU is preempted. >>>> + */ >>>> + if (!kvm_para_has_feature(KVM_FEATURE_PV_UNHALT)) { >>>> + pr_info("PV spinlocks disabled, no host support.\n"); >>>> return; >>>> + } >>>> + /* >>>> + * Disable PV qspinlock and use native qspinlock when dedicated pCPUs >>>> + * are available. >>>> + */ >>>> if (kvm_para_has_hint(KVM_HINTS_REALTIME)) { >>>> - static_branch_disable(&virt_spin_lock_key); >>>> - return; >>>> + pr_info("PV spinlocks disabled with KVM_HINTS_REALTIME hints.\n"); >>>> + goto out; >>>> } >>>> - /* Don't use the pvqspinlock code if there is only 1 vCPU. */ >>>> - if (num_possible_cpus() == 1) >>>> - return; >>>> + if (num_possible_cpus() == 1) { >>>> + pr_info("PV spinlocks disabled, single CPU.\n"); >>>> + goto out; >>>> + } >>>> + >>>> + if (nopvspin) { >>>> + pr_info("PV spinlocks disabled, forced by \"nopvspin\" parameter.\n"); >>>> + goto out; >>>> + } >>>> + >>>> + pr_info("PV spinlocks enabled\n"); >>>> __pv_init_lock_hash(); >>>> pv_ops.lock.queued_spin_lock_slowpath = __pv_queued_spin_lock_slowpath; >>>> @@ -849,6 +867,8 @@ void __init kvm_spinlock_init(void) >>>> pv_ops.lock.vcpu_is_preempted = >>>> PV_CALLEE_SAVE(__kvm_vcpu_is_preempted); >>>> } >>>> +out: >>>> + static_branch_disable(&virt_spin_lock_key); >>> You probably need to add 'return' before 'out:' as it seems you're >>> disabling virt_spin_lock_key in all cases now). >> virt_spin_lock_key is kept enabled in !kvm_para_has_feature(KVM_FEATURE_PV_UNHALT) >> case which is the only case virt_spin_lock() optimization is used. >> >> When PV qspinlock is enabled, virt_spin_lock() isn't called in >> __pv_queued_spin_lock_slowpath() in which case we don't care >> virt_spin_lock_key's value. >> >> So adding 'return' or not are both ok, I chosed to save a line, >> let me know if you prefer to add a 'return' and I'll change it. > It'd be worth adding a comment here if you end up spinning another version > to change the logging prefix. The logic is sound and I like the end > result, but I had the same knee jerk "this can't be right!?!?" reaction as > Vitaly. Sure, will do in next version. Thanks Zhenzhong