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=-2.4 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,UNPARSEABLE_RELAY,USER_AGENT_SANE_1 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 B9896ECE58C for ; Mon, 7 Oct 2019 14:48:40 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 88F5021721 for ; Mon, 7 Oct 2019 14:48:40 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=oracle.com header.i=@oracle.com header.b="hrnkujhq" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727589AbfJGOsg (ORCPT ); Mon, 7 Oct 2019 10:48:36 -0400 Received: from userp2130.oracle.com ([156.151.31.86]:50714 "EHLO userp2130.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727490AbfJGOsf (ORCPT ); Mon, 7 Oct 2019 10:48:35 -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 x97EiEY1125543; Mon, 7 Oct 2019 14:46:36 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=4N9yoYf9MRwUqpnd56wp98SUWYHADiH5FtpOOJuf0gk=; b=hrnkujhqdN3DqHnzuVtsRmqrQ0R7uDmpTRgE/e9INNY9Nf+88ILdGWOZBBr2Dz/j1D+H 0jhX0ewC4939ghw+fFmBaWmoGz4Zdt+KtdmB7IZtyMMLWAR19wX567LSITKc7LGF04uf G3NLFUEpj7CnPN0AhHaK8dRiCbl0WKYEIRYt+ZxP/jVo8mhtQ6SBe+QGQZPIzBE5ph2z /TOoXLoRI50fZhMSqof6MOJk+xR3N5FLCkG/ldCr7uHtOnXixbCAcA2atzoe3fFDNhp6 7YZjgP26XmT4LrC/mssrMXOU0xObtzMiXfr7T0H25OTgDs4xG9idsOC/LQpDSUzKcTPM 8Q== Received: from aserp3020.oracle.com (aserp3020.oracle.com [141.146.126.70]) by userp2130.oracle.com with ESMTP id 2vejku784w-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Mon, 07 Oct 2019 14:46:36 +0000 Received: from pps.filterd (aserp3020.oracle.com [127.0.0.1]) by aserp3020.oracle.com (8.16.0.27/8.16.0.27) with SMTP id x97Ejixh071811; Mon, 7 Oct 2019 14:46:35 GMT Received: from aserv0122.oracle.com (aserv0122.oracle.com [141.146.126.236]) by aserp3020.oracle.com with ESMTP id 2vf4phnq3j-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Mon, 07 Oct 2019 14:46:35 +0000 Received: from abhmp0003.oracle.com (abhmp0003.oracle.com [141.146.116.9]) by aserv0122.oracle.com (8.14.4/8.14.4) with ESMTP id x97EkNxG019145; Mon, 7 Oct 2019 14:46:24 GMT Received: from bostrovs-us.us.oracle.com (/10.152.32.65) by default (Oracle Beehive Gateway v4.0) with ESMTP ; Mon, 07 Oct 2019 07:46:23 -0700 Subject: Re: [PATCH v4 1/4] x86/kvm: Add "nopvspin" parameter to disable PV spinlocks To: Zhenzhong Duan , linux-kernel@vger.kernel.org Cc: vkuznets@redhat.com, linux-hyperv@vger.kernel.org, kvm@vger.kernel.org, kys@microsoft.com, haiyangz@microsoft.com, sthemmin@microsoft.com, sashal@kernel.org, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, pbonzini@redhat.com, rkrcmar@redhat.com, sean.j.christopherson@intel.com, wanpengli@tencent.com, jmattson@google.com, joro@8bytes.org, jgross@suse.com, sstabellini@kernel.org, peterz@infradead.org, Jonathan Corbet , "H. Peter Anvin" , Will Deacon References: <1570111335-12731-1-git-send-email-zhenzhong.duan@oracle.com> <1570111335-12731-2-git-send-email-zhenzhong.duan@oracle.com> <26ef7beb-dad0-13c9-fc2f-217a5e046e4d@oracle.com> From: Boris Ostrovsky Openpgp: preference=signencrypt Autocrypt: addr=boris.ostrovsky@oracle.com; prefer-encrypt=mutual; keydata= mQINBFH8CgsBEAC0KiOi9siOvlXatK2xX99e/J3OvApoYWjieVQ9232Eb7GzCWrItCzP8FUV