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 639A6CA9EB7 for ; Tue, 22 Oct 2019 12:49:03 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 3AA1B2075A for ; Tue, 22 Oct 2019 12:49:03 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=oracle.com header.i=@oracle.com header.b="VW246wRq" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730590AbfJVMs4 (ORCPT ); Tue, 22 Oct 2019 08:48:56 -0400 Received: from userp2130.oracle.com ([156.151.31.86]:44874 "EHLO userp2130.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730275AbfJVMs4 (ORCPT ); Tue, 22 Oct 2019 08:48:56 -0400 Received: from pps.filterd (userp2130.oracle.com [127.0.0.1]) by userp2130.oracle.com (8.16.0.27/8.16.0.27) with SMTP id x9MCiXqG163323; Tue, 22 Oct 2019 12:47:03 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=vppjsuM3aTkGtdL8I7GSga2BnR0QS2xZhjmHJAapcRs=; b=VW246wRq2ra3oMJ9vKt5fVKA+KTK+wOv6OMe94YWzjkyhPofjnexN6dHhI7LGpy8vu88 QUl2BgRNgDbNMyGu/B3E79uq/k/UgJBu5bKRKGmMquvLIejqbY2MFNOhRKTEq0KB1pPp HfulBIB0e8XPaTz0qBmbZvYVo35I41aEE1qMCmALXDbagFrxQM43y9AUMCnM10tcD+Ai lhj5gV5Q7z71UWSc/yISGbQAb3ujeF7bvogHeb+jYT9kS9u8PlMSoxMmwrQw17mBB5wt RcYqD5SbLsCPu94011J5I8HxhFyA8fxuyvFgNG3KhfvuWpG92PTsogbRmgPKoc6Z2QL8 6Q== Received: from userp3020.oracle.com (userp3020.oracle.com [156.151.31.79]) by userp2130.oracle.com with ESMTP id 2vqswtefrx-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Tue, 22 Oct 2019 12:47:03 +0000 Received: from pps.filterd (userp3020.oracle.com [127.0.0.1]) by userp3020.oracle.com (8.16.0.27/8.16.0.27) with SMTP id x9MCiE69049644; Tue, 22 Oct 2019 12:47:02 GMT Received: from userv0121.oracle.com (userv0121.oracle.com [156.151.31.72]) by userp3020.oracle.com with ESMTP id 2vsp3y58ge-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Tue, 22 Oct 2019 12:47:02 +0000 Received: from abhmp0002.oracle.com (abhmp0002.oracle.com [141.146.116.8]) by userv0121.oracle.com (8.14.4/8.13.8) with ESMTP id x9MCktk2017217; Tue, 22 Oct 2019 12:46:57 GMT Received: from [10.191.9.53] (/10.191.9.53) by default (Oracle Beehive Gateway v4.0) with ESMTP ; Tue, 22 Oct 2019 05:46:54 -0700 Subject: Re: [PATCH v7 3/5] x86/kvm: Add "nopvspin" parameter to disable PV spinlocks To: Vitaly Kuznetsov , linux-kernel@vger.kernel.org Cc: tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, x86@kernel.org, pbonzini@redhat.com, rkrcmar@redhat.com, sean.j.christopherson@intel.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> From: Zhenzhong Duan Organization: Oracle Corporation Message-ID: Date: Tue, 22 Oct 2019 20:46:46 +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: <8736fl1071.fsf@vitty.brq.redhat.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=9417 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-1910220117 X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9417 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-1910220117 Sender: linux-hyperv-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-hyperv@vger.kernel.org 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. btw: __pv_queued_spin_lock_slowpath() is alias of queued_spin_lock_slowpath() Thanks Zhenzhong