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,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 2502BC43331 for ; Tue, 12 Nov 2019 12:19:25 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id E55CD2084E for ; Tue, 12 Nov 2019 12:19:24 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=oracle.com header.i=@oracle.com header.b="MwYUSKkD" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1725919AbfKLMTY (ORCPT ); Tue, 12 Nov 2019 07:19:24 -0500 Received: from userp2130.oracle.com ([156.151.31.86]:46782 "EHLO userp2130.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725865AbfKLMTY (ORCPT ); Tue, 12 Nov 2019 07:19:24 -0500 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 xACC92uk119335; Tue, 12 Nov 2019 12:19:19 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=vJi+sgSpT/msCu8MaaZcjY30BS9nxFhGVS/H9KWglz8=; b=MwYUSKkDy7qhbAyxsaSs4Pe7s3VeJaZi5XFd6CkjEqcHjkAxXXmHveei75re0JsT+VdH /IGRzoK4euLvB66LenmKhgQ8XEJTjWhYQ51M/GQ6cAhu21JhfKABtk1R5tmyI7WZzQGj hJl29MYPUVkajnbjP41qYT4O/5xbjuSCZQndzqEsr8mOQciFD5nNDaR1RHAeeJot+g37 1c8d5cbrI8FjDijZJgyxcvqT+NMd2QN5h0wzPSCHt8Wc6YpznsGlAQyf2VYXBomd7gGU hGTZ50wHPln8NK4nApccWUQZzDkgFBmjxEckKD57bDB4FQe6yct2Usd6UymVJWtu/UOG Hg== Received: from userp3030.oracle.com (userp3030.oracle.com [156.151.31.80]) by userp2130.oracle.com with ESMTP id 2w5mvtmdr8-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Tue, 12 Nov 2019 12:19:19 +0000 Received: from pps.filterd (userp3030.oracle.com [127.0.0.1]) by userp3030.oracle.com (8.16.0.27/8.16.0.27) with SMTP id xACC8n55137438; Tue, 12 Nov 2019 12:19:18 GMT Received: from aserv0121.oracle.com (aserv0121.oracle.com [141.146.126.235]) by userp3030.oracle.com with ESMTP id 2w7khk7hvn-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Tue, 12 Nov 2019 12:19:18 +0000 Received: from abhmp0022.oracle.com (abhmp0022.oracle.com [141.146.116.28]) by aserv0121.oracle.com (8.14.4/8.13.8) with ESMTP id xACCJHpi018994; Tue, 12 Nov 2019 12:19:17 GMT Received: from [10.191.24.133] (/10.191.24.133) by default (Oracle Beehive Gateway v4.0) with ESMTP ; Tue, 12 Nov 2019 04:19:17 -0800 Subject: Re: [PATCH RESEND v2 2/4] KVM: ensure grow start value is nonzero To: Sean Christopherson Cc: linux-kernel@vger.kernel.org, pbonzini@redhat.com, rkrcmar@redhat.com, rafael.j.wysocki@intel.com, joao.m.martins@oracle.com, mtosatti@redhat.com, kvm@vger.kernel.org, linux-pm@vger.kernel.org References: <1573041302-4904-1-git-send-email-zhenzhong.duan@oracle.com> <1573041302-4904-3-git-send-email-zhenzhong.duan@oracle.com> <20191111201320.GA7431@linux.intel.com> From: Zhenzhong Duan Organization: Oracle Corporation Message-ID: <0c8543e6-7664-cce9-c890-a10663d76d55@oracle.com> Date: Tue, 12 Nov 2019 20:19:14 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:60.0) Gecko/20100101 Thunderbird/60.9.1 MIME-Version: 1.0 In-Reply-To: <20191111201320.GA7431@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=9438 signatures=668685 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 suspectscore=0 malwarescore=0 phishscore=0 bulkscore=0 spamscore=0 mlxscore=0 mlxlogscore=781 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1910280000 definitions=main-1911120110 X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9438 signatures=668685 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=847 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1910280000 definitions=main-1911120110 Sender: linux-pm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-pm@vger.kernel.org On 2019/11/12 4:13, Sean Christopherson wrote: > On Wed, Nov 06, 2019 at 07:55:00PM +0800, Zhenzhong Duan wrote: >> vcpu->halt_poll_ns could be zeroed in certain cases (e.g. by >> halt_poll_ns = 0). If halt_poll_grow_start is zero, >> vcpu->halt_poll_ns will never be bigger than zero. >> >> Use param callback to avoid writing zero to halt_poll_grow_start. > This doesn't explain why allowing an admin to disable halt polling by > writing halt_poll_grow_start=0 is a bad thing. Paolo had the same > question in v1, here[1] and in the guest driver[2]. > > [1]https://lkml.kernel.org/r/57679389-6e4a-b7ad-559f-3128a608c28a@redhat.com > [2]https://lkml.kernel.org/r/391dd11b-ebbb-28ff-5e57-4a795cd16a1b@redhat.com Ok, answer all the same questions about grow_start=0 here. VCPU halt polling time may be nonzero even if grow_start=0, such as in below situation: 0=grow_start< block_ns< (vcpu->halt_poll_ns)< halt_poll_ns grow_start=0 has your mentioned effect only in below sequence: 1. set halt_poll_ns=0 to disable halt polling(this lead to vcpu->halt_poll_ns=0) 2. set grow_start=0 3. set halt_poll_ns to nonzero 4. Admin expect halt polling time auto adjust in range [0, nonzero], but polling time stick at 0. So I think we should use halt_poll_ns=0 to disable halt polling instead of grow_start=0. Zhenzhong