PQg8rMsSd0OzIvvjbEAvaWLlbs8wa3MtVLysHY/DfqRK9Zvr/RgrsYC6ukOB7igy2PGqZd+M MDnSmVzik0sPvB6xPV7QyFsykEgpnHbvdZAUy/vyys8xgT0PVYR5hyvhyf6VIfGuvqIsvJw5 C8+P71CHI+U/IhsKrLrsiYHpAhQkw+Zvyeml6XSi5w4LXDbF+3oholKYCkPwxmGdK8MUIdkM d7iYdKqiP4W6FKQou/lC3jvOceGupEoDV9botSWEIIlKdtm6C4GfL45RD8V4B9iy24JHPlom woVWc0xBZboQguhauQqrBFooHO3roEeM1pxXjLUbDtH4t3SAI3gt4dpSyT3EvzhyNQVVIxj2 FXnIChrYxR6S0ijSqUKO0cAduenhBrpYbz9qFcB/GyxD+ZWY7OgQKHUZMWapx5bHGQ8bUZz2 SfjZwK+GETGhfkvNMf6zXbZkDq4kKB/ywaKvVPodS1Poa44+B9sxbUp1jMfFtlOJ3AYB0WDS Op3d7F2ry20CIf1Ifh0nIxkQPkTX7aX5rI92oZeu5u038dHUu/dO2EcuCjl1eDMGm5PLHDSP 0QUw5xzk1Y8MG1JQ56PtqReO33inBXG63yTIikJmUXFTw6lLJwARAQABtDNCb3JpcyBPc3Ry b3Zza3kgKFdvcmspIDxib3Jpcy5vc3Ryb3Zza3lAb3JhY2xlLmNvbT6JAjgEEwECACIFAlH8 CgsCGwMGCwkIBwMCBhUIAgkKCwQWAgMBAh4BAheAAAoJEIredpCGysGyasEP/j5xApopUf4g 9Fl3UxZuBx+oduuw3JHqgbGZ2siA3EA4bKwtKq8eT7ekpApn4c0HA8TWTDtgZtLSV5IdH+9z JimBDrhLkDI3Zsx2CafL4pMJvpUavhc5mEU8myp4dWCuIylHiWG65agvUeFZYK4P33fGqoaS VGx3tsQIAr7MsQxilMfRiTEoYH0WWthhE0YVQzV6kx4wj4yLGYPPBtFqnrapKKC8yFTpgjaK jImqWhU9CSUAXdNEs/oKVR1XlkDpMCFDl88vKAuJwugnixjbPFTVPyoC7+4Bm/FnL3iwlJVE qIGQRspt09r+datFzPqSbp5Fo/9m4JSvgtPp2X2+gIGgLPWp2ft1NXHHVWP19sPgEsEJXSr9 tskM8ScxEkqAUuDs6+x/ISX8wa5Pvmo65drN+JWA8EqKOHQG6LUsUdJolFM2i4Z0k40BnFU/ kjTARjrXW94LwokVy4x+ZYgImrnKWeKac6fMfMwH2aKpCQLlVxdO4qvJkv92SzZz4538az1T m+3ekJAimou89cXwXHCFb5WqJcyjDfdQF857vTn1z4qu7udYCuuV/4xDEhslUq1+GcNDjAhB nNYPzD+SvhWEsrjuXv+fDONdJtmLUpKs4Jtak3smGGhZsqpcNv8nQzUGDQZjuCSmDqW8vn2o hWwveNeRTkxh+2x1Qb3GT46uuQINBFH8CgsBEADGC/yx5ctcLQlB9hbq7KNqCDyZNoYu1HAB Hal3MuxPfoGKObEktawQPQaSTB5vNlDxKihezLnlT/PKjcXC2R1OjSDinlu5XNGc6mnky03q yymUPyiMtWhBBftezTRxWRslPaFWlg/h/Y1iDuOcklhpr7K1h1jRPCrf1yIoxbIpDbffnuyz kuto4AahRvBU4Js4sU7f/btU+h+e0AcLVzIhTVPIz7PM+Gk2LNzZ3/on4dnEc/qd+ZZFlOQ4 KDN/hPqlwA/YJsKzAPX51L6Vv344pqTm6Z0f9M7YALB/11FO2nBB7zw7HAUYqJeHutCwxm7i BDNt0g9fhviNcJzagqJ1R7aPjtjBoYvKkbwNu5sWDpQ4idnsnck4YT6ctzN4I+6lfkU8zMzC gM2R4qqUXmxFIS4Bee+gnJi0Pc3KcBYBZsDK44FtM//5Cp9DrxRQOh19kNHBlxkmEb8kL/pw XIDcEq8MXzPBbxwHKJ3QRWRe5jPNpf8HCjnZz0XyJV0/4M1JvOua7IZftOttQ6KnM4m6WNIZ 2ydg7dBhDa6iv1oKdL7wdp/rCulVWn8R7+3cRK95SnWiJ0qKDlMbIN8oGMhHdin8cSRYdmHK kTnvSGJNlkis5a+048o0C6jI3LozQYD/W9wq7MvgChgVQw1iEOB4u/3FXDEGulRVko6xCBU4 SQARAQABiQIfBBgBAgAJBQJR/AoLAhsMAAoJEIredpCGysGyfvMQAIywR6jTqix6/fL0Ip8G jpt3uk//QNxGJE3ZkUNLX6N786vnEJvc1beCu6EwqD1ezG9fJKMl7F3SEgpYaiKEcHfoKGdh 30B3Hsq44vOoxR6zxw2B/giADjhmWTP5tWQ9548N4VhIZMYQMQCkdqaueSL+8asp8tBNP+TJ PAIIANYvJaD8xA7sYUXGTzOXDh2THWSvmEWWmzok8er/u6ZKdS1YmZkUy8cfzrll/9hiGCTj u3qcaOM6i/m4hqtvsI1cOORMVwjJF4+IkC5ZBoeRs/xW5zIBdSUoC8L+OCyj5JETWTt40+lu qoqAF/AEGsNZTrwHJYu9rbHH260C0KYCNqmxDdcROUqIzJdzDKOrDmebkEVnxVeLJBIhYZUd t3Iq9hdjpU50TA6sQ3mZxzBdfRgg+vaj2DsJqI5Xla9QGKD+xNT6v14cZuIMZzO7w0DoojM4 ByrabFsOQxGvE0w9Dch2BDSI2Xyk1zjPKxG1VNBQVx3flH37QDWpL2zlJikW29Ws86PHdthh Fm5PY8YtX576DchSP6qJC57/eAAe/9ztZdVAdesQwGb9hZHJc75B+VNm4xrh/PJO6c1THqdQ 19WVJ+7rDx3PhVncGlbAOiiiE3NOFPJ1OQYxPKtpBUukAlOTnkKE6QcA4zckFepUkfmBV1wM Jg6OxFYd01z+a+oL Message-ID: Date: Mon, 7 Oct 2019 10:46:03 -0400 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.7.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Content-Language: en-US X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9403 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-1910070147 X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9403 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-1910070147 Sender: linux-hyperv-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-hyperv@vger.kernel.org On 10/6/19 3:49 AM, Zhenzhong Duan wrote: > On 2019/10/4 22:52, Boris Ostrovsky wrote: > >> On 10/3/19 10:02 AM, Zhenzhong Duan wrote: >>>   void __init kvm_spinlock_init(void) >>>   { >>> -    /* Does host kernel support KVM_FEATURE_PV_UNHALT? */ >>> -    if (!kvm_para_has_feature(KVM_FEATURE_PV_UNHALT)) >>> -        return; >>> - >>> -    if (kvm_para_has_hint(KVM_HINTS_REALTIME)) >>> +    /* >>> +     * Don't use the pvqspinlock code if no KVM_FEATURE_PV_UNHALT >>> feature >>> +     * support, or there is REALTIME hints or only 1 vCPU. >>> +     */ >>> +    if (!kvm_para_has_feature(KVM_FEATURE_PV_UNHALT) || >>> +        kvm_para_has_hint(KVM_HINTS_REALTIME) || >>> +        num_possible_cpus() == 1) { >>> +        pr_info("PV spinlocks disabled\n"); >>>           return; >>> +    } >>>   -    /* Don't use the pvqspinlock code if there is only 1 vCPU. */ >>> -    if (num_possible_cpus() == 1) >>> +    if (nopvspin) { >>> +        pr_info("PV spinlocks disabled forced by \"nopvspin\" >>> parameter.\n"); >>> +        static_branch_disable(&virt_spin_lock_key); >> Would it make sense to bring here the other site where the key is >> disabled (in kvm_smp_prepare_cpus())? > > Thanks for point out, I'll do it. Just not clear if I should do that > in a separate patch, > there is a history about that code: > > Its original place was here and then moved to kvm_smp_prepare_cpus() > by below commit: > 34226b6b ("KVM: X86: Fix setup the virt_spin_lock_key before static > key get initialized") > which fixed jump_label_init() calling late issue. > > Then 8990cac6 ("x86/jump_label: Initialize static branching early") > move jump_label_init() > early, so commit 34226b6b could be reverted. Which is similar to what you did earlier for Xen. > >> >> (and, in fact, shouldn't all of the checks that result in early return >> above disable the key?) > > I think we should enable he key for > !kvm_para_has_feature(KVM_FEATURE_PV_UNHALT) case, > there is lock holder preemption issue as qspinlock is fair lock, > virt_spin_lock() > is an optimization to that, imaging one pcpu running 10 vcpus of same > guest > contending a same lock. Right. I conflated pv lock and virt_spin_lock_key, and that is wrong. -boris > > For kvm_para_has_hint(KVM_HINTS_REALTIME) case, hypervisor hints there is > no preemption and we should disable virt_spin_lock_key to use native > qspinlock. > > For the UP case, we don't care virt_spin_lock_key value. > > For nopvspin case, we intentionally check native qspinlock code > performance, > compare it with PV qspinlock, etc. So virt_spin_lock() optimization > should be disabled. > > Let me know if anything wrong with above understanding. Thanks > > Zhenzhong